Magnetic anisotropy and magnetostriction in cobalt-ferrite with lattice deformation

Magnetic anisotropy (MA) energy induced by uniform lattice deformation is calculated for cobalt-ferrites Fe(Co-Fe)₂O₄ (CFOs) by using an electron theory for down-spin t_2g electrons of Co²⁺ ions in CFOs. It is shown that the MA energy depends nonlinearly and asymmetrically on the uniform lattice deformation. By comparing the calculated results with those obtained in the phenomenological theory at the small lattice deformation limit, values of the magnetoelastic coefficients B₁ and B₂ have been evaluated. These values semi-quantitatively agree with the experimental ones. A non-trivial appearance of crystal-field potentials produced by the uniform trigonal lattice deformation is crucial to understand the large negative value of B₂. (paper)