# Magnetism and Alloy Theory

### Professor JB Staunton

The main theme running through most of the ** Magnetism and Alloy Theory Group**'s research is a description of the various properties of materials via a careful account of their electronic "glue" or structure which includes spin polarisation and relativistic effects such as spin-orbit coupling. This requires HPC techniques and resources such as those available at the Centre for Scientific Computing (CSC) at the University of Warwick. The Group studies theoretical metallic magnetism in this way and also, with the same electronic basis, a theory for the types of alloys that can form when two or more metallic elements are combined. A strength of the work is that it is `first principled' so that many aspects can be tested in quantitative detail by a range of experimental measurements. The Group collaborates with several others both nationally and internationally and participates actively in the large European electronic structure PSI-K network. It is engaged in a number of different projects. These concern the development of ab-initio electronic structure theory beyond standard DFT to include the effects of strong electron correlations and finite temperatures e.g. to rare earth and transition metal material properties. There are ongoing applications to rare earth-transition metal permanent magnets, spintronics, magnetic properties of heterostructures and nanoclusters, magnetocaloric and magnetic shape memory materials and also electrocaloric materials.

Theory modelling has produced a generic phase diagram of the magnetic ordering of heavy rare earth metals.

The Group was involved in a joint experiment/theory study, B. Frandsen et al. Phys. Rev. Lett. **116**, 197204, (2016) which was featured on Science Newsline " Revealing the Nature of Magnetic Interactions in Manganese Oxide".

A paper from the Group, L. Petit et al. Phys. Rev. Lett. 115, 207201 (2015), on EPSRC-funded work on rare earth magnets carried out in collaboration with STFC Daresbury and Ames Lab. USA was featured on the front page of issue 20 of Physical Review Letters **115 **(2015).

The Group is associated with the **Collaborative Computational Project (CCP) CCP-mag.**

CCP-mag on computational multi-scale magnetism is one of many CCPs. This project brings together UK researchers with an interest in computational methods for simulations of magnetism in various systems. It embraces simulations on different length scales, starting from ab initio calculations of magnetic properties (based on the full quantum mechanical description), over atomistic modelling, representing magnetic materials by spin models, to micromagnetics, utilising finite element techniques to describe larger systems or whole devices.

**Some recent publications from the Magnetism and Alloy Theory Group:**

Cubic MnSb: Epitaxial growth of a predicted room temperature half-metal by James D. Aldous, Christopher W. Burrows, Ana M. Sánchez, Richard Beanland, Ian Maskery, Matthew K. Bradley, Manuel dos Santos Dias, Julie B. Staunton, and Gavin R. Bell Phys. Rev. B **85**, 060403(R) (2012).

'Trends in the magnetic properties of Fe, Co, and Ni clusters and monolayers on Ir(111), Pt(111), and Au(111)' by S Bornemann, O Sipr, S Mankovsky, S Polesya, J B Staunton, W Wurth, H Ebert, J Minar, Phys. Rev. B **86**, 104436, (2012).

'Atomic-scale engineering of magnetic anisotropy of nanostructures through interfaces and interlines.' by S Ouazi, S Vlaic, S Rusponi, G Moulas, P Buluschek, K Halleux, S Bornemann, S Mankovsky, J Minár, J B Staunton, H Ebert, H Brune, Nature Communications. **12/2012**; 3:1313.

'Tuning the metamagnetism of an antiferromagnetic metal' by J B Staunton, M dos Santos Dias, J Peace, Z. Gercsi, and K. G. Sandeman, Phys. Rev. B **87**, 060404(R), (2013).

'Generalized inclusion of short-range ordering effects in the coherent potential approximation for complex-unit-cell materials', by A. Marmodoro, A Ernst, S Ostanin and J B Staunton, Phys. Rev. B **87**, 125115 (2013).

'Fluctuating local moments, itinerant electrons, and the magnetocaloric effect: Compositional hypersensitivity of FeRh' by J. B. Staunton, R. Banerjee, M. dos Santos Dias, A. Deak, and L. Szunyogh, Phys. Rev. B **89**, 054427, (2014).

' Metallic magnetism at finite temperatures studied by relativistic disordered moment description: Theory and application' by A. Deak, E. Simon, L. Balogh, L. Szunyogh, M. dos Santos Dias, and J. B. Staunton, Phys. Rev. B **89, **224401, (2014).

' Improvement of magnetic hardness at finite temperatures: *Ab initio* disordered local-moment approach for YCo5' by M. Matsumoto, R. Banerjee and J. B. Staunton, Phys. Rev. B **90**, 054421, (2014).

'Using density functional theory to describe slowly varying fluctuations at finite temperatures: local magnetic moments in Gd and the 'not so local' moments of Ni' by J. B. Staunton, A. Marmodoro and A. Ernst, Journal of Physics-Condensed Matter **26, **274210, (2014).

'Complex Magnetism of Lanthanide Intermetallics and the Role of their Valence Electrons: Ab Initio Theory and Experiment' by

L. Petit, D. Paudyal, Y. Mudryk, K. A. Gschneidner, Jr., V. K. Pecharsky, M. Lüders, Z. Szotek, R. Banerjee, and J. B. Staunton, Phys. Rev. Lett. **115**, 207201 (2015).

'Statistical physics of multicomponent alloys using KKR-CPA' by Suffian N. Khan, J. B. Staunton, and G. M. Stocks, Phys. Rev. B **93**, 054206, (2016).

'Influence of structural defects on the magnetocaloric effect in the vicinity of the first order magnetic transition in Fe50.4Rh49.6' by V. I. Zverev, A. M. Saletsky, R. R. Gimaev, A. M. Tishin, T. Miyanaga, and J. B. Staunton, Applied Physics Letters **108**, 192405 (2016); doi: 10.1063/1.4949355

'Verification of Anderson superexchange in MnO via magnetic pair distribution function analysis and ab initio theory' by Benjamin A. Frandsen, Michela Brunelli, Katharine Page, Julie B. Staunton, and Simon J. L. Billinge, Phys. Rev. Lett. **116**, 197204, (2016); doi: http://dx.doi.org/10.1103/PhysRevLett.116.197204

'Temperature-dependent transport properties of FeRh' by S. Mankovsky, S. Polesya, K. Chadova, H. Ebert, J. B. Staunton, T. Gruenbaum, M. A. W. Schoen, C. H. Back, X. Z. Chen, and C. Song, Phys. Rev. B **95**, 155139, (2017). https://doi.org/10.1103/PhysRevB.95.155139

'Theory of Magnetic Ordering in the Heavy Rare Earths: Ab Initio Electronic Origin of Pair- and Four-Spin Interactions' by Eduardo Mendive-Tapia and Julie B. Staunton, Phys. Rev. Lett. **118**, 197202, (2017). https://doi.org/10.1103/PhysRevLett.118.197202