Electronic states and possible origin of the orbital-glass state in a nearly metallic spinel cobalt vanadate: An x-ray magnetic circular dichroism study

Abstract

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.

Local Magnetic States of the Weakly Ferromagnetic Iron-Based Superconductor Sr2VFeAsO3−δ Studied by X-ray Magnetic Circular Dichroism

“…Still, the XAS and XMCD spectra are similar to what obtained for compounds where V atoms are octahedrally coordinated by O atoms. 12) By comparing the present XMCD spectra with cluster-model calculation, 12) we obtain an approximate value for the V magnetic moment of 0.3 µ B at H = 10 T. Then from Fig. 2(c), one finds the remnant magnetic moment of 3(±2) × 10 −3 µ B , which is consistent with the present SQUID measurement.…”

Rational Design of Spinel Cobalt Vanadate Oxide Co2VO4 for Superior Electrocatalysis

“…Given that the valence states of Co cations in Co 2 VO 4 and CoO are both +2, this peak‐shift indicates the different spin configurations between Co 2 VO 4 and CoO. It should be noted that the electronic configuration of T d ‐site Co 2+ in Co 2 VO 4 is t 2 3 e 4 (Figure S10, Supporting Information) . To examine the detailed spin state of O h ‐site Co 2+ in Co 2 VO 4 , simulation of the experimental EELS spectra was carried out (Figure 3b, Figure S11 and Table S2, Supporting Information), assuming that the O h ‐site Co 2+ ions take either the HS or the LS state.…”

Complete description of the magnetic ground state in spinel vanadates

“…3(c)). This is a counter intuitive yet explainable trend-as (a) V magnetic moment calculated using LSDA (light blue), LSDASF (green), LSDA+U (pink) and LSDA+USF (red) compared with corresponding experimental (cyan) values [5,21,23,24,27] for M nV2O4, F eV2O4 and CoV2O4. The on-site Hubbard U parameter is set equal to 2.7 eV for all materials.…”

“…As for the value of the angle between the V and A site spins, consistent with the experimental observations our results show that the A site moment is collinear with the c-axis in presence or absence of the source term in the functional. On the other hand, the canting angle of the V spins is highly functional dependent in that LSDA+U functional, in presence of spin-orbit coupling, leads to a small canting angle of 19 Magnitude of the moment: As discussed in the introduction, experimental measurements via neutron diffraction [5,23,27], XMCD [24] etc. on spinel vanadates report a small moment on the V atoms in all these compounds;…”

“…Furthermore, XMCD measurements performed on MnV 2 O 4 and FeV 2 O 4 reveal a very small value of the orbital moment [22] indicating the V moment is primarily spin in character [34], and so the cancellation of the spin-moment by the orbital moment cannot be the reason behind this reduction in the moment. As for the moment on the A-site is concerned, all experiments report a large moment [5,[22][23][24].…”