Influence of the Microstructure on the Magnetization Processes in Nanocrystalline Fe73.5Cu1Nb3Si13.5B9

The correlation between the magnetization processes and the microstructure of nanocrystalline Fe73.5Cu1Nb3Si13.5B9 is investigated. After annealing the originally amorphous samples above the crystallization temperature the coercivity Hc, the initial susceptibility χo, and the Rayleigh constant αR change their values with increasing annealing temperature by several orders of magnitude due to a change of the magnetization process. This occurs without any significant change in the grain size, D ≈ 12 nm, of the nanocrystalline FeSi grains (20 at% Si) in the samples. For lower annealing temperatures, TA ≦ 853 K, irreversible Bloch wall movements are found, which can be described by the statistical potential theory. For annealing temperatures above 853 K the mobility of the Bloch walls is reduced due to pinning caused by Fe–B precipitations. As a result reversible rotational magnetization processes dominate. This is also demonstrated by domain pattern observations by the magnetooptical Kerr effect. Theoretical values for Hc, χo, and αR correlate well with the experimental data.