New theory of defect-induced crystal field perturbations in rare-earth magnets - Editors' suggestion for PRL, Jan. 2024
Chris Patrick and colleagues have published an article in Physical Review Letters which has been highlighted by the editors as an Editors' Suggestion.
"Theory of defect-induced crystal field perturbations in rare-earth magnets" by Christopher E. Patrick, Yixuan Huang, Laura H. Lewis, and Julie B. Staunton, Phys. Rev. Lett. 132, 056703 (2024), https://doi.org/10.1103/PhysRevLett.132.056703
The article presents a first-principles method which quantifies the effect of defects on macroscopic properties so that the magnetic anisotropy energy of rare-earth systems is accurately described.
Pretamag computational modelling uncovers the crucial role of Fe in determining the hard magnetic properties of the ubiquitous magnet Nd2Fe14B
Nd2Fe14B's unsurpassed, hard magnetic properties for a wide range of temperatures result from a combination of a large volume magnetization from Fe and a strong single-ion anisotropy from Nd. Here, using finite temperature first-principles calculations, we focus on the other crucial roles played by the Fe atoms in maintaining the magnetic order on the Nd sublattices, and hence the large magnetic anisotropy, and directly generating significant uniaxial anisotropy at high temperatures. We identify effective spins for atomistic modeling from the material's interacting electrons and quantify pairwise and higher order, nonpairwise magnetic interactions among them. We find the Nd spins couple most strongly to spins on sites belonging to two specific Fe sublattices: 8j1 and 8j2. Moreover, the Fe 8j1 sublattice also provides the electronic origin of the unusual, nonmonotonic temperature dependence of the anisotropy of Y2Fe14B. Our work provides atomic-level resolution of the properties of this fascinating magnetic material.
For full details please see the article by Juba Bouaziz, Chris Patrick and Julie Staunton published as a letter in Physical Review B (107, L020401, (2023)) and
George Marchant to be awarded a PhD for his work on the theory of magnetostriction
George’s PhD work fitted into part of the “Pretamag” project. George investigated the phenomenon of magnetostriction which is the change of shape that can occur when a magnetic material is placed in a magnetic field. It has many applications in sensor devices and there is a need for a deeper fundamental understanding at a microscopic level for future device design.
George achieved some excellent results which describe very clearly the hitherto unexplained way in which the magnetostriction of iron changes when it is heated up and also what happens when iron is alloyed with other elements https://doi.org/10.1103/PhysRevB.99.054415. With Chris Patrick and Julie Staunton, he also completed work on some rare earth - iron magnets that show some of the best magnetostrictive properties which will also shortly be reported in the scientific literature (Physical Review Applied). George's thesis sets out the context, describes his original findings and assesses the next steps for the field. He submitted the thesis for the degree of Doctor of Philosophy in April this year and in June underwent a viva examination with 2 academic examiners who recommended that he be awarded the degree.