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Quantum Theory of Materials seminar, PGI-1/IAS-1

Dr. Eduardo Mendive-Tapia

Ab-initio theory of pair- and multi-local moment interactions: The magnetism of Mn3A from fluctuating local moments

12 Sep 2018 11:30
PGI Lecture Hall

University of Warwick, UK


In order to describe magnetic order in metals it is essential to carefully account for the itinerant electrons. These itinerant electrons form a spin-polarized 'glue' which binds together the nuclei and can lead to the emergence of local magnetic moments. This glue is complicated and might qualitatively change when it adapts to the type and extent of magnetic order. Crucially, it determines the motion of the local moments and mediates the interactions between them. Given the complexity of the glue it is therefore unsurprising that in metallic materials the interactions between local moments must be described not only by simple pairwise terms, but also with terms describing multi-site magnetic interactions. Here, we present a Disordered Local Moment (DLM) theory to calculate both pairwise and multi-local moment interactions via modelling the local moment thermal fluctuations and using magnetically constrained Density Functional Theory (DFT) calculations. The theory describes first- and second-order magnetic phase transitions and provides the material's free energy and magnetic ordering as functions of temperature, magnetic field, lattice parameters and atomic positions.

The theory is applied to study the geometrically frustrated magnetism of Mn3A in all its hexagonal, cubic and tetragonal structures. The results are in excellent agreement with experiment. For example, we predict the stabilization of both triangular antiferromagnetic (AFM) and ferrimagnetic phases with right transition temperatures. We also reproduce the pressure-temperature experimental phase diagram of Mn3Pt, adequately describing the AFM-AFM transition, consequent tricritical points and potential for barocaloric applications.


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