Magnetoelectric Coupling through the Spin Flop Transition in Ni_{3}TeO_{6}

Hydrothermal Synthesis of Ni3TeO6 and Cu3TeO6 Nanostructures for Magnetic and Photoconductivity Applications

Despite great attention toward transition metal tellurates especially M₃TeO₆ (M = transition metal) in magnetoelectric applications, control on single phasic morphology-oriented growth of these tellurates at the nanoscale is still missing. Herein, a hydrothermal synthesis is performed to synthesize single-phased nanocrystals of two metal tellurates, i.e., Ni₃TeO₆ (NTO with average particle size ∼37 nm) and Cu₃TeO₆ (CTO ∼ 140 nm), using NaOH as an additive. This method favors the synthesis of pure NTO and CTO nanoparticles without the incorporation of Na at pH = 7 in MTO crystal structures such as Na₂M₂TeO₆, as it happens in conventional synthesis approaches such as solid-state reaction and/or coprecipitation. Systematic characterization techniques utilizing in-house and synchrotron-based characterization methods for the morphological, structural, electronic, magnetic, and photoconductivity properties of nanomaterials showed the absence of Na in individual particulate single-phase MTO nanocrystals. Prepared MTO nanocrystals also exhibit slightly higher antiferromagnetic interactions (e.g., T _N-NTO = 57 K and T _N-CTO = 68 K) compared to previously reported MTO single crystals. Interestingly, NTO and CTO show not only a semiconducting nature but also photoconductivity. The proposed design scheme opens the door to any metal tellurates for controllable synthesis toward different applications. Moreover, the photoconductivity results of MTO nanomaterials prepared serve as a preliminary proof of concept for potential application as photodetectors.

A New Cation‐Ordered Structure Type with Multiple Thermal Redistributions in Co 2 InSbO 6

Cation ordering in solids is important for controlling physical properties and leads to ilmenite (FeTiO₃) and LiNbO₃ type derivatives of the corundum structure, with ferroelectricity resulting from breaking of inversion symmetry in the latter. However, a hypothetical third ABO₃ derivative with R32 symmetry has never been observed. Here we show that Co₂InSbO₆ recovered from high pressure has a new, ordered‐R32 A₂BCO₆ variant of the corundum structure. Co₂InSbO₆ is also remarkable for showing two cation redistributions, to (Co_0.5In_0.5)₂CoSbO₆ and then Co₂InSbO₆ variants of the ordered‐LiNbO₃ A₂BCO₆ structure on heating. The cation distributions change magnetic properties as the final ordered‐LiNbO₃ product has a sharp ferrimagnetic transition unlike the initial ordered‐R32 phase. Future syntheses of metastable corundum derivatives at pressure are likely to reveal other cation‐redistribution pathways, and may enable ABO₃ materials with the R32 structure to be discovered.

Angular dependence of spin-flop transition in triangular lattice antiferromagnet Cu2(OH)3Br

We report angular dependence of spin-flop transition in triangular lattice antiferromagnet Cu₂(OH)₃Br by angle-dependent magnetization and ESR measurements. The results show that the antiferromagnetic easy magnetization axis is the diagonal direction (θ= 45°) of theac^*plane, i.e., the orientation of Cu1 spins based on the magnetic structure (2020Phys. Rev. Lett.125037204), whereas the spin-flop axis is thebaxis. A phenomenological model is proposed to describe the angle-dependent spin-flop transitions. Based on this model, Cu1 spins are sensitive to external magnetic field, while Cu2 spins are robust against to the field, showing partial decoupling. The model is expected to be used in other uniaxial antiferromagnets with a more general easy axis and complex spin-flop transitions.

High-Pressure Synthesis and Ferrimagnetism of Ni3TeO6-Type Mn2ScMO6 (M = Nb, Ta)

The corundum-related oxides Mn₂ScNbO₆ and Mn₂ScTaO₆ were synthesized at high pressure and high temperature (6 GPa and 1475 K). Analysis of the synchrotron powder X-ray diffraction shows that Mn₂ScNbO₆ and Mn₂ScTaO₆ crystallize in Ni₃TeO₆-type noncentrosymmetric crystal structures with space group R3. The asymmetric crystal structure was confirmed by second harmonic generation measurement. X-ray absorption near-edge spectroscopies indicate formal valence states of Mn²⁺₂Sc³⁺Nb⁵⁺O₆ and Mn²⁺₂Sc³⁺Ta⁵⁺O₆, also supported by the calculated bond valence sums. Both samples are electrically insulating. Magnetic measurements indicate that Mn₂ScNbO₆ and Mn₂ScTaO₆ order ferrimagnetically at 53 and 50 K, respectively, and Mn₂ScTaO₆ is found to have a field-induced magnetic transition.

Orbital-flop Induced Magnetoresistance Anisotropy in Rare Earth Monopnictide CeSb

The charge and spin of the electrons in solids have been extensively exploited in electronic devices and in the development of spintronics. Another attribute of electrons—their orbital nature—is attracting growing interest for understanding exotic phenomena and in creating the next-generation of quantum devices such as orbital qubits. Here, we report on orbital-flop induced magnetoresistance anisotropy in CeSb. In the low temperature high magnetic-field driven ferromagnetic state, a series of additional minima appear in the angle-dependent magnetoresistance. These minima arise from the anisotropic magnetization originating from orbital-flops and from the enhanced electron scattering from magnetic multidomains formed around the first-order orbital-flop transition. The measured magnetization anisotropy can be accounted for with a phenomenological model involving orbital-flops and a spin-valve-like structure is used to demonstrate the viable utilization of orbital-flop phenomenon. Our results showcase a contribution of orbital behavior in the emergence of intriguing phenomena.

The orbital degree of freedom can be as important as the charge and spin of the electron to the electronic phenomena. Here the authors show additional minimum in the angle-dependent magnetoresistance (MR) for the low temperature high magnetic field driven ferromagnetic state in CeSb which indicates the orbital flop induced MR anisotropy.

Anisotropy in the magnetic interaction and lattice-orbital coupling of single crystal Ni3TeO6

This investigation reports on anisotropy in the magnetic interaction, lattice-orbital coupling and degree of phonon softening in single crystal Ni₃TeO₆ (NTO) using temperature- and polarization-dependent X-ray absorption spectroscopic techniques. The magnetic field-cooled and zero-field-cooled measurements and temperature-dependent Ni L_3,2-edge X-ray magnetic circular dichroism spectra of NTO reveal a weak Ni-Ni ferromagnetic interaction close to ~60 K (T_SO: temperature of the onset of spin ordering) with a net alignment of Ni spins (the uncompensated components of the Ni moments) along the crystallographic c-axis, which is absent from the ab-plane. Below the Néel temperature, T_N~ 52 K, NTO is stable in the antiferromagnetic state with its spin axis parallel to the c-axis. The Ni L_3,2-edge X-ray linear dichroism results indicate that above T_SO, the Ni 3d e_g electrons preferentially occupy the out-of-plane 3d_3z²_−r² orbitals and switch to the in-plane 3d_x²_−y² orbitals below T_SO. The inherent distortion of the NiO₆ octahedra and anisotropic nearest-neighbor Ni-O bond lengths between the c-axis and the ab-plane of NTO, followed by anomalous Debye-Waller factors and orbital-lattice in conjunction with spin-phonon couplings, stabilize the occupied out-of-plane (3d_3z²_−r²) and in-plane (3d_x²_−y²) Ni e_g orbitals above and below T_SO, respectively.