Tuning $L1_0$ Order and Magnetocrystalline Anisotropy in Rare-Earth-Free Transition Metal Magnets: an Integrated, First Principles Approach
Date:
Contributed talk at the Joint European Magnetic Symposia 2023.
Abstract
We report results from an holistic approach for modelling both atomic ordering and the subsequent magnetocrystalline anisotropy energy (MAE) of magnetic materials with application to the design of novel, rare-earth-free permanent magnets. This computationally efficient technique allows for fast exploration of the materials design space and could open up a new route for materials discovery. In the present work, we study the class of magnetic materials which chemically order into the L10 structure. It is known that such materials often have large MAE values, with prime examples being FePt and CoPt. However, materials such as these use component elements which have a high criticality. Ab initio theory has previously confirmed that it is the tetragonal, L10 order that produces the high MAE values measured in these materials[1]. There is therefore a desire to discover new L10 materials which are made using more abundant elements, but which still retain desirable magnetic properties. One such candidate material is L10-FeNi, found in meteoritic, tetrataenite samples. This material is known to have a high uniaxial anisotropy, but a low chemical ordering temperature and sluggish kinetics make it challenging to manufacture in a laboratory setting. Here, we consider introducing a third element into the Fe-Ni system at a low concentration to promote ordering tendencies and enhance its predicted MAE, studying systems with the general formula Fe50-xNi50-yXx+y for a variety of additives, examples including X=Pd, Co, Pt, Al. Crucially, our modelling enables us to predict the nature of any chemical order[2] and then go on to predict the MAE for a given system[1], using the same ab initio formalism for both aspects of the modelling approach. The ordering behaviour predicted on adding these dopants is rich and a variety of chemical orderings are obtained. Interestingly, we find that it is often the addition of light elements such as Al which enhance the MAE the most. We are also able to study the impact of magnetic order on predicted atomic order and show that annealing samples in an applied magnetic field may enhance chemical ordering temperatures by altering the magnetic state of a material[3].
Acknowledgements
We gratefully acknowledge the support of the UK EPSRC, Grant No. EP/W021331/1. This work was also supported by the U.S. Department of Energy, Office of Basic Energy Sciences under Award Number DE SC0022168 and by the U.S. National Science Foundation under Award ID 2118164.
References
[1] J.B. Staunton et al., Phys. Rev. B 74, 144411 (2006)
[2] C. D. Woodgate and J. B. Staunton, Phys. Rev. B 105, 115124 (2022).
[3] C. D. Woodgate D. Hedlund, L. H. Lewis, J. B. Staunton, arXiv:2303.00641 (2023)