Strain, magnetization, and unpolarized and polarized neutron diffraction measurements were performed to study the magnetic and structural properties of spinel CoV2O4. Magnetostriction measurements indicate that a subtle distortion of the crystal along the direction of magnetization, ∆L/L ∼ 10 −4 , exists and varies from elongation to contraction in a second order fashion upon cooling. Unpolarized and polarized single-crystal neutron experiments indicate that upon cooling the ferrimagnetic structure changes from collinear to noncollinear at T ∼ 90 K, where the elongation of the crystal is maximized. These results imply the existence of an orbital glassy state in the nearly metallic frustrated magnet CoV2O4.
We have investigated the orbital states of the orbital-glassy (short-range orbital ordered) spinel vanadate Co1.21V1.79O4 using x-ray absorption spectroscopy (XAS), x-ray magnetic circular dichroism (XMCD), and subsequent configuration-interaction cluster-model calculation. From the sign of the XMCD spectra, it was found that the spin magnetic moment of the Co ion is aligned parallel to the applied magnetic field and that of the V ion anti-parallel to it, consistent with neutron scattering studies. It was revealed that the excess Co ions at the octahedral site take the trivalent low-spin state, and induce a random potential to the V sublattice. The orbital magnetic moment of the V ion is small, suggesting that the ordered orbitals mainly consists of real-number orbitals.
We perform ultrasound velocity measurements on a single crystal of nearly-metallic spinel Co1.21V1.79O4 which exhibits a ferrimagnetic phase transition at TC ∼ 165 K. The experiments reveal a variety of elastic anomalies in not only the paramagnetic phase above TC but also the ferrimagnetic phase below TC, which should be driven by the nearly-itinerant character of the orbitally-degenerate V 3d electrons. In the paramagnetic phase above TC , the elastic moduli exhibit elastic-mode-dependent unusual temperature variations, suggesting the existence of a dynamic spin-cluster state. Furthermore, above TC, the sensitive magnetic-field response of the elastic moduli suggests that, with the negative magnetoresistance, the magnetic-field-enhanced nearly-itinerant character of the V 3d electrons emerges from the spin-cluster state. This should be triggered by the inter-V-site interactions acting on the orbitally-degenerate 3d electrons. In the ferrimagnetic phase below TC , the elastic moduli exhibit distinct anomalies at T1 ∼ 95 K and T2 ∼ 50 K, with a sign change of the magnetoresistance at T1 (positive below T1) and an enhancement of the positive magnetoresistance below T2, respectively. These observations below TC suggest the successive occurrence of an orbital glassy order at T1 and a structural phase transition at T2, where the rather localized character of the V 3d electrons evolves below T1 and is further enhanced below T2.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.