Temperature dependence of the first-and second-order cubic anisotropy constants in EuO

The temperature dependence of the first-and second-order cubic anisotropy constants in EuO has been determined from ferromagnetic-resonance measurements on spherical singledomain, single-crystal samples. The observed dependence of K₁ is largely explained by a single-ion interaction. The constant K₂ is observed to change sign at ~1/2TC and its temperature dependence cannot be explained by just a single-ion interaction. The data have been analyzed by including the dipolar and pseudodipolar terms obtained by Kasuya and Tachiki in extending Van Vleck's calculation to third order. Very good agreement is obtained. The crystal-field parameters determined are b₄=2.3×10^-3 cm^-1 /ion and b₆=0.2×10^-3 cm^-1 /ion. It is found that pseudodipolar contributions are important with nearest-and next-nearest-neighbor contributions of 1.35 and 2.5 respectively, expressed in units of the corresponding pure magnetic dipolar term. The measured angular dependence of the resonance field has been analyzed including terms to second order in the ratio of the anisotropy to Zeeman energies. The values of K₁M and K₂M at 4.2 K are -247.5 ±{} 2.5 and 82 ±{} 10 Oe, respectively.