Diagonal and Nondiagonal Susceptibility of a Ferromagnetic Electron Gas

Abstract

The spatial dependence of the spin and charge response of a ferromagnetic metal is discussed by introducing the q-dependent spin and charge susceptibility to a magnetic field χmm(q) and χem(q), and the spin and charge susceptibility to a charge potential χme(q) and χee(q). The nondiagonal susceptibilities χme and χem are shown to be very important in ferromagnetic metals, since the effect of an impurity can be represented by the addition of both a charge Ze and spin S. Some of the essential features of neutron scattering experiments about impurities in ferromagnetic metals can be understood by properly including both the diagonal and nondiagonal susceptibilities.