Rare-earth/transition-metal magnets at finite temperature: Self-interaction-corrected relativistic density functional theory in the disordered local moment picture

Abstract

Atomic-scale computational modeling of technologically relevant permanent magnetic materials faces two key challenges. First, a material's magnetic properties depend sensitively on temperature, so the calculations must account for thermally induced magnetic disorder. Second, the most widely-used permanent magnets are based on rare-earth elements, whose highly localized 4$f$ electrons are poorly described by standard electronic structure methods. Here, we take two established theories, the disordered local moment picture of thermally induced magnetic disorder and self-interaction-corrected density functional theory, and devise a computational framework to overcome these challenges. Using the new approach, we calculate magnetic moments and Curie temperatures of the rare-earth cobalt (RECo${}_5$) family for RE=Y--Lu. The calculations correctly reproduce the experimentally measured trends across the series and confirm that, apart from the hypothetical compound EuCo${}_5$, SmCo${}_5$ has the strongest magnetic properties at high temperature. An order-parameter analysis demonstrates that varying the RE has a surprisingly strong effect on the Co--Co magnetic interactions determining the Curie temperature, even when the lattice parameters are kept fixed. We propose the origin of this behavior is a small contribution to the density from $f$-character electrons located close to the Fermi level.

arXiv comment17 pages, 11 figures

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• Toward a first-principles theory of rare-earth ions in crystals
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• Caloric effects around phase transitions in magnetic materials described by ab initio theory: The electronic glue and fluctuating local moments
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• First-principles calculations of the magnetocrystalline anisotropy of the prototype 2:17 cell boundary phase Y(Co${}_{1-x-y}$Fe${}_x$Cu${}_y$)${}_5$
• Magnetic properties of Nd6Fe13Cu single crystals
• Anisotropy at twin interfaces in $R{T}_{12}$ ($R$=rare earth, $T$=transition metal) magnets
• Magnetic moment orientation and in depth distribution of dysprosium near the surface of DyCo${}_{4.6}$ thin films determined by the analysis of their X ray circularly polarized absorption Dy $M_5$ spectra
• Magnetic properties in the metallic magnets with large anisotropy