Magnetic alloys, their electronic structure and micromagnetic and microstructural models

We present a selective review of electronic structure calculations for ferromagnetic transition metal alloys. This is work based on the spin density functional theory of the inhomogeneous electron gas which we also discuss briefly. These calculations can be used to provide estimates, from 'first principles', of the alloys' characteristic properties such as the saturation magnetization, M-s, and the exchange, A, and anisotropy, K, constants as well as their Curie temperatures, T-c, which are all important quantities for the micromagnetic modelling of these materials. The electronic reasons for the simple structure of Slater-Pauling curves of M-s versus the number of valence electrons are given. Anisotropy constants, K, can be evaluated only when relativistic effects upon the electronic motion are included. We review the theory of finite-temperature metallic magnetism and highlight how the electronic structure of metals and alloys in their paramagnetic states can still exhibit a local spin polarization originating from the 'local moment' spin fluctuations which are excited as the temperature is raised. Finally we show how an alloy's magnetic state can sharply influence the types of ordered arrangements that the atoms form and conversely how the type of compositional structure can affect M-s and K. We include a discussion of how the compositional structure can be described in terms of static 'concentration waves'. We illustrate the approach by outlining our recent case studies of two iron-rich alloy systems, FeV and FeAl.