Growth-Induced Magnetic Anisotropy of Epitaxial Films of Mixed Garnets Containing Europium

Abstract

We have measured the ferromagnetic resonance of three garnet films with the approximate composition ${R}_{2}\mathrm{Eu}{\mathrm{Fe}}_{4}{\mathrm{O}}_{12}$, where $R=\mathrm{Y}\mathrm{or}\mathrm{Lu}$ and $M=\mathrm{Al}\mathrm{or}\mathrm{Ga}$, grown by liquid-phase epitaxy on 001 and {111} gadolinium gallium garnet substrates. The anisotropy has a growth-induced component which anneals out at 1250\ifmmode^\circ\else\textdegree\fi{}C. Measurements from $0.04{T}_{C}$ to $0.92{T}_{C}$ on a {111} film with ${T}_{C}=404 \ifmmode^\circ\else\textdegree\fi{}$K show that this component is proportional to the calculated uniaxial anisotropy of a ${\mathrm{Eu}}^{3+}$ ion in garnet, up to $0.75{T}_{C}$. This proportionality is predicted by the site-preference theory of the growth-induced anisotropy. The calculation is based on the Wolf-Van Vleck model of europium iron garnet, extended to include spin-correlation effects on the $d$ sublattice in a heuristic manner. Anisotropic exchange is found to be the dominant source of the anisotropy. We find site preferences of about 20% in all three films. The calculation also accounts reasonably well for the temperature dependence of the magnetostriction of europium iron garnet.