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PGI-1 Talk: Dr. Eduardo Mendive-Tapia

Ab-initio origin of the short-period magnetism of MnGe from thermally fluctuating local moments

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08 Jul 2020 11:30
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MPI Düsseldorf, Germany

Abstract:

Magnetic B20-type compounds, such as MnSi and FeGe, host helimagnetic and skyrmion phases which are canonically explained through the combination of strong ferromagnetic isotropic exchange with weaker chiral Dzyaloshinskii-Moriya interactions (DMI).

MnGe seems to evade this paradigm since it shows a non-collinear triple-q phase whose period is so small that it cannot be explained in terms of the DMI. Here it will be demonstrated that the central aspects of MnGe's magnetism, including its characteristic short length-scale and volume-dependent magnetic properties, stem out directly from isotropic magnetic interactions with competing signs. This will be shown by means of a first-principles description for the thermal fluctuations of the Mn local moments, from which pairwise interactions are obtained in the paramagnetic state such that their effect is isolated from higher order interactions to generally describe the most stable potential magnetic phases at high-temperature.

The theory presented provides the first-principles Gibbs free energy of the magnetic system, which here is amenable to systematic improvement by considering higher-order interactions. The presence of the latter is used to show how to describe a triple-q magnetic phase that is the most stable state in the temperature-magnetic field phase diagram of MnGe. The robustness of the approach presented is supported by applying the theory to FeGe, where the canonical helimagnetic B20 picture is quantitatively recovered.

Contact

Dr. Manuel dos Santos Dias
Phone: +49 2461 61-5956
Fax: +49 2461 61-2850
email: m.dos.santos.dias@fz-juelich.de