Temperature dependent structural properties of Mn1.90M0.10O3(M = Cr and Fe)

The polycrystalline samples of Mn1.90Cr0.10O3(MCO) and Mn1.90Fe0.10O3(MFO) have been investigated for their temperature dependent magnetic and structural properties. The Cr and Fe substitutions have significant effect on the magnetic and structural properties of Mn2O3. Like pristine Mn2O3, the Cr and Fe substituted samples MCO and MFO also exhibit two antiferromagnetic transitions; one at ∼77 K, ∼80 K, respectively and another at ∼40 K. Our room temperature synchrotron x-ray powder diffraction (SXRD) results confirm that both the MCO and MFO samples crystallize in cubic symmetry. The temperature dependent SXRD results demonstrate the cubic to orthorhombic structural transition for the studied samples. The pristine Mn2O3shows cubic to orthorhombic transition around 310 K, whereas this structural transition shifted towards lower temperature side with these substitutions i.e. around 240 K for MCO and 260 K for MFO. Interestingly, the centrosymmetricPcabto non-centrosymmetricPca21change in symmetry is also resolved at the ferroelectric ordering temperature for MCO.

Integrated experimental and theoretical studies on structural and magnetic properties of thin films of double perovskite ruthenates: Ba2DyRuO6 & Sr2DyRuO6

Thin films of double perovskite ruthenates, viz., Ba2DyRuO6 (BDRO) and Sr2DyRuO6 (SDRO), have been successfully grown on a SrTiO3 substrate using the pulsed laser deposition technique. The BDRO samples crystallizes in cubic structure, while SDRO exhibits monoclinic structure as revealed in their X-Ray diffraction examination. Temperature-dependent magnetization measurements suggest the presence of ferromagnetism in BDRO, while paramagnetism is present for the SDRO thin film. Surprisingly, both films show canted antiferromagnetism at ∼T = 5 K as revealed in their isothermal magnetization curves. The inverse susceptibility has been fitted to the Curie-Weiss law for the SDRO sample, where the Curie temperature (TC ∼ -336.6 K) has been obtained, thus suggesting the prevalence of antiferromagnetic interactions. The existence of the canted magnetism at a lower temperature may be attributed to the Dzyaloshinskii-Moriya (D-M) interactions in the monoclinic SDRO sample due to structural distortion. However, the emergence of canted antiferromagnetism at lower temperatures (5 K) in the BDRO sample with cubic symmetry having no D-M interactions may be attributed to the various modifications at the surface of the thin films. Overall, a comparison made between the magnetic properties of both the thin films i.e., BDRO & SDRO, reveals the suppression of bulk magnetic ordering when compared to their bulk counterparts. The possible reason for the absence of any magnetic ordering in these thin films may be due to any modifications in superexchange interactions, any exchange bias, stress-strain, or uncompensated spins present in these types of thin films. UV-visible measurements for both the samples reveal a direct influence of the A-site element (Sr/Ba) on their band gaps, i.e., 3.66 eV and 2.59 eV for BDRO and SDRO samples, respectively, hence suggesting their insulating nature. We have also carried out first principles calculations with DFT using the CASTEP software to gain more insights into the experimental data. These thin films with insulating-antiferromagnetic properties may be crucial for "spintronics devices".

Strain assisted magnetoelectric coupling in ordered nanomagnets of CoFe2O4/SrRuO3/(Pb(Mg1/3Nb2/3)O3-PbTiO3) heterostructures

We have explored the electric field controlled magnetization in the nanodot CoFe₂O₄/SrRuO₃/PMN-PT (CFO/SRO/PMN-PT) heterostructures. Ordered ferromagnetic CFO nanodots (∼300 nm lateral dimension) are developed on the PMN-PT substrate (ferroelectric as well as piezoelectric) using a nanostencil-mask pattering method during pulsed laser deposition. The nanostructures reveal electric field induced magnetization reversal in the single domain CFO nanodots through transfer of piezostrains from the piezoelectric PMN-PT substrate to the CFO. Further, electric field modulated spin structure of CFO nanomagnets is analyzed by using x-ray magnetic circular dichroism (XMCD). The XMCD analysis reveals cations (Fe³⁺/Co²⁺) redistribution on the octahedral and tetrahedral site in the electric field poled CFO nanodots, establishing the strain induced magneto-electric coupling effects. The CFO/SRO/PMN-PT nanodots structure demonstrate multilevel switching of ME coupling coefficient (α) by applying selective positive and negative electric fields in a non-volatile manner. The retention of two stable states ofαis illustrated for ∼10⁶seconds, which can be employed to store the digital data in non-volatile memory devices. Thus the voltage controlled magnetization in the nanodot structures leads a path towards the invention of energy efficient high-density memory devices.

Robust electronic and tunable magnetic states in Sm2 NiMnO6ferromagnetic insulator

Ferromagnetic insulators (FM-Is) are the materials of interest for the new generation quantum electronic applications. Here, we have investigated the physical observables depicting FM-I ground states in epitaxial Sm₂NiMnO₆(SNMO) double perovskite thin films fabricated under different conditions to realize the different level of Ni/Mn anti-site disorders (ASDs). The presence of ASDs immensely influence the characteristic magnetic and anisotropy behaviors in SNMO system by introducing short scale antiferromagnetic interactions in predominant long range FM ordered host matrix. Charge disproportion between cation sites, in the form of Ni²⁺+ Mn⁴⁺→ Ni³⁺+ Mn³⁺, causes mixed valency in both Ni and Mn species, which is found insensitive to ASD concentrations. Temperature dependent photo emission, photo absorption measurements duly combined with cluster model configuration interaction simulations, suggest that the eigenstates of Ni and Mn cations can be satisfactorily described as a linear combination of the unscreeneddⁿand screeneddn+1L̲(L̲: O 2phole) states. The electronic structure across the Fermi level (E_F) exhibits closely spaced Ni 3d, Mn 3dand O 2pstates. From occupied and unoccupied bands, estimated values of the Coulomb repulsion energy (U) and ligand to metal charge transfer energy (Δ), indicate charge transfer insulating nature, where remarkable modification in Ni/Mn 3d-O 2phybridization takes place across the FM transition temperature. Existence of ASD broadens the Ni, Mn 3dspectral features, whereas the spectral positions are found to be unaltered. Hereby, present work demonstrates SNMO thin film as a FM-I system, where the FM state can be tuned by manipulating ASD in the crystal structure, while the I state remains intact.

Evolution from sinusoidal to collinear A-type antiferromagnetic spin-ordered magnetic phase transition in Tb1-xPrxMnO3solid solution

The present study reports on the structural and magnetic phase transitions in Pr-doped polycrystalline Tb_0.6Pr_0.4MnO₃, using high-resolution neutron powder diffraction (NPD) collected at SINQ spallation source, to emphasize the suppression of the sinusoidal magnetic structure of pure TbMnO₃and the evolution to a collinear A-type antiferromagnetic ordering. The phase purity, Jahn-Teller distortion, and one-electron bandwidth for e_gorbital of Mn³⁺cation have been calculated for polycrystalline Tb_0.6Pr_0.4MnO_3,in comparison to the parent materials TbMnO₃and PrMnO₃, through the Rietveld refinement study from x-ray diffraction data at room temperature, which reveals the GdFeO₃type orthorhombic structure of Tb_0.6Pr_0.4MnO₃havingPnmaspace group symmetry. The temperature-dependent zero field-cooled and field-cooled dc magnetization study at low temperature down to 5 K reveals a variation in the magnetic phase transition due to the effect of Pr³⁺substitution at the Tb³⁺site, which gives the signature of the antiferromagnetic nature of the sample, with a weak ferromagnetic component at low temperature-induced by an external magnetic field. The field-dependent magnetization study at low temperatures gives the weak coercivity having the order of 2 kOe, which is expected due to the canted-spin arrangement or ferromagnetic nature of Terbium ordering. The NPD data for Tb_0.6Pr_0.4MnO₃confirms that the nuclear structure of the synthesized sample maintains its orthorhombic symmetry down to 1.5 K. Also, the magnetic structures have been solved at 50 K, 25 K, and 1.5 K through the NPD study, which shows an A-type antiferromagnetic spin arrangement having the magnetic space groupPn'ma'.

Mixed Mott-Hubbard and charge transfer nature of 4H-SrMnO3thin film on Si (100)

Room temperature electronic structure of polycrystalline 4H-SrMnO₃thin film grown on Si (100) substrate has been studied using resonance photo emission spectroscopy and soft x-ray absorption spectroscopy measurements. Presence of charge transfer screen Mn 3dⁿLfinal state along with the 3d^n-1final state at the valence band edge of 4H-SrMnO₃thin film confirms that the ground state is strongly mixed between Mn 3dand O 2pstates. The estimated equivalent values of on-site Coulomb interaction energy (U) and O 2pto Mn 3d- charge transfer energy (Δ) (U≈ Δ ≈ 4.8 eV) from the combination of occupied and unoccupied spectra further confirm the intermediate Mott-Hubbard and charge transfer insulator nature of 4H-SrMnO₃film. Despite having similar Mn 4+ valence state in 4H-SrMnO₃and cubic SrMnO₃, 4H phase is observed to reveal much higher band gap ∼1.5 eV than the cubic phase (0.3 eV), which arises due to different MnO₆octahedra environment.

Role of Ni substitution on structural, magnetic and electronic properties of epitaxial CoCr2O4 spinel thin films

Cubic spinel CoCr2O4 has recently attained attention due to its multiferroic properties. However, the Co site substitution effect on the structural and magnetic properties has rarely been studied in thin film form. In this work, the structural and magnetic properties of Co1-x Ni x Cr2O4 (x= 0, 0.5) epitaxial thin films deposited on MgAl2O4 (100) and MgO (100) substrates to manipulate the nature of strain in the films using pulsed laser deposition (PLD) technique are presented. The epitaxial nature of the films was manifested through x-ray diffraction (XRD), reciprocal space mapping (RSM) and Rutherford backscattering spectrometry (RBS) measurements. Raman measurements revealed a disappearance of characteristic A 1 g and F 2 g modes of the CoCr2O4 with increase in the Ni content. Atomic force microscopy (AFM) and field emission scanning electron microscopy (FE-SEM) studies show a modification of the surface morphology upon Ni substitution. Magnetic measurements disclose that the ferrimagnetic Curie temperature (T C) of the CoCr2O4 in thin film grown on MgAl2O4 (100) and MgO (100) substrates were found to be 100.6 ± 0.5 K and 93.8 ± 0.2 K, respectively. With Ni substitution the T C values were found to be enhanced to 104.5 ± 0.4 K for MgAl2O4 (100) and 108.5 ± 0.6 K for MgO (100) substrates. X-ray photoelectron spectroscopy (XPS) suggests Cr3+ oxidation states in the films, while Co ions are present in a mixed Co2+/Co3+ oxidation state. The substitution of Ni at Co site significantly modifies the line shape of the core level as well as the valence band. Ni ions are also found to be in a mixed 2+/3+ oxidation state. O 1s core level display asymmetry related to possible defects like oxygen vacancies in the films.

Structural, ferroelectric and dielectric properties of multiferroic YMnO3 synthesized via microwave assisted radiant hybrid sintering

In this work, multiferroic YMnO₃ ceramic samples prepared via microwave assisted radiant heating method (at 4 different microwave power percentage: 0, 15, 30 and 50) were studied to investigate their structural, ferroelectric and dielectric properties. In Raman measurement, the A₁ Raman scattering line at ∼ 683 cm^-1 is much stronger than other Raman modes and dominates the Raman spectra in all samples. The observed Raman modes identify the hexagonal YMnO₃ type structure of studied samples. YMnO₃ samples prepared at different microwave power displayed variation in ferroelectric polarization. The dielectric constant and dielectric loss tangent variation across different frequencies is also explored for these samples.

Elucidating the origin of magnetic ordering in ferroelectric BaTiO3- d thin film via electronic structure modification

With the motive of unraveling the origin of native vacancy induced magnetization in ferroelectric perovskite oxide systems, here we explore the consequences of electronic structure modification in magnetic ordering of oxygen deficient epitaxial BaTiO[Formula: see text] thin films. Our adapted methodology employs state-of-the-art experimental approaches viz. photo-emission, photo-absorption spectroscopies, magnetometric measurements duly combined with first principles based theoretical methods within the frame work of density functional theory (DFT and DFT+U) calculations. Oxygen vacancy (O[Formula: see text]) is observed leading partial population of Ti 3d (t _2g ), which induces defect state in electronic structure near the Fermi level and reduces the band gap. The oxygen deficient BaTiO_2.75 film reveals Mott-Hubbard insulator characteristic, in contrast to the band gap insulating nature of the stoichiometric BaTiO₃. The observed magnetic ordering is attributed to the asymmetric distribution of spin polarized charge density in the vicinity of O[Formula: see text] site, which originates unequal magnetic moment values at first and second nearest neighboring Ti sites, respectively. Hereby, we present an exclusive method for maneuvering the band gap and on-site electron correlation energy with consequences on magnetic properties of BaTiO[Formula: see text] system, which can open a gateway for designing novel single phase multiferroic system.

Magnetically retrievable Ce-doped Fe3O4 nanoparticles as scaffolds for the removal of azo dyes

Considering the significant impact of magnetically retrievable nanostructures, herein, Fe₃O₄ and Ce-doped Fe₃O₄ nanoparticles were employed as scaffolds for the removal of the Reactive Black 5 (RB5) azo dye. We synthesized the Ce-doped Fe₃O₄ nanoparticles via hydrothermal treatment at 120 °C for 10 h with varying cerium concentrations (1.5–3.5%) and characterized them using basic techniques such as FTIR and UV-visible spectroscopy, and XRD analysis. The retention of their magnetic behaviors even after cerium amalgamation was demonstrated and confirmed by the VSM results. FESEM and EDX were used for the morphological and purity analysis of the synthesized nanoabsorbents. XPS was carried out to determine the electronic configuration of the synthesized samples. The porosity of the magnetic nanoparticles was investigated by BET analysis, and subsequently, the most porous sample was further used in the adsorption studies for the cleanup of RB5 from wastewater. The dye adsorption studies were probed via UV-visible spectroscopy, which indicated the removal efficiency of 87%. The prepared Ce-doped Fe₃O₄ nanoabsorbent showed the high adsorption capacity of 84.58 mg g⁻¹ towards RB5 in 40 min. This is attributed to the electrostatic interactions between the nanoabsorbent and the dye molecules and high porosity of the prepared sample. The adsorption mechanism was also analyzed. The kinetic data well-fitted the pseudo-first-order model, and the adsorption capability at different equilibrium concentrations of the dye solution indicated monolayer formation and chemisorption phenomena. Furthermore, the magnetic absorbent could be rapidly separated from the wastewater using an external magnetic field after adsorption.

Considering the significant impact of magnetically retrievable nanostructures, herein, Ce-doped Fe₃O₄ nanoparticles were employed as scaffolds for the removal of the Reactive Black 5 (RB5), an azo dye.

Effect of impurities on the long-distance and Zhang-Rice dimers in the quantum magnet Sr14Cu24O41

We study the effect of impurities on the two types of spin-dimers in the hybrid chain-ladder spin 1/2 quantum magnet SrCuO. Four different impurities were used, namely, the non-magnetic Zn (0.0025 and 0.01 per Cu) and Al (0.0025 and 0.01 per Cu), and magnetic Ni (0.0025 and 0.01 per Cu) and Co (0.01, 0.03, 0.05 and 0.1 per Cu). These impurities were doped in high-quality single-crystals synthesized by the floating-zone method. The magnetic susceptibility of pristine SrCuOis analyzed rigorously to confirm that at low temperatures (K), the 'free' spins in the chains undergo a long-distance dimerization as proposed in a recent study (Sahlinget al2015Nat. Phys.11255). The effect of impurity on these dimers is analyzed by measuring the specific heat down toK. We found that even at the lower impurity concentration, the long-distance dimers are significantly severed but the quantum entangled spin dimerized state of the chains persists. On the other hand, the other type of spin dimers that form at relatively higher temperatures via an intervening Zhang-Rice singlet are found to be practically unaffected at the lower impurity concentration; but at 1% doping these dimers are considerably severed. The effect of Co impurity turned out to be most unusual displaying a strongly anisotropic response, and with a dimerization gap that suppresses faster along the chain/ladder direction than perpendicular to it as a function of increasing Co concentration.

Phase coexistence and the magnetic glass-like phase associated with the Morin type spin reorientation phase transition in SmCrO3

SmCrO₃ undergoes a discontinuous Morin type spin reorientation process due to discrete flipping of Cr³⁺ ions from the high temperature Γ₄ to low temperature Γ₁ configuration.

Retracted Article: Doping, strain, defects and magneto-optical properties of Zn1−xMnxO nanocrystals

High resolution transmission electron microscopic images of ZnO:Mn²⁺ nanoparticles, for (a) 10% Mn doping, showing defect free regular atomic arrangement, and (b) 20% Mn doping, irregular lattice planes with significant defects. (c) Digital photograph of liquid suspension of ZnO:Mn²⁺ nanocrystals under UV lamp. (d) MH loop of ZnO:Mn²⁺ nanoparticles.

Implication of local moment at Ti and Fe sites for the electrical and magneto-transport properties of degenerate semiconducting Ti₁-xFexO₂-d epitaxial films

We have investigated the effect of local magnetic moment on the electrical and magneto-transport properties of thin films of the degenerate semiconductor Ti(1-x)Fe(x)O(2-d) (x = 0,0.04). The electrical measurements of these films reveal high temperature metallic behavior and resistivity minima. The behavior below the resistivity minimum temperature is ascribed to Kondo like scattering. The coupling between the local moment and the charge carriers is reflected in the magnetoresistance measurements in these films. This work indicates competition between the magnetic ordering mechanism by J(RKKY) and the moment screening mechanism by J(Kondo). Accordingly the role of carrier density in achieving the magnetic ordering in such materials either by defect engineering or by transition metal doping is discussed.

Effect of non-magnetic impurities on the magnetic states of anatase TiO₂

The electronic and magnetic properties of TiO₂, TiO₁.₇₅, TiO₁.₇₅N₀.₂₅, and TiO₁.₇₅F₀.₂₅ compounds have been studied by using ab initio electronic structure calculations. TiO₂ is found to evolve from a wide-band-gap semiconductor to a narrow-band-gap semiconductor to a half-metallic state and finally to a metallic state with oxygen vacancy, N-doping and F-doping, respectively. The present work clearly shows the robust magnetic ground state for N-and F-doped TiO₂. The N-doping gives rise to a magnetic moment of ~ 0.4 μ(B) at the N site and ~ 0.1 μ(B) each at two neighboring O sites, whereas F-doping creates a magnetic moment of ~ 0.3 μ(B) at the nearest Ti atom. Here we also discuss the possible cause of the observed magnetic states in terms of the spatial electronic charge distribution of Ti, N, and F atoms responsible for bond formation.

Inspection of multiferroicity in BiMn(2-x)Ti(x)O(5) ceramics through specific heat and Raman spectroscopic studies

Inspection of multiferroicity in BiMn(2 - x)Ti(x)O(5) (0 ≤ x ≤ 0.30) (BMTO) ceramics is performed through specific heat and Raman spectroscopic studies. Thermal variation of specific heat (C) (in the absence and presence of fixed magnetic fields up to 14 T) and Raman spectra of BMTO are presented. In the temperature variation of C, a remarkable anomaly at the antiferromagnetic (AFM) ordering temperature (T(N) ∼ 39 K) is observed in all samples. Pure BiMn(2)O(5) (for x = 0.0) exhibits a larger specific heat anomaly at T(N) compared to that of Ti substituted samples, both in the presence and absence of external magnetic fields. The excess specific heat (ΔC) versus T clearly illustrates appreciable anomalies at ∼ 86 and ∼ 120 K in Ti doped samples related to the magnetic and dielectric transitions, respectively. The low temperature specific heat (LTSH) data indicate a considerably improved ferromagnetic contribution in samples with higher Ti concentration (x > 0.15). The Raman spectra of the doped samples at different fixed temperatures validate the strong electron-phonon coupling corresponding to the observed magnetism and increased harmonicity at dielectric transitions.

Growth and properties of pulsed laser deposited thin films of Fe(3)O(4) on Si substrates of different orientation

Fe(3)O(4) thin films were prepared by pulsed laser deposition on Si substrates of different orientations: (111), (100) and (110). X-ray diffraction studies revealed the spinel cubic structure of the films with preferential (111) orientation independent of the substrate orientation. Raman spectroscopy suggests the single-phase growth of Fe(3)O(4) films on these substrates, with minimum full width at half maxima being observed for the film grown on Si(111) substrate. These samples exhibit room-temperature ferromagnetism, as observed by magnetization hysteresis. The magnetization in these films saturates at a magnetic field value of approximately 0.2 T.

High temperature ferromagnetism with a giant magnetic moment in transparent co-doped SnO(2-delta)

The occurrence of room temperature ferromagnetism is demonstrated in pulsed laser deposited thin films of Sn(1-x)Co(x)O(2-delta) (x<0.3). Interestingly, films of Sn(0.95)Co(0.05)O(2-delta) grown on R-plane sapphire not only exhibit ferromagnetism with a Curie temperature close to 650 K, but also a giant magnetic moment of 7.5+/-0.5 micro(B)/Co, not yet reported in any diluted magnetic semiconductor system. The films are semiconducting and optically highly transparent.