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 widelyused permanent magnets are based on rare-earth elements, whose highly localized 4f 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 selfinteraction-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 (RECo5) family for RE=Y-Lu. The calculations correctly reproduce the experimentally measured trends across the series and confirm that, apart from the hypothetical compound EuCo5, SmCo5 has the strongest magnetic properties at high temperature. An orderparameter 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:1806.05646v1 [cond-mat.mtrl-sci]

First-principles calculations of the magnetocrystalline anisotropy of the prototype 2:17 cell boundary phaseYCo1-x-yFePatrick1, Matsumoto2, Staunton3 2019Journal of Magnetism and Magnetic MaterialsSelf Cite132181View full textAdd to dashboardCite

“…Previous computational studies on YCo 5 found the LSDA to yield values of both the orbital magnetic moments and the magnetocrystalline anisotropy which are smaller than measured experimentally, but including an orbital polarization correction (OPC) [56] on the TM-d orbitals corrects this discrepancy [30][31][32]. Although the relativistic DFT-DLM calculations do allow an OPC to be included [29,57,58], in the current work we do not do so due to the large number of (Fe,Cu) compositions considered. Therefore our calculated anisotropy energies are underestimates compared to experiment.…”

“…On the theoretical side, the obvious next step is to study the RE contribution to the anisotropy in Sm(Co 1−x−y Fe x Cu y ) 5 . In this case it will be essential to properly account for the crystal field effects in the calculations [77] and analyse the effects of hybridization of the 4f states with their environment [29,36]. It will be interesting to see whether addition of a small quantity of Fe or Cu boosts the anisotropy like in YCo 5 , or whether K decreases for all compositions.…”

Temperature-dependent magnetocrystalline anisotropy of rare earth/transition metal permanent magnets from first principles: The light RCo5 (R=Y, La-Gd) intermetallics

“…In summary, we have demonstrated a framework to calculate the finite-temperature MCA of RE-TM magnets. Combined with the previously established DFT-DLM method which provides finite-temperature magnetization and T C [24], we have a full framework to calculate the intrinsic properties of RE-TM magnets which requires no experimental input beyond the crystal struc-ture. The validation of our method on the RECo 5 magnet class opens the door to tackling other RE-TM magnets, like Nd-Fe-B, REFe 12 and Sm 2 Co 17 .…”

Caloric effects around phase transitions in magnetic materials described by ab initio theory: The electronic glue and fluctuating local moments

“…Their interactions with each other depend on the type and extent of the long-range magnetic order through the associated spin-polarized electronic structure 6 which itself adapts to the extent of mag-netic order. For materials with rare earth lanthanide (RE) components the strongly correlated 4f electrons are treated with our self interaction correction (SIC) approach which is parameter free and incorporates Hund's rules naturally 13 . The crucial RE contribution to the magnetic anisotropy is accounted for using crystal field theory, calculating the crystal field coefficients within DFT using a robust numerical method 14 .…”