Magnetic, structural, and thermal properties of CoV₂O₄

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.

Magnetic Frustration Driven by Itinerancy in Spinel CoV2O4

Localized spins and itinerant electrons rarely coexist in geometrically-frustrated spinel lattices. They exhibit a complex interplay between localized spins and itinerant electrons. In this paper, we study the origin of the unusual spin structure of the spinel CoV₂O₄, which stands at the crossover from insulating to itinerant behavior using the first principle calculation and neutron diffraction measurement. In contrast to the expected paramagnetism, localized spins supported by enhanced exchange couplings are frustrated by the effects of delocalized electrons. This frustration produces a non-collinear spin state even without orbital orderings and may be responsible for macroscopic spin-glass behavior. Competing phases can be uncovered by external perturbations such as pressure or magnetic field, which enhances the frustration.

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.

Orbital Glass State of the Nearly Metallic Spinel Cobalt Vanadate

Strain, magnetization, dielectric relaxation, and unpolarized and polarized neutron diffraction measurements were performed to study the magnetic and structural properties of spinel Co_{1-x}V_{2+x}O_{4}. The strain measurement indicates that, upon cooling, ΔL/L in the order of ∼10^{-4} starts increasing below T_{C}, becomes maximum at T_{max}, and then decreases and changes its sign at T^{*}. Neutron measurements indicate that a collinear ferrimagnetic order develops below T_{C} and upon further cooling noncollinear ferrimagnetic ordering occurs below T_{max}. At low temperatures, the dielectric constant exhibits a frequency dependence, indicating slow dynamics. These results indicate the existence of an orbital glassy state at low temperatures in this nearly metallic frustrated magnet.