Magnetic-field-induced ferroelectric state in DyFeO3

Deterministic control of nanomagnetic spiral trajectories using an electric field

The intertwined nature of magnetic and electric degrees of freedom in magnetoelectric (ME) materials is well described by ME-coupling theory. When an external electric field is applied to a ME material, the ME coupling induces unique and intriguing magnetic responses. Such responses underpin the utilisation of ME materials across diverse applications, ranging from electromagnetic sensing to low-energy digital memory technologies. Here, we use small angle neutron scattering and discover a novel magnetic response within an archetypal chiral ME material, Cu2OSeO3. We find that the propagation direction of an incommensurate magnetic spiral is deterministically actuated and deflected along controllable trajectories. Furthermore, we predict the emergence of distinct non-linear regimes of spiral-deflection behaviour with external electric and magnetic fields, unlocking innovative devices that leverage controlled and customisable variations in macroscopic polarisation and magnetisation.

Implications of magnetic dilution of PrFeO3 with Bi3+ on its dielectric and magnetic properties

Research on functional oxide ceramics has tremendous translational potential for technological applications. Despite sharing a similar formula, BiFeO3 and REFeO3 (RE = rare earth) perovskites differ widely in structure and properties. The potential of substituting non-magnetic Bi3+ with a stereochemically active 6s2 lone pair in rare-earth ferrites remains largely unexplored. In this work, the consequences of replacing Pr3+ with Bi3+ on the dielectric and magnetic properties of PrFeO3 were investigated by synthesizing the samples using a solution combustion method. The inclusion of bismuth led to local site disorder and promoted the reduction of more amounts of Fe3+ to Fe2+, as verified by Raman and XPS measurements. The higher concentration of Fe2+ resulted in the formation of oxygen vacancies. The band gaps of the pure and Bi-substituted PrFeO3 samples were in the range of 1.90-2.08 eV. The field and temperature-dependent magnetic measurements of Pr1-xBixFeO3 confirmed the magnetic dilution. ZFC and FC measurements at low fields revealed a spin reorientation transition at 101 K in the case of Pr0.70Bi0.30FeO3, which supported the negative exchange bias effect at room temperature. The dielectric constant increased with an increase in bismuth content. Electronic structure calculations with charge density plots revealed the induction of polarization by the electric field in the Bi3+-containing samples. This was also verified through PUND measurements, which showed the existence of intrinsic and switchable polarization (0.17 μC cm-2). The random distribution of the stereochemically active 6s2 lone pair on Bi3+ has been proposed as the reason for the observed polarization.

Optical Excitation of Coherent THz Dynamics of the Rare-Earth Lattice through Resonant Pumping of f-f Electronic Transition in a Complex Perovskite DyFeO_{3}

Resonant pumping of the electronic f-f transitions in the orbital multiplet of dysprosium ions (Dy^{3+}) in a complex perovskite DyFeO_{3} is shown to impulsively launch THz lattice dynamics corresponding to the B_{2g} phonon mode, which is dominanted by the motion of Dy^{3+} ions. The findings, supported by symmetry analysis and density-functional theory calculations, not only provide a novel route for highly selective excitation of the rare-earth crystal lattices but also establish important relationships between the symmetry of the electronic and lattice excitations in complex oxides.

Role of Dy 4felectrons on magnetic coupling and reorientation in DyFeO3

Spin reorientation transition is an ubiquitous phenomenon observed in magnetic rare earth orthferrites RFeO3, which has garnered significant attention in recent years due to its potential applications in spintronics or magnetoelectric devices. Although a plenty of experimental works suggest that the magnetic interaction between R3+and Fe3+spins is at the heart of the spin reorientation, but a direct and conclusive theoretical support has been lacking thus far, primarily due to the challenging nature of handling R 4felectrons. In this paper, we explored DyFeO3as an example by means of comprehensive first principles calculations, and compared two different approaches, where the Dy 4felectrons were treated separately as core or valence states, aiming to elucidate the role of Dy 4felectrons, particularly in the context of the spin reorientation transition. The comparison provides a solid piece of evidence for the experimental argument that the Dy3+-Fe3+magnetic interactions play a vital role in triggering spin reorientation of Fe3+moments at low temperatures. The findings revealed here not only extend our understanding on the underlying mechanism for spin reorientation transition in RFeO3, but also highlight the importance of explicit description of R 4felectrons in rationally reproducing their structural, electronic and magnetic properties.

Ab Initio Investigation of the Structural, Elastic, Dynamic, Electronic, and Magnetic Properties of Cubic Perovskite CeCrO3

We presented the results of various aspects related to structural, elastic, electronic, dynamic, and magnetic parameters of cubic perovskite CeCrO3 by means of the full-potential linearized augmented plane wave (FP-LAPW) approach. The calculation of the unit cell volume against the total energy curve confirms that CeCrO3 exhibits higher energetic stability in the ferromagnetic (FM) order. Calculated structural aspects at equilibrium demonstrate excellent similarity to present information, lending credibility to our results. Moreover, monocrystalline elastic constants have been analyzed numerically. These constants provide insights into several related properties, including elastic anisotropy, mechanical stability, and several polycrystalline elastic aspects. Furthermore, the phonon dispersion curves obtained from our calculations reveal the existence of soft modes, which suggests the potential metastability of CeCrO3. Through an analysis of the energy band dispersions, the half-metallic nature of this material is confirmed, such as Eg = 3.00 and 3.13 eV for the HM state within generalized gradient approximations Perdew-Burke-Ernzerhof (GGA-PBE) and Tran-Blaha modified Becke-Johnson (TB-mBJ) calculations, respectively, as well as the FM total magnetic moment of 4.000 μB. Partial density of states (PDOS) aided in identifying the electronic states that contribute to the energy bands. Finally, the computed total magnetic moment aligns fit the theoretical findings available in the literature.

Transient Magnetoelectric Coupling Induced by the Dynamic Intertwinement between Exchange Striction and Compensation in GdFeO3

In this study, we investigate the dynamic magnetoelectric (ME) coupling behaviors of GdFeO3 under pulsed magnetic fields. When a magnetic field is applied along the c-axis, and the temperature is near the compensation temperature (Tcomp = 3.5 K), we observe a subtle transition involving the reversal of Fe3+ moments at approximately 0.8 T in magnetization (M) measurements. This transition induces a corresponding jump in electrical polarization (P), which is not present in the static field measurements. The dynamic intertwining between M and P signifies a competition between antiferromagnetic (AFM) coupling between Gd3+ and Fe3+ moments and their Zeeman energies. The robust AFM coupling leads to the reversal of Fe3+ moments near Tcomp, triggering the abrupt change in P. Based on the exchange striction mechanism in the ferrimagnetic GdFeO3, we propose the possibility of achieving highly magnetic field sensitive ME coupling near the compensation temperature in ferrimagnetic multiferroic orthoferrites.

Metal-Organic Precursor Synthesis, Structural Characterization, and Multiferroic Properties of GdFeO3 Nanoparticles

GdFeO₃ nanoparticles were fabricated by a facile metal-organic precursor method using citric acid as a complexing agent. The phase purity and structural analysis by powder X-ray diffraction and FTIR studies indicates that the material is highly crystalline with an orthorhombic structure. Electron microscopic (TEM and SEM) studies of rare earth ferrites reveal worm-shaped nanoparticles with an average grain size of 95 nm. The high-resolution TEM study provides an insightful image, which shows an interplanar spacing of approximately 0.12 nm that corresponds to the (112) crystalline plane. A high surface area of 231.5 m² g^-1 has been achieved with a mesoporous texture, which in turn gives a high dielectric constant. Well-defined hysteresis is obtained with a saturation magnetization of 17.5 emu g^-1, remanent magnetization of 3.9 emu g^-1, and coercive field of -446 Oe. Room-temperature ferroelectricity in GdFeO₃ nanoparticles has been found for the first time with no leaky current and hence may be used in multistate memory devices.

High-Magnetic-Sensitivity Magnetoelectric Coupling Origins in a Combination of Anisotropy and Exchange Striction

Magnetoelectric (ME) coupling is highly desirable for sensors and memory devices. Herein, the polarization (P) and magnetization (M) of the DyFeO₃ single crystal were measured in pulsed magnetic fields, in which the ME behavior is modulated by multi-magnetic order parameters and has high magnetic-field sensitivity. Below the ordering temperature of the Dy³⁺-sublattice, when the magnetic field is along the c-axis, the P (corresponding to a large critical field of 3 T) is generated due to the exchange striction mechanism. Interestingly, when the magnetic field is in the ab-plane, ME coupling with smaller critical fields of 0.8 T (a-axis) and 0.5 T (b-axis) is triggered. We assume that the high magnetic-field sensitivity results from the combination of the magnetic anisotropy of the Dy³⁺ spin and the exchange striction between the Fe³⁺ and Dy³⁺ spins. This work may help to search for single-phase multiferroic materials with high magnetic-field sensitivity.

Magnetostructural coupling in RFeO3 (R = Nd, Tb, Eu and Gd)

We investigate the interplay of magnetization and lattice vibrations in rare-earth orthoferrites RFeO₃, with a specific focus on non-symmetry-breaking anomalies. To do so, we study the magnetization, magnon excitations and lattice dynamics as a function of temperature in NdFeO₃, TbFeO₃, EuFeO₃ and GdFeO₃. The magnetization shows distinct temperature anomalous behavior for all investigated rare-earth orthoferrites, even in the compounds with no phase transitions occurring at those temperatures. Through spin-phonon coupling, these magnetic changes are mirrored by the FeO₆ rotation mode for all the studied RFeO₃, revealing a common magnetostructural effect associated with the octahedra rotations. The R³⁺ oscillation modes evidence a Fe³⁺/R³⁺ spins cross-talk for the NdFeO₃ and TbFeO₃ cases. Our work sheds light into the common magnetostructural coupling in rare-earth orthoferrites, and the important role of magnetic anisotropy and spin-orbit coupling strength of the R-Fe interactions on the spin-reorientation transition at high temperatures.

The magnetic structure of DyFeO3revisited: Fe spin reorientation and Dy incommensurate magnetic order

High resolution and high intensity neutron powder diffraction is used to study the ground state magnetic order and the spin reorientation transition in the orthoferrite DyFeO₃. The transition from the high temperaturek= 0 Γ₄(G_xA_yF_z) to the low temperature Γ₁(A_xG_yC_z) type order of the Fe-sublattice is found atT_SR= 73 K and does not show any thermal hysteresis. BelowT_N2= 4 K the Dy-sublattice orders in an incommensurate magnetic structure withk= [0, 0, 0.028] while the Fe-sublattice keeps its commensurate Γ₁type order. DyFeO₃is the first orthoferriteRFeO₃to possess an incommensurate magnetic order of the rare earth sublattice under zero field conditions; an important piece of information neglected in the recent discussion of its multiferroic properties.

Role of oxygen vacancies in colossal polarization in SmFeO3-δ thin films

The orthorhombic rare-earth manganates and ferrites multiferroics are promising candidates for the next generation multistate spintronic devices. However, their ferroelectric polarization is small, and transition temperature is far below room temperature (RT). The improvement of ferroelectricity remains challenging. Here, through the subtle strain and defect engineering, an RT colossal polarization of 4.14 μC/cm2 is achieved in SmFeO3-δ films, which is two orders of magnitude larger than its bulk and is also the largest one among the orthorhombic rare-earth manganite and ferrite family. Meanwhile, its RT magnetism is uniformly distributed in the film. Combining the integrated differential phase-contrast imaging and density functional theory calculations, we reveal the origin of this superior ferroelectricity in which the purposely introduced oxygen vacancies in the Fe-O layer distorts the FeO6 octahedral cage and drives the Fe ion away from its high-symmetry position. The present approach can be applied to improve ferroelectric properties for multiferroics.

Chemical design of a new displacive-type ferroelectric

Since the discovery of the ferroelectric perovskite-type oxide BaTiO₃ in 1943, numerous materials have been surveyed as candidates for new ferroelectrics. Perovskite-type materials have played a leading role in basic research and applications of ferroelectric materials since the last century. Experimentalists and theoreticians have developed a new materials design stream for post-perovskite materials. In this stream, we have mainly focused on the role of covalency in the evolution of ferroelectricity for displacive-type ferroelectrics in oxides. This perspective surveys the following topics: (1) crossover from quantum paraelectric to ferroelectric through a ferroelectric quantum critical point, (2) the role of cation-oxygen covalency in ferroelectricity and the crossover to quantum paraelectric in perovskite-type compounds, (3) off-center-induced ferroelectricity in perovskites, (4) second-order Jahn-Teller effect enhancement of ferroelectricity in lithium-niobate-type oxides, (5) the presence of four ferroelectric phases and structural transitions of phases of AFeO₃ with decreasing radius of A (A = La-Al), (6) tetrahedral ferroelectrics of perovskite-related Bi₂SiO₅ and wurtzites, (7) a rare type of polarization switching system in which the coordination number of ions in κ-Al₂O₃ systems changes between 4 and 6, and (8) lone-pair-electron-induced ferroelectrics in langasite-type compounds.

Low field control of spin switching and continuous magnetic transition in an ErFeO3 single crystal

The magnetic behavior of a rare-earth orthoferrite ErFeO₃ single crystal can be controlled by low magnetic fields from a few to hundreds of Oe. Here we investigated a high-quality ErFeO₃ single crystal in the temperature range of 5-120 K, with two types of spin switching in the field-cooled-cooling (FCC) and field-cooled-warming (FCW) processes below the temperature of the spin reorientation (SR) transition from Γ₄ to Γ₂ at 98-88 K. The magnitude of the applied magnetic fields can regulate two types of spin switching along the a-axis of the ErFeO₃ single crystal but does not affect the type and temperature range of the SR transition. An interesting "multi-step" type-II spin switching is observed in FCW under low magnetic fields (H < 18 Oe) just below the SR transition temperature, which is associated with the interaction and the change of magnetic configurations from rare-earth and iron magnetic sublattices. When the magnetic field is lower than 15 Oe, the type-II spin switching in the FCW process gradually changes to a continuous magnetic transition along the a-axis of the ErFeO₃ single crystal. As the magnetic field is reduced to less than 17 Oe, the type-I spin switching in the FCW process also transforms into a continuous magnetic transition. Understanding the magnetic reversal effects will help us explore the potential applications of these magnetic materials for future information devices.

Perovskite-structure TlBO3 (B = Cr, Mn) for thermomechanical and optoelectronic applications: an investigation via a DFT scheme

Here, we have employed the density functional theory on TlBO3 (B = Cr, Mn) to study the structural, mechanical, electronic, optical, and thermal properties for the first time. Spin polarization causes a metallic-to-semiconducting transition.

Low-energy spin dynamics in rare-earth perovskite oxides

We review recent studies of spin dynamics in rare-earth orthorhombic perovskite oxides of the type RMO₃, where R is a rare-earth ion and M is a transition-metal ion, using single-crystal inelastic neutron scattering (INS). After a short introduction to the magnetic INS technique in general, the results of INS experiments on both transition-metal and rare-earth subsystems for four selected compounds (YbFeO₃, TmFeO₃, YFeO₃, YbAlO₃) are presented. We show that the spectrum of magnetic excitations consists of two types of collective modes that are well separated in energy: gapped magnons with a typical bandwidth of <70 meV, associated with the antiferromagnetically (AFM) ordered transition-metal subsystem, and AFM fluctuations of <5 meV within the rare-earth subsystem, with no hybridization of those modes. We discuss the high-energy conventional magnon excitations of the 3dsubsystem only briefly, and focus in more detail on the spectacular dynamics of the rare-earth sublattice in these materials. We observe that the nature of the ground state and the low-energy excitation strongly depends on the identity of the rare-earth ion. In the case of non-Kramers ions, the low-symmetry crystal field completely eliminates the degeneracy of the multiplet state, creating a rich magnetic field-temperature phase diagram. In the case of Kramers ions, the resulting ground state is at least a doublet, which can be viewed as an effective quantum spin-1/2. Equally important is the fact that in Yb-based materials the nearest-neighbor exchange interaction dominates in one direction, despite the three-dimensional nature of the orthoperovskite crystal structure. The observation of a fractional spinon continuum and quantum criticality in YbAlO₃demonstrates that Kramers rare-earth based magnets can provide realizations of various aspects of quantum low-dimensional physics.

Multiferroic order parameters in rhombic antiferromagnetsRCrO3

Currently, active research is aimed at perovskite-based oxides, including rare earth orthochromites, which exhibit magnetoelectric properties owed to intrinsic magnetic interactions in external electric and magnetic fields. Due to a variety of structural instabilities and couplings in these materials, understanding the underlying magnetoelectric mechanisms is a challenge. In this paper, we explore magnetoelectric properties of the rare earth orthochromites in the framework of symmetry analysis. Our calculations show the presence inRCrO₃of electric dipole moments localized in the vicinity of Cr³⁺ions. The electric dipole moments, appearing due to the displacements of oxygen ions from their highly symmetric positions in the parent perovskite phase, are arranged in an antiferroelectric mode. We have demonstrated the presence of electric dipole moments in the unit cell ofRCrO_3,localized in the vicinity of Cr³⁺ions. The inversion symmetry breaks due to the displacements of oxygen ions from their highly symmetric positions in the parent perovskite phase, the electric dipoles become arranged in an antiferroelectric mode. We have introduced the basic distortive order parameters in consistence with the symmetry ofRCrO₃: the polar order parameters (D,Q₂,Q₃,P) and the axial order parameterΩ_band classified them according to the irreducible representations of theRCrO₃symmetry group (D_2h¹⁶). We have determined the symmetry-allowed couplings between distortive, ferroelectric and magnetic orderings and found possible exchange-coupled magnetic and ferroelectric structures. The presented analysis makes it possible to explain experimentally observed polarization reversal and the concomitant reorientation of spins in a series ofRCrO₃compounds and to predict the possible scenarios of phase transitions inRCrO₃.

An antisite defect mechanism for room temperature ferroelectricity in orthoferrites

Single-phase multiferroic materials that allow the coexistence of ferroelectric and magnetic ordering above room temperature are highly desirable, motivating an ongoing search for mechanisms for unconventional ferroelectricity in magnetic oxides. Here, we report an antisite defect mechanism for room temperature ferroelectricity in epitaxial thin films of yttrium orthoferrite, YFeO₃, a perovskite-structured canted antiferromagnet. A combination of piezoresponse force microscopy, atomically resolved elemental mapping with aberration corrected scanning transmission electron microscopy and density functional theory calculations reveals that the presence of Y_Fe antisite defects facilitates a non-centrosymmetric distortion promoting ferroelectricity. This mechanism is predicted to work analogously for other rare earth orthoferrites, with a dependence of the polarization on the radius of the rare earth cation. Our work uncovers the distinctive role of antisite defects in providing a mechanism for ferroelectricity in a range of magnetic orthoferrites and further augments the functionality of this family of complex oxides for multiferroic applications.

Oxygen vacancy mediated room-temperature ferromagnetism and band gap narrowing in DyFe0.5Cr0.5O3 nanoparticles

We report on the magnetic and optical properties of DyFe0.5Cr0.5O3 nanoparticles synthesized by a sol-gel method. Rietveld refinement of a powder X-ray diffraction (XRD) pattern confirms the formation of an orthorhombic disordered phase with the Pnma space group. The formation of nano-sized particles, with an average size of 42(±12) nm, was approximated by the transmission electron microscopy (TEM) image analysis. X-ray photoelectron spectroscopy (XPS) of this compound reveals the presence of Fe2+/Fe3+ and Cr2+/Cr3+ mixed-valence states as a consequence of oxygen vacancies present at the surface of nanoparticles. The temperature-dependent magnetization (M-T) shows a finite non-zero magnetization up to 300 K and the field-dependent magnetization (M-H) curve exhibits a weak ferromagnetic (WFM) nature at 300 K with a clear hysteresis loop, which is quite appealing compared to that of the previously reported micron-sized DyFe0.5Cr0.5O3. These observations indicate that the large concentration of uncompensated surface spin of nanoparticles could be responsible for the observed room-temperature ferromagnetism. Moreover, DyFe0.5Cr0.5O3 nanoparticles show a significantly narrow band gap (Eg ∼ 2.0 eV). Meanwhile, the oxygen vacancies may generate shallow trap energy levels within the band gap as observed from photoluminescence (PL) spectroscopy. The observed band gap narrowing by Fe doping and the effect of oxygen vacancies on the band gap are consistent with the predictions of density functional theory (DFT) calculations. The evidence of room-temperature ferromagnetism in DyFe0.5Cr0.5O3 nanoparticles compared to their bulk counterparts and the significantly narrow band gap in the visible range manifest the potential of this material in spintronic and optical applications.

Doping tuned spin reorientation and spin switching in praseodymium-samarium orthoferrite single crystals

We investigate the detailed analysis of the magnetic properties in a series of Pr_1-xSm_xFeO₃single crystals fromx= 0 to 1 with an interval of 0.1. Doping controlled spin reorientation transition temperatureT_SRΓ₄(G_x,A_y,F_z) to Γ₂(F_x,C_y,G_z) covers a wide temperature range including room temperature. A 'butterfly'-shape type-I spin switching with 180° magnetization reversal occurs below and above the magnetization compensation points inx= 0.4 to 0.8 compounds. Interestingly, in Pr_0.6Sm_0.4FeO₃single crystal, we find an inadequate spin reorientation transition accompanied by uncompleted type-I spin switching in the temperature region from 138 to 174 K. Furthermore, a type-II spin switching appears at 23 K, as evidenced from the magnetization curve in field-cooled-cooling (FCC) mode initially bifurcate from zero-field-cooled (ZFC) magnetization curve at 40 K and finally drops back to coincide the ZFC magnetization value at 23 K. Our current research reveals a strong and complex competition between Pr³⁺-Fe³⁺and Sm³⁺-Fe³⁺exchange interactions and more importantly renders a window to design spintronic device materials for future potential applications.

Nanoscale Magnetization Reversal by Magnetoelectric Coupling Effect in Ga0.6Fe1.4O3 Multiferroic Thin Films

The control of magnetism by electric means in single-phase multiferroic materials is highly desirable for the realization of next-generation magnetoelectric (ME) multifunctional devices. Nevertheless, most of these materials reveal either low working temperature or antiferromagnetic nature, which severely limits the practical applications. Herein, we selected room-temperature multiferroic Ga_0.6Fe_1.4O₃ (GFO) with ferrimagnetism to study electric-field-induced nanoscale magnetic domain reversal. The GFO thin film fabricated on the (111)-orientated Nb-doped SrTiO₃ single-crystal substrate was obtained through the pulsed laser deposition method. The test results indicate that the thin film not only exhibits ferroelectricity but also ferrimagnetism at room temperature. More importantly, reversible and nonvolatile nanoscale magnetic domains reversal under pure electrical fields is further demonstrated by taking advantage of its ME coupling effect with dependent origins based on iron ions. When providing an appropriate applied voltage, clear magnetic domain structures with large size can be easily manipulated. Meanwhile, the change ratio of the electrically induced magnetizations in the defined areas can reach up to 72%. These considerable merits of the GFO thin film may provide a huge potential in the ME multifunctional devices, such as the multi-value, low-energy-consuming, and nonvolatile memory and beyond.

Observation of novel charge ordering and spin reorientation in perovskite oxide PbFeO3

PbMO₃ (M = 3d transition metals) family shows systematic variations in charge distribution and intriguing physical properties due to its delicate energy balance between Pb 6s and transition metal 3d orbitals. However, the detailed structure and physical properties of PbFeO₃ remain unclear. Herein, we reveal that PbFeO₃ crystallizes into an unusual 2a_p × 6a_p × 2a_p orthorhombic perovskite super unit cell with space group Cmcm. The distinctive crystal construction and valence distribution of Pb²⁺_0.5Pb⁴⁺_0.5FeO₃ lead to a long range charge ordering of the -A-B-B- type of the layers with two different oxidation states of Pb (Pb²⁺ and Pb⁴⁺) in them. A weak ferromagnetic transition with canted antiferromagnetic spins along the a-axis is found to occur at 600 K. In addition, decreasing the temperature causes a spin reorientation transition towards a collinear antiferromagnetic structure with spin moments along the b-axis near 418 K. Our theoretical investigations reveal that the peculiar charge ordering of Pb generates two Fe³⁺ magnetic sublattices with competing anisotropic energies, giving rise to the spin reorientation at such a high critical temperature.

Non-collinear magnetism & multiferroicity: the perovskite case

The most important types of non-collinear magnetic orders that are realized in simple perovskite oxides are outlined in relation to multiferroicity. These orders are classified and rationalized in terms of a mimimal spin Hamiltonian, based on which the notion of spin-driven ferroelectricity is illustrated. These concepts find direct application in reference materials such as BiFeO3, GdFeO3 and TbMnO3 whose multiferroic properties are briefly reviewed.

Spin reorientation in antiferromagnetic Dy2FeCoO6 double perovskite

We explored the electronic and magnetic properties of the lanthanide double perovskite Dy₂FeCoO₆ by combining magnetization, Raman and Mössbauer spectroscopy and neutron diffraction along with density functional theory (DFT) calculations. Our magnetization measurements revealed two magnetic phase transitions in Dy₂FeCoO₆. First, a paramagnetic to antiferromagnetic transition at T _N = 248 K and subsequently, a spin reorientation transition at T _SR = 86 K. In addition, a field-induced magnetic phase transition with a critical field of H _c ≈ 20 kOe is seen at 2 K. Neutron diffraction data suggested cation-disordered orthorhombic structure for Dy₂FeCoO₆ in Pnma space group which is supported by Raman scattering results. The magnetic structures ascertained through representational analysis indicate that at T _N, a paramagnetic state is transformed to Γ₅(Cx, Fy, Az) antiferromagnetic structure while, at T _SR, Fe/Co moments undergo a spin reorientation to Γ₃(Gx, Ay, Fz). The refined magnetic moment of (Fe/Co) is 1.47(4) μ _B at 7 K. The antiferromagnetic structure found experimentally is supported through the DFT calculations which predict an insulating electronic state in Dy₂FeCoO₆.

Voltage Control of Magnetism above Room Temperature in Epitaxial SrCo1-xFexO3-δ

Searching for new materials and phenomena to enable voltage control of magnetism and magnetic properties holds compelling interest for the development of low-power nonvolatile memory devices. In particular, reversible and nonvolatile ON/OFF controls of magnetism above room temperature are highly desirable yet still elusive. Here, we report on a nonvolatile voltage control of magnetism in epitaxial SrCo_1-xFe_xO_3-δ (SCFO). The substitution of Co with Fe significantly changes the magnetic properties of SCFO. In particular, for the Co/Fe ratio of ∼1:1, a switch between nonmagnetic (OFF) and ferromagnetic (ON) states with a Curie temperature above room temperature is accomplished by ionic liquid gating at ambient conditions with voltages as low as ±2 V, even for films with thickness up to 150 nm. Tuning the oxygen stoichiometry via the polarity and duration of gating enables reversible and continuous control of the magnetization between 0 and 100 emu/cm³ (0.61 μ_B/f.u.) at room temperature. In addition, SCFO was successfully incorporated into self-assembled two-phase vertically aligned nanocomposites, in which the reversible voltage control of magnetism above room temperature is also attained. The notable structural response of SCFO to ionic liquid gating allows large strain couplings between the two oxides in these nanocomposites, with potential for voltage-controlled and strain-mediated functionality based on couplings between structure, composition, and physical properties.

Anisotropic and nonlinear magnetodielectric effects in orthoferrite ErFeO3 single crystals

In rare-earth orthoferrites, strongly correlated order parameters have been thoroughly investigated, which aims to find multiple functionalities such as multiferroic or magnetoelectric properties. We have discovered highly anisotropic and nonlinear magnetodielectric effects from detailed measurements of magnetoelectric properties in single-crystalline orthoferrite, ErFeO₃. Isothermal dielectric constant varies in shapes and signs depending on the relative orientations between the external electric and magnetic fields, which may be ascribed to the spin-phonon couplings. In addition, a dielectric constant with both electric and magnetic fields along the c axis exhibits two symmetric sharp anomalies, which are closely relevant to the spin-flop transition, below the ordering temperature of Er³⁺ spins, T_Er = 3.4 K. We speculate that the magnetostriction from the exchange couplings between Er³⁺ and Fe³⁺ magnetic moments would be responsible for this relationship between electric and magnetic properties. Our results present significant characteristics of the orthoferrite compounds and offer a crucial guide for exploring suitable materials for magnetoelectric functional applications.

Magnetic field tuning of spin resonance in TmFeO3 single crystal probed with THz transient

TmFeO₃, a canted antiferromagnet, has two intrinsic spin resonance modes in the terahertz (THz) frequency regime: quasi-ferromagnetic (q-FM) mode and quasi-antiferromagnetic (q-AFM) mode. Both the q-FM and q-AFM modes show strong magnetic field and temperature dependence. Hereby, by employing THz time-domain spectroscopy combined with external magnetic field and low temperature system, we systematically investigated the magnetic field induced frequency shift of q-FM and q-AFM modes as well as the temperature driven spin reorientation phase transition in TmFeO₃ single crystal. In contrast to the isotropic temperature dependent two-mode, the magnetic field dependence of two-mode is strongly anisotropic: the magnetic field applied along c-axis (a-axis) can harden (soften) the spin resonance frequency of q-FM mode for Γ₄ phase of TmFeO₃, and the field applied along b-axis shows negligible frequency shift for the q-FM mode, with the q-AFM mode relatively stable. The present study provides solid evidence that the magnetic anisotropy in rare earth orthoferrite plays a dominant role in the q-FM mode and the occurrence of spin reorientation phase transition. With the magnetic anisotropic energy obtained from the temperature dependent q-FM and q-AFM mode frequencies, we can predict both magnetic field and temperature dependence of spin resonance in TmFeO₃ single crystal via phenomenological analysis.

Spin structure and spin Hall magnetoresistance of epitaxial thin films of the insulating non-collinear antiferromagnet SmFeO3

We report a combined study of imaging the antiferromagnetic (AFM) spin structure and measuring the spin Hall magnetoresistance (SMR) in epitaxial thin films of the insulating non-collinear antiferromagnet SmFeO₃. X-ray magnetic linear dichroism photoemission electron microscopy measurements reveal that the AFM spins of the SmFeO₃(1 1 0) align in the plane of the film. Angularly dependent magnetoresistance measurements show that SmFeO₃/Ta bilayers exhibit a positive SMR, in contrast to the negative SMR expected in previously studied collinear AFMs. The SMR amplitude increases linearly with increasing external magnetic field at higher magnetic fields, suggesting that field-induced canting of the AFM spins plays an important role. In contrast, around the coercive field, no detectable SMR signal is observed, indicating that the SMR of the AFM and canting magnetization components cancel out. Below 50 K, the SMR amplitude increases sizably by a factor of two as compared to room temperature, which likely correlates with the long-range ordering of the Sm ions. Our results show that the SMR is a sensitive technique for non-equilibrium spin systems of non-collinear AFMs.

An evidence of local structural disorder across spin-reorientation transition in DyFeO3: an extended x-ray absorption fine structure (EXAFS) study

The present work is aimed at exploring the local atomic structure modifications related to the spin reorientation transition (SRT) in DyFeO₃ orthoferrite exploiting x-ray absorption fine structure (XAFS) spectroscopy. For this purpose we studied by XAFS the evolution of the local atomic structure around Fe and Dy as function of temperature (10-300 K) in a DyFeO₃ sample having the SRT around 50-100 K. For sake of comparison we studied a YFeO₃ sample having no SRT. The analysis of the extended region has revealed an anomalous trend of Fe-O nearest neighbour distribution in DFO revealing (i) a weak but significant compression with increasing temperature above the SRT and (ii) a peculiar behavior of mean square relative displacement (MSRD) [[Formula: see text]] of Fe-O bonds showing an additional static contribution in the low temperature region, below the SRT. These effects are absent in the YFO sample supporting these anomalies related to the SRT. Interestingly the analysis of Dy L ₃-edge data also reveal anomalies in the Dy-O neighbour distribution associated to the SRT, pointing out a role of magnetic Re ions across [Formula: see text]. These results point out micro-structural modification at both Fe and Dy sites associated to the magnetic transitions in DFO, it can be stated in general terms that such local distortions across [Formula: see text] and magnetic Re³⁺ may be present in other orthoferrites exhibiting multiferroic nature.

Multiferroic ABO3 Transition Metal Oxides: a Rare Interaction of Ferroelectricity and Magnetism

This review article summarizes the development of different kinds of materials that evolved interest in all field of science particularly on new nano-materials which possess both electric and magnetic properties at the nanoscale. Materials of such kind possessing both magnetic and electric properties have tremendous applications and own an intensive research activity. These materials induce new properties which are particularly important in electronic and magnetic devices and even in the materials where magnetic property will change by electric field or vice versa. The discovery of such ferroic properties for scientific applications is the need of hour and spreads an exciting new area that has technical and commercial potential for the discovery of advanced materials. In recent studies, the actual path by which the multiferroic properties exist has been focused and new metal oxide compounds were discovered. The understanding of the structure of these compounds through research describes a wide range of applications and the challenges of these multiferroic materials that need to be explored. In this study, fundamental aspects and structural variations of ternary transition metal oxides have been covered which possess novel properties in storage devices such as hard disk platters and magnetic read heads.

Electric-field control of ferromagnetism through oxygen ion gating

Electric-field-driven oxygen ion evolution in the metal/oxide heterostructures emerges as an effective approach to achieve the electric-field control of ferromagnetism. However, the involved redox reaction of the metal layer typically requires extended operation time and elevated temperature condition, which greatly hinders its practical applications. Here, we achieve reversible sub-millisecond and room-temperature electric-field control of ferromagnetism in the Co layer of a Co/SrCoO2.5 system accompanied by bipolar resistance switching. In contrast to the previously reported redox reaction scenario, the oxygen ion evolution occurs only within the SrCoO2.5 layer, which serves as an oxygen ion gating layer, leading to modulation of the interfacial oxygen stoichiometry and magnetic state. This work identifies a simple and effective pathway to realize the electric-field control of ferromagnetism at room temperature, and may lead to applications that take advantage of both the resistance switching and magnetoelectric coupling.

Single crystal polarized neutron diffraction study of the magnetic structure of HoFeO3

Polarised neutron diffraction measurements have been made on HoFeO₃ single crystals magnetised in both the [0 0 1] and [1 0 0] directions (Pbnm setting). The polarisation dependencies of Bragg reflection intensities were measured both with a high field of [Formula: see text] T parallel to [0 0 1] at [Formula: see text] K and with the lower field [Formula: see text] T parallel to [1 0 0] at [Formula: see text] K. A Fourier projection of magnetization induced parallel to [0 0 1], made using the hk0 reflections measured in 9 T, indicates that almost all of it is due to alignment of Ho moments. Further analysis of the asymmetries of general reflections in these data showed that although, at 70 K, 9 T applied parallel to [0 0 1] hardly perturbs the antiferromagnetic order of the Fe sublattices, it induces significant antiferromagnetic order of the Ho sublattices in the [Formula: see text] plane, with the antiferromagnetic components of moment having the same order of magnitude as the induced ferromagnetic ones. Strong intensity asymmetries measured in the low temperature [Formula: see text] structure with a lower field, 0.5 T [Formula: see text] [1 0 0] allowed the variation of the ordered components of the Ho and Fe moments to be followed. Their absolute orientations, in the [Formula: see text] domain stabilised by the field were determined relative to the distorted perovskite structure. This relationship fixes the sign of the Dzyalshinski-Moriya (D-M) interaction which leads to the weak ferromagnetism. Our results indicate that the combination of strong y-axis anisotropy of the Ho moments and Ho-Fe exchange interactions breaks the centrosymmetry of the structure and could lead to ferroelectric polarization.

Improper electric polarization in simple perovskite oxides with two magnetic sublattices

ABO₃ perovskite oxides with magnetic A and B cations offer a unique playground to explore interactions involving two spin sublattices and the emergent effects they may drive. Of particular interest is the possibility of having magnetically driven improper ferroelectricity, as in the much studied families of rare-earth orthoferrites and orthochromites; yet, the mechanisms behind such effects remain to be understood in detail. Here we show that the strongest polar order corresponds to collinear spin configurations and is driven by non-relativistic exchange-strictive mechanisms. Our first-principles simulations reveal the dominant magnetostructural couplings underlying the observed ferroelectricity, including a striking magnetically driven piezoelectric effect. Further, we derive phenomenological and atomistic theories that describe such couplings in a generic perovskite lattice. This allows us to predict how the observed effects can be enhanced, and even how similar ones can be obtained in other perovskite families.

Magnetically-driven ferroelectricity holds the key for novel multiferroic effects in perovskite oxides, but it remains poorly understood. Here, Zhao et al. determine the dominant magnetostructural couplings that yield improper ferroelectricity in a generic perovskite with two spin sublattices.

Electronic structure, magnetism and optical properties of orthorhombic GdFeO3 from first principles

The electronic structure, magnetism and optical properties of orthorhombic GdFeO₃ are investigated in terms of density-functional-theory calculations..

The crucial role of Mn spiral spin order in stabilizing the Dy–Mn exchange striction in multiferroic DyMnO3

Mn spiral spin ordering can be a prerequisite for the symmetric Dy–Mn exchange striction in DyMnO₃.

Tuning the Weak Ferromagnetic States in Dysprosium Orthoferrite

RFeO₃ orthoferrites, where R is a rare-earth ion of the lanthanide series, are attracting attention mostly because of their promising fast spin dynamics. The magnetic properties of these materials seem to crucially depend on whether the magnetizations of the R and Fe ions’ weak ferromagnetic (WFM) components are parallel or antiparallel to each other. Here, we report an extensive investigation of a high-quality DyFeO₃ single crystal in which the induced Dy³⁺ magnetization (F_Dy) has a natural tendency to be antiparallel to Fe³⁺ sublattice magnetization (F_Fe) within a large temperature window. Moreover, we find that specific variations of temperature and applied magnetic fields allow us to make F_Dy parallel to F_Fe, or force a spin-flip transition in F_Fe, among other effects. We found three different magnetic states that respond to temperature and magnetic fields, i.e. linear versus constant or, alternatively, presenting either behavior depending on the history of the sample. An original magnetic field-versus-temperature phase diagram is constructed to indicate the region of stability of the different magnetic phases, and to reveal the precise conditions yielding sudden spin switching and reversals. Knowledge of such a phase diagram is of potential importance to applications in spintronics and magnetic devices.

Observation of re-entrant spin reorientation in TbFe1-xMnxO3

We report a spin reorientation from Γ4(Gx, Ay, Fz) to Γ1(Ax, Gy, Cz) magnetic configuration near room temperature and a re-entrant transition from Γ1(Ax, Gy, Cz) to Γ4(Gx, Ay, Fz) at low temperature in TbFe1-xMnxO3 single crystals by performing both magnetization and neutron diffraction measurements. The Γ4 - Γ1 spin reorientation temperature can be enhanced to room temperature when x is around 0.5 ~ 0.6. These new transitions are distinct from the well-known Γ4 - Γ2 transition observed in TbFeO3, and the sinusoidal antiferromagnetism to complex spiral magnetism transition observed in multiferroic TbMnO3. We further study the evolution of magnetic entropy change (-ΔSM) versus Mn concentration to reveal the mechanism of the re-entrant spin reorientation behavior and the complex magnetic phase at low temperature. The variation of -ΔSM between a and c axes indicates the significant change of magnetocrystalline anisotropy energy in the TbFe1-xMnxO3 system. Furthermore, as Jahn-Teller inactive Fe(3+) ions coexist with Jahn-Teller active Mn(3+) ions, various anisotropy interactions, compete with each other, giving rise to a rich magnetic phase diagram. The large magnetocaloric effect reveals that the studied material could be a potential magnetic refrigerant. These findings expand our knowledge of spin reorientation phenomena and offer the alternative realization of spin-switching devices at room temperature in the rare-earth orthoferrites.

Symmetry conditions for type II multiferroicity in commensurate magnetic structures

Type II multiferroics are magnetically ordered phases that exhibit ferroelectricity as a magnetic induced effect. We show that in single-k magnetic phases the presence in the paramagnetic phase of non-symmorphic symmetry combined with some specific type of magnetic propagation vector can be sufficient for the occurrence of this type of multiferroic behaviour. Other symmetry scenarios especially favourable for spin driven multiferroicity are also presented. We review and classify known type II multiferroics under this viewpoint. In addition, some other magnetic phases which due to their symmetry properties can exhibit type II multiferroicity are pointed out.

Non-collinear magnetism in multiferroic perovskites

We present an overview of the current interest in non-collinear magnetism in multiferroic perovskite crystals. We first describe the different microscopic mechanisms giving rise to the non-collinearity of spins in this class of materials. We discuss, in particular, the interplay between non-collinear magnetism and ferroelectric and antiferrodistortive distortions of the perovskite structure, and how this can promote magnetoelectric responses. We then provide a literature survey on non-collinear multiferroic perovskites. We discuss numerous examples of spin cantings driving weak ferromagnetism in transition metal perovskites, and of spin-induced ferroelectricity as observed in the rare-earth based perovskites. These examples are chosen to best illustrate the fundamental role of non-collinear magnetism in the design of multiferroicity.

Continuous Magnetoelectric Control in Multiferroic DyMnO3 Films with Twin-like Domains

The magnetic control of ferroelectric polarization is currently a central topic in the multiferroic researches, owing to the related gigantic magnetoelectric coupling and fascinating physics. Although a bunch of novel magnetoelectric effect have been discovered in multiferroics of magnetic origin, the manipulation of polarization was found to be fundamentally determined by the microscopic origin in a certain multiferroic phase, hindering the development of unusual magnetoelectric control. Here, we report emergent magnetoelectric control in DyMnO₃/Nb:SrTiO₃ (001) films showing twin-like domain structure. Our results demonstrate interesting magnetically induced partial switch of polarization due to the coexistence of polarizations along both the a-axis and c-axis enabled by the twin-like domain structure in DyMnO₃ films, despite the polarization-switch was conventionally believed to be a one-step event in the bulk counterpart. Moreover, a continuous and periodic control of macroscopic polarization by an in-plane rotating magnetic field is evidenced in the thin films. This distinctive magnetic manipulation of polarization is the consequence of the cooperative action of the twin-like domains and the dual magnetic origin of polarization, which promises additional applications using the magnetic control of ferroelectricity.

Tailoring the magnetic and magnetoelectric properties of rare earth orthoferrites for room temperature applications

The M(T) curve shows negative magnetization value for samples containing Er ions. The dielectric constant value does not show any anomaly around the magnetic transition temperature. The temperature at which maximum MDE effect observed corresponds to dielectric loss maxima.

Interplay between 3d-3d and 3d-4f interactions at the origin of the magnetic ordering in the Ba₂LnFeO₅ oxides

A new family of oxides in which 3d-3d and 3d-4f interactions are of comparable strength has been synthesized and characterized both from structural and physical viewpoints. These compounds of formulation Ba2LnFeO5 (Ln  =  Sm, Eu, Gd, Dy, Ho, Er, Yb) are isotypic to the perovskite derivative Ba2YFeO5. They exhibit an original structure consisting of isolated FeO4 tetrahedra linked via LnO6 (or YO6) octahedra. Magnetic and calorimetric measurements show that all these compounds exhibit a unique, antiferromagnetic transition involving both the 3d and 4f ions. The antiferromagnetic properties of the Ln  =  Y phase (non-magnetic Y(3+)) and of the Ln  =  Eu (non-magnetic ground state multiplet of Eu(3+)) are ascribed to super-super exchange Fe-O-O-Fe interactions, leading to the lowest T(N) (5.5 K for Y and 4.6 K for Eu). The introduction of a magnetic lanthanide, i.e. Ln  =  Sm, Gd, Dy, Ho, Er, Yb, in the octahedral sites, leads to larger T(N) values (up to 9.8 K for Ln  =  Yb). It is found that several mechanisms must be taken into account to explain the complex evolution of the magnetic properties along the Ba2LnFeO5 series. In particular, the super-exchange Ln-O-Fe, as well as the on-site Ln(3+) magnetocrystalline anisotropy, are suggested to play crucial roles. This Ba2LnFeO5 series offers a rare opportunity to investigate experimentally a situation where the 3d-3d and 3d-4f interactions co-operate on an equal footing to trigger a unique long-range magnetic ordering in insulating oxides.

Piezomagnetoelectric Effect of Spin Origin in Dysprosium Orthoferrite

The piezomagnetoelectric effect, namely, the simultaneous induction of both the ferromagnetic moment and electric polarization by an application of uniaxial stress, was demonstrated in the nonferroelectric antiferromagnetic ground state of DyFeO(3). The induced electric polarization and ferromagnetic moment are coupled with each other, and monotonically increase with increasing uniaxial stress. The present work provides a new guiding principle for designing multiferroics where its magnetic symmetry is broken by external uniaxial stress.

Control of magnetism by electric fields

The electrical manipulation of magnetism and magnetic properties has been achieved across a number of different material systems. For example, applying an electric field to a ferromagnetic material through an insulator alters its charge-carrier population. In the case of thin films of ferromagnetic semiconductors, this change in carrier density in turn affects the magnetic exchange interaction and magnetic anisotropy; in ferromagnetic metals, it instead changes the Fermi level position at the interface that governs the magnetic anisotropy of the metal. In multiferroics, an applied electric field couples with the magnetization through electrical polarization. This Review summarizes the experimental progress made in the electrical manipulation of magnetization in such materials, discusses our current understanding of the mechanisms, and finally presents the future prospects of the field.