A-type antiferro-orbital ordering with I4(1)/a symmetry and geometrical frustration in the spinel vanadate MgV2O4

Understanding the correlation between orbital degree of freedom, lattice-striction and magneto-dielectric coupling in ferrimagnetic Mn1.5Cr1.5O4

Dielectric anomaly observed in cubic Mn_1.5Cr_1.5O₄around ferrimagnetic ordering temperature (T_N) suggests a possible magneto-dielectric coupling in the system. This report confirms the presence of a weak but significant magneto-dielectric coupling in the system. Theab initiocalculations show a band gap of around 1.2 eV, with Fermi-level closer to the conduction band. The major features of conduction band nearest to the Fermi-level correspond tod_xzandd_3z²_-r²orbitals of Mn³⁺ion. Temperature-dependent neutron diffraction results show a rapid decay in structural parameters (lattice-striction and transition metal-oxygen bond length) aroundT_N.We confirmed that these changes in structural parameters atT_Nare not related to structural transition but the consequences of orbital-ordering of Mn³⁺. The rapid decay in transition metal-oxygen bond length under internal magnetism of the system shows that magnetism could certainly manipulate the electric dipole moment and hence the dielectric constant of the system. Magneto-striction acts as a link between magnetic and dielectric properties.

Tailoring magnetism in spinel vanadate CoV2O4epitaxial thin films

Near itinerant cubic bulk CoV₂O₄is at variance with other spinel vanadates by not showing orbital ordering down to low temperature, albeit it displays fragile anomalies related to spin, and lattice structure, signaling a spin/orbital glass transition around 95 K. We investigate tetragonal-like epitaxial CoV₂O₄films on SrTiO₃and (La_0.3Sr_0.7)(Al_0.65Ta_0.35)O₃substrates that exhibit pronounced signature of spin reorientation transition from toa/bplane around 90 K unlike its bulk counterpart. Using in-plane and out-of-plane magnetic measurements, we demonstrate the intricate link between Co²⁺and V³⁺sublattice magnetizations that give rise to anisotropic magnetic switching. In-plane magnetic measurements reveal a wasp-waist shapedM(H) loop below reorientation transition temperature, while the out-of-plane follows antiferromagnet-likeM(H) response. The wasp-waist shaped feature could be linked to in-plane spin-canted (anti)ferromagnetism induced by canting away of V-spins away from antiferromagnetically coupled Co-spin direction below reorientation transition temperature. Further, we uncover the evidence for slow relaxation over a period of ∼10⁴ s at 20 K and memory effect that indicates the possible existence for magnetic glassy phase in the low temperature regime. Using epitaxial strain as a control knob, our results inspire future study to manipulate orbital states, spin texture and itinerant electron character in tailored CoV₂O₄films away from cubic lattice symmetry.

Spin-Orbital Correlated Dynamics in the Spinel-Type Vanadium Oxide MnV_{2}O_{4}

We investigate the magnetic dynamics in the spinel-type vanadium oxide MnV_{2}O_{4}. Inelastic neutron scattering around 10 meV and a Heisenberg model analysis have revealed that V^{3+} spin-wave modes exist at a lower-energy region than previously reported. The scattering around 20 meV cannot be reproduced with the spin-wave analysis. We propose that this scattering could originate from the spin-orbital coupled excitation. This scattering is most likely attributable to V^{3+} spin-wave modes, entangled with the orbital hybridization between t_{2g} orbitals.

Ferro-to-antiferro orbital variation in vanadium spinel Fe1-xMnxV2O4

We have synthesized the Fe(1-x)Mn(x)V(2)O(4) (0 ≦ x ≦ 1) system, and have investigated its structural and magnetic properties through synchrotron powder diffraction, magnetization and specific heat measurements. We have examined the local distortion for both the FeO(4) tetrahedron and VO(6) octahedron on the basis of structural refinements using the synchrotron diffraction data. We found that the behaviour of these local distortions and the temperature dependent magnetization changes continuously with respect to the Mn(2+) concentration, x. The local distortion of the FeO(4) tetrahedron derived from the orbital order of the x(2)-y(2) type below the ferrimagnetic transition temperature becomes smaller for x ≦ 0.6, and is absent for x > 0.6. The ferro-orbital order, leading to compressed local distortion of VO(6) below the non-collinear ferrimagnetic order temperature, is gradually suppressed with increasing x and changes to the antiferro-orbital order for x > 0.6, for which the long range orbital order of Fe(2+) disappears. We suggest that the two types of V(3+) orbital orders are strongly correlated with the non-collinear magnetic order, and that the ferro-orbital order is possibly stabilized by the orbital degrees of freedom of the Fe(2+) ions located at the A-site.