Local structure and magnetic structure of spinel oxide MnV₂O₄ observed by Mössbauer spectroscopy

Mössbauer spectroscopic study has been conducted on a spinel oxide MnV₂O₄ by using a 1mol% ⁵⁷Fe-substituted polycrystalline specimen as an absorber. The substituted ⁵⁷Fe ions occupy both the A- and B-sites as Fe²⁺ and Fe³⁺ with a high-spin state, respectively. The Mössbauer spectra clarify the local crystallographic structure and the magnetic structure of both the Mn²⁺ ion at the A site and the V³⁺ ion at the B site. The spectra in the magnetically ordered phase were analyzed using a mixed magnetic and quadrupole Hamiltonian, and the magnetic structures were obtained by calculating the electric field gradient (EFG) axes with respect to the crystallographic axes. Below T_c ∼ 60K, a ferrimagnetic order along the 〈001〉_c axis was observed in the cubic phase, whereas below T_s ∼ 50K, a simultaneous transition into a tetragonal phase and a canted ferrimagnetic state were observed. In this tetragonal phase, the V³⁺ spins were found to be almost within the tetragonal ð110 Þ_t [cubic (100)_c] plain and inclined by 52° from the c-axis, while the Mn²⁺ spins were found to be along the c-axis opposite to the V³⁺ spins.