The Microstructure of a Permalloy in the K State

The microstructure of a 2.4 at.-% molybdenum permalloy annealed to produce the K state was investigated on the atomic scale by field-ion microscopy.It was found that the matrix is well ordered, possessing theL1₂ superlattice Ni₃Fe, and the molybdenum atoms exhibit a tendency towards clustering.In addition the sparse heterogenous precipitation of a phase which probably contains nickel and iron, in addition to molybdenum, was observed. No microstructural inhomogeneity was observed which could account for the anomalous resistivity increase characteristic of the K state and it is therefore concluded that the changes in the electronic band structure which take place on annealing are such as to decrease the concentration offree carrier electrons.