Mind the Gap: The Case for Developing L10 FeNi (Tetrataenite) as a ‘Hard’ Permanent Magnet
Date:
Invited talk at the Power Electronics, Machines and Drives (PEMD) 13th International Conference, organised by the IET.
Abstract
L10 FeNi (the meteoritic mineral tetrataenite) is a ferromagnetic, atomically ordered material comprising alternating layers of Fe and Ni atoms in a tetragonal crystal structure. Consisting entirely of two earth-abundant elements, and with experimental reports of a large saturation magnetistaion and impressive magnetocrystalline anisotropy, it is under scrutiny as a sustainable permanent magnet for advanced applications.
However, at present there remain two fundamental questions to address regarding development of this material. The first relates to the L10 atomic disorder-order transition temperature—the temperature below which, given suitable processing, the atoms in the material will arrange themselves into this crucial tetragonal crystal structure. The second relates to the value of its magnetocrystalline anisotropy energy, defining how ‘hard’ a permanent magnet the atomically ordered phase might be. Despite a number of theoretical and experimental studies on this system, there is no clear consensus in the literature on an exact value for either of these two key quantities.
In this talk I will elucidate both of these aspects using a holistic modelling approach based on density functional theory calculations of the material’s electronic structure. Crucially, the modelling approach uses the same description of the underlying electronic ‘glue’ of the material to describe both atomic ordering and magnetocrystalline anisotropy. I will present results showing how an applied magnetic field and/or mechanical strain during the annealing process can affect the atomic disorder-order transition, and also discuss the origins of the wide spread in reported values for the material’s experimentally reported uniaxial anisotropy energy. These results provide fundamental physical insight into this technologically relevant magnetic material.