Electrical conduction in ferromagnetic metals
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Abstract
Experiments are reported on the electrical-conduction properties of a large number of binary and ternary alloys based on either nickel or iron. The solutes represent the elements that can be dissolved in nickel or iron at a concentration of 3 at %. At 4.2 K the resistivity, the resistivity anisotropy, the normal and the anomalous Hall effect have been measured. The results were analysed in terms of a two-current model. In this model two mutually independent currents are associated with the two possible directions of the electron spin, viz. the majority- and the minority-spin direction. For 17 solutes in nickel and 20 solutes in iron we determined the two specific residual resistivities corresponding to the two currents. The trends among the specific resistivities found can be explained in terms of existing data on magneticmoment disturbances around solute metals in the ferromagnetic matrix. It was found that a simple phenomenological description of the resistivity anisotropy in nickel- or iron-based alloys can be given in terms of the twocurrent model. It appears that the anisotropy effect is mainly due to one of the two bands, viz. the majority-spin band in nickel and the minority-spin band in iron. In nickel-based alloys the anomalous Hall effect, too, can satisfactorily be described in terms of the two-current model, taking into account the mechanisms of skew scattering and of side displacement. The skew-scattering angles and the coefficients for side displacement in the two bands were determined for different solutes in nickel. In the majority-spin band of nickel both the skew-scattering term and the side-displacement term are negative, in the minority-spin band of nickel both terms are found to be positive. The limits of validity of the two-current model were observed in a study o the normal Hall effect in nickel-based alloys. It was found that within the majority-spin band of nickel the Hall coefficient varies systematically with the mean free path of the current carriers.