Soft Magnetic Properties of Ni-Fe-Nb Alloy Films with Nearly 50 wt% Ni Concentration

The relation between soft magnetic properties and local anisotropy fluctuation, which is strongly connected with the film microstructure, was systematically examined for Ni-Fe-Nb alloy films with nearly 50 wt% Ni. According to the micromagnetic ripple theory of Hoffmann, the effective magnetic anisotropy U
^eff
in each of the grains decreases drastically with increases in the number of grains N within the coupling volume. Experimental results showed that the local anisotropy fluctuation in Ni-Fe-Nb alloy films depends heavily on U
^eff
/K
u
, and decreases with decreasing U
^eff
/K
u
. Therefore, to realize high initial permeability in such films, it is necessary to increase N within the coupling volume by decreasing the grain size. In the cae of Ni-Fe-Nb alloy films, the grain size must be decreased to less than 200 Å in order to obtain a high initial permeability more than 2000.