Rare earth magnets - bridging the gap between electronic and atomistic models

Magnets formed by alloying rare earth elements like neodymium or samarium with transition metals like iron or cobalt are the highest performance materials in use today, thanks to their: (i) large magnetization, (ii) high Curie temperature, and (iii) large coercivity.

Property (i) means that a small amount of material can be used to generate a large magnetic field, whilst properties (ii) and (iii) mean the material does not easily lose its magnetization at elevated temperatures or in the presence of other magnetic fields. However, from a mechanical, economical and environmental point of view, these materials are far from ideal, and researchers across the spectrum of industry and academia are searching for ways to optimise the properties of current designs or find new materials with reduced rare earth content. Property (iii) (coercivity) is an intensely difficult problem to understand, because it involves multiple length scales; it is being driven by long-range magnetostatic forces, but involves the propagation of domain walls and interactions between phases which may only be nanometres thick. In this talk I will describe our efforts to connect up length scales, developing the framework to incorporate the results of first-principles density-functional theory calculations into the larger length scale techniques of atomistic spin dynamics and continuum micromagnetics. In particular I will present our recent work in understanding the effect of point defects on the magnetic anisotropy of the rare earth atoms [1]. If time allows, I will also present a perspective on the interplay of magnetism and structure, taking the rare earth-free magnet MnBi and the decidedly non rare earth-free magnet Terfenol-D as key examples [2,3].

[1] C. E. Patrick, Y. Huang, L. H. Lewis and J. B. Staunton, Phys. Rev. Lett. 132, 056703 (2024)

[2] C. E. Patrick, Phys. Rev. B 106, 014425 (2022)

[3] C. E. Patrick, G. A. Marchant and J. B. Staunton, Phys. Rev. Applied 14, 014091 (2020)

Bio: Chris Patrick is a Departmental Lecturer and Senior Research Fellow in the Department of Materials at the University of Oxford. After obtaining a DPhil in that department, he carried out postdoctoral work at the Technical University of Denmark and at the University of Warwick, before returning to Oxford in 2019.