Temperature-dependent anisotropy effects on FMR and magnetization of FePt2 and CoPt3 nanocrystals

Abstract We present magnetization isotherms and 9 GHz ferromagnetic resonance (FMR) spectra recorded on powders containing 6 nm -diameter nanocrystals, prepared by a high-temperature organometallic route. Upon lowering the temperature from 400 K towards the blocking temperature, T b ≈50 K , deviations from Langevin isotherms and shifts of the FMR field occur, which for the first time are consistently explained by introducing a uniaxial anisotropy which, for both CoPt 3 and FePt 2 , strongly decay with the 6th power of the particle moments μ p ( T ).