The exchange interaction and magnetic anisotropy in yttrium-iron garnets with small quantity of Sm$^{3+}$-ions

The magnetic anisotropy of five monocrystals in the yttrium iron-garnet system Y$3_x$Sm$_x$Fe$_5$E$_12$, where x = 0.0, 0.01%, 0.1%, 0.2%, and 0.5% is studied by means of ferromagnetic resonance. At temperatures from 10 to 90°C, the experimental values of К vary with temperature as 1/T$^{3}$. It is proposed that in this temperature region, the crystalline field acting on the Sm$^{3+}$ ions is basically cubic in structure. For a compound with x = 0.2%, the strength of the exchange field of approximately 47.6°K is found at a temperature of approximately 15°K acting from the Fe$^{3+}$ ions to the Sm$^{3+}$ ions. In a single-ion approximation at 0°K, the first and second theoretical anisotropy constants are computed, and are found to be in satisfactory agreement with experimentally found values of K1 and K2. It is concluded that anisotropy of dilute samarium garnets is basically single-ion in nature.