The Prediction of Structure-Type and Magnetic Properties of Iron-Based Alloys

Abstract

The search for new magnetic phases has centred on the rare-earth-iron pseudo-binaries with non-cubic crystal structures and the ternary borides. We show that the ordering of the known empirical structural data base within a limited number of two-dimensional structure maps helps focus the search for iron based alloys with a particular structure-type. In particular, the tetragonal binary structure-types BaCd₁₁ and ThMn₁₂ and the cubic or tetragonal NaZn₁₃ structure-type are located in fairly well-defined domains within a single structure map containing the A₂B₁₇, AB₁₁, AB₁₂ and AB₁₃ stoichiometries, thereby suggesting alloying additions to stabilize iron-rich alloys with uniaxial structure-types. The domains of stability of ternary structure-types of transition metal-rare earth borides are displayed within a further two structure maps. The microscopic origin of the structural stability and intrinsic magnetic behaviour of transition metals and their monoborides is investigated theoretically. A simple expression for the Curie temperature is derived in terms of the magnetic moment and high field susceptibility. It accounts for the observed trends in Curie temperature of iron and cobalt alloys.