LOW-TEMPERATURE MAGNETIZATION AND SPIN-WAVE EXCITATION IN NANOCRYSTALLINE FERROMAGNETS

Magnetization measurements in the temperature range 1.5-300 K have been made on two series of samples of nanocrystalline ferromagnets: Fe60Co30Zr10 and Fe73.5CuNb3Si13.5B9. It was found that at low temperatures magnetization decreases in accordance with the Heisenberg-model prediction for both series of samples. The coefficients B and C were obtained by fitting M(s)(T) to two terms, T3/2 and T5/2, from the Bloch law. It is shown that for both series of samples the B and C coefficients are larger in the amorphous state than in the nanocrystalline state, larger values of spin-wave stiffness constants D were obtained in nanocrystalline FeCoZr samples with grain size d < 40 nm than in the amorphous state; with increasing grain size a much larger value for D was observed for nanocrystalline FeCoZr with a grain size of 140 nm. The results present a reasonable agreement with predictions for nanocrystalline materials with two or three different magnetic phases.