Magnetism of Disordered Alloys

Abstract

Chapter 8 is concerned with the magnetism of the Slater–Pauling (SP) curves for binary 3d transition-metal alloys. We first argue the SP curves from a view point of the rigid band model. Next we introduce the coherent potential approximation (CPA) to describe the electronic structure of the disordered alloys, and show that the Hartree–Fock CPA scheme with reduced Coulomb interactions successfully explains the SP curves in the concentrated region. We then extend the theory to the finite temperatures using the SSF (the dynamical CPA in the high temperature approximation). The alloys such as the Ni–Cu, Ni–Mn, and Fe–Ni show strong disturbance of local magnetic moments (LM’s) due to the local atomic configuration, which is referred as the local environment effects (LEE). We present theories of the LEE both at the ground state and at finite temperatures. With use of these theories, we elucidate the LEE on the LM’s, the formation of the SG, the SP curves, as well as the Curie temperature SP curves in 3d transition metal alloys. The finite-temperature theory of the LEE relies on the distribution of LM’s, so that the spin arrangement in the real space is not clear. We therefore introduce the molecular-dynamics (MD) approach to the disordered magnetic alloys and explain the complex magnetic structure in Fe–Cr alloys as an example.