Multi-ion crystal field analysis: Methodology and application to (ErxPr1−x)2Fe14B (invited)

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Abstract
The advent of Nd2Fe14B has spawned considerable interest in multi‐ion crystal field calculations, since it is the rare‐earth crystal field interaction which, in the main, gives rise to the high magnetocrystalline anisotropy necessary for a permanent magnet material. To properly analyze this system, multi‐ion calculations are required, due to the fact that the rare‐earth ions occupy two crystallographically inequivalent sites, each of which is fourfold degenerate. In the first part of this paper, we describe a procedure for performing multi‐ion crystal field calculations which is based on the use of space group transformation matrices to generate both the positions and local axes of the crystallographically equivalent ions. The principal advantage of this method is that all symmetry information can be imported from data files, rather than being coded into the computer program, allowing for a program which is completely structure independent. Another advantage is the ease with which mixed rare‐earth systems [such as (ErxPr1−x)2Fe14B ] can be analyzed. In the second part of the paper, we present results obtained by the above described method for the system (ErxPr1−x)2Fe14B, including predictions of both the low‐temperature magnetic structure and the magnetic phase diagram.