Light-induced magnetic anisotropy in Co-doped garnet films

Abstract

Light-induced uniaxial magnetic anisotropy characterized by amplitude, times of creation ${\ensuremath{\tau}}_{1},$ and a vanishing ${\ensuremath{\tau}}_{2}$ 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 $(\ensuremath{\lambda}=488$ nm) was used. The effective field ${H}_{L}$ 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 ${\ensuremath{\tau}}_{1},$ a decrease in ${\ensuremath{\tau}}_{2},$ and a drastic decrease in ${H}_{L}$ were found. The appearance of the photoinduced anisotropy is explained by light-induced rearrangement of strongly anisotropic ${\mathrm{Co}}^{2+}$ 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.