98DENSITY FLUCTUATIONS AND FIELD-DEPENDENT SUSCEPTIBILITY IN NEARLY FERROMAGNETIC ALLOYS

When a large magnetic field is applied to a nearly ferromagnetic metal, the effective field on an up spin differs from that on a down spin; hence, their responses to the field also differ. Thus, density fluctuations accompany spin fluctuations. The response to a small oscillating longitudinal magnetic field is calculated by solving coupled equations for the oscillating magnetization and particle density. For pure metals, we extend Wohlfarth's result to nonzero frequency and wave number. Local density fluctuations are particularly important in the impurity problem. Here Lederer and Mills's results are extended to high fields. In particular, we calculate the static susceptibility to second order in an applied field. The result is written in terms of band parameters of the host metal. This result allows us to estimate the field dependence of the alloy susceptibility from measurements on pure metals. The case of Ni in Pd is discussed as an example. © 1969 The American Physical Society.