Light-induced magnetic anisotropy in Co-doped garnet films

Light-induced uniaxial magnetic anisotropy characterized by amplitude, times of creation τ₁, and a vanishing τ₂ was studied. The investigation was performed on YIG (yttrium iron garnet):Co,Ca,Ge liquid-phase epitaxy films using a very sensitive method---observation of changes of magnetic domain structure with a different in-plane magnetization component induced by linearly polarized light pulses. An argon laser (λ=488 nm) was used. The effective field HL was introduced to describe the photoinduced uniaxial magnetic-anisotropy amplitude. These domain changes were studied within the temperature range of 160--300 K. With an increase in temperature an increase in τ₁, a decrease in τ₂, and a drastic decrease in HL were found. The appearance of the photoinduced anisotropy is explained by light-induced rearrangement of strongly anisotropic Co²⁺ octahedral ions. A microscopic model was proposed where ion rearrangement is connected with electron excitations into the conducting band. Both thermal and light-induced excitations were discussed. Numerical and analytical solutions of kinetic equations describing the model are discussed. The dynamics of light-induced magnetic anisotropy both uniaxial and cubic is analyzed.