Conduction-electron-spin polarization of ferromagnetic4fand5fsystems:T-matrix approach

We present a calculation of the conduction-electron-spin polarization P(T,n) for ferromagnetic f systems as a function of temperature T and band occupation n (0{≤}n{≤}2, s band). For 4f systems such as EuO and EuS, which are characterized by a ferromagnetic s-f exchange, the polarization P is complete for very small n, where the value of the critical band filling, at which depolarization sets in, depends on T. At constant temperature the polarization exhibits a minimum at about n=0.5 and a relative maximum for the exactly-half-filled conduction band (n=1). The special case T=0 and n=1 leads again to totally polarized conduction electrons. The temperature dependence of P explains recently performed field-emission and photoemission data. For 5f systems such as USe, with antiferromagnetic s-f exchange, P is always negative without any special feature at n=1. The (T,n) dependence of the conduction-electron-spin polarization is a direct consequence of the corresponding behavior of the quasiparticle density of states, which is therefore discussed in detail.