Magnetic Structure of Ground and Field Induced Ordered States of Low-Dimensional γ-CoV₂O₆

Abstract

The structural and magnetic properties of γ-CoV 2 O 6 low-dimensional magnetic oxide have been investigated with an emphasis on its magnetic structure. Our main results have been obtained by powder neutron diffraction measurements carried out under magnetic fields of 0, 0.52, and 1 T, corresponding to the antiferromagnetic, ferrimagnetic, and ferromagnetic configurations of the magnetic moments. The magnetic moments are not collinear, but lie mostly along the b direction (i.e., inside structural edge-sharing CoO 6 chains), which corresponds to the experimental easy magnetization axis. In the ground state, the moments are ferromagnetically ordered along the b and c directions, and antiferromagnetically ordered along a. The ferromagnetic sheets (bc plane) containing the chains are separated by nonmagnetic sheets containing VO 6 octahedra and VO 4 tetrahedra. The ground state magnetic structure can be described in a (4a, 2b, c) supercell using two antiferromagnetic propagation vectors k AF1 = (1/2, 0, 0) and k AF2 = (1/4, 1/2, 0). The ferri-and ferromagnetic structures are characterized by k Fi = (1/3, 0, −1/3) and k = (0, 0, 0) propagation vectors, respectively. These results are in agreement with macroscopic magnetic measurements performed on single crystals.

Unconventional magnetic phase separation in γ-CoV2O6

“…This leads to a very small orbital contribution to the total moment in γCVO, as revealed by X-ray magnetic circular dichroism (XMCD) spectroscopy and theoretical calculations 29,31 . The result is a global average spin moment of ∼ 3.2 µ B /Co, mainly pointing along the b-axis, in agreement with magnetization measurements 18,19,21,26 . We point out that the 2k solution is inconsistent with this value.…”

“…These data (not shown here) confirm the propagation vector k 1 = (0.5, 0, 0) of the magnetic structure found by Kimber et al 19 and Lenertz et al 21 , but we did not find peaks corresponding to the second propagation vector (0.25, 0.5, 0) proposed in Ref. 21. Furthermore, we find a magnetic Bragg peak at Q 1.03 Å −1 in our powder diffraction profiles ( Fig.…”

Magnetic and magnetocaloric properties of quasi-one-dimensional Ising spin chain CoV2O6

“…17 Neutron diffraction studies have revealed that CoV 2 O 6 compounds undergo successive field-induced transitions from AFM to ferrimagnetic (FI) state at H c1 and FI to FM state at H c2 . 13,16,21 At 2 K, the values of saturation magnetization are 4.5 and 2.9 µ B /Co ion, respectively for α and γ phases which are close to those reported for the single crystals. 12,21 Though the value of saturation magnetization for the γ phase is close to the expected spin-only moment (3.0 µ B /Co) of high-spin Co 2+ , the huge difference between the observed saturation moment and expected spin-only moment in α phase indicates a strong spin-orbit coupling in this system.…”

“…The significant difference in spin-orbit coupling between two polymorphs of CoV 2 O 6 has been attributed to the Co-Co distance and the local deformation of the octahedral oxygen environment around the Co 2+ ion. 11,21,23 CoO 6 octahedron is highly distorted in α phase whereas it is almost regular in γ phase. Due to this large distortion of CoO 6 octahedron, the spin-orbit coupling is quite strong in α phase.…”

“…The easy axis is along the c axis in α phase 12,13 while it is along the chain direction in γ phase. 20,21 As V ions are in nonmagnetic pentavalent state, the magnetic contribution comes from the Co 2+ ion. The intrachain magnetic interaction is strong and ferromagnetic in nature while the chains are weakly coupled via antiferromagnetic interaction.…”