Neutrons for Science and Industry

Skyrmion formation and large thermoelectric response in centrosymmetric RKKY magnets

by Dr Maximilian Hirschberger (RIKEN)

Europe/Berlin
Zoom Webinar

Zoom Webinar

https://tum-conf.zoom.us/j/96181143364?pwd=TnJ2OVFJWTZGQUZ1OVltOEFDSEpoUT09
Description
In recent years, the realization of skyrmion spin textures in the following material classes has drawn considerable attention: (1) ferromagnetic thin plates with dipolar interactions and large "bubbles" of lateral size 200-4000 nm, e.g. in manganites or in the Heusler family, (2) non-centrosymmetric bulk crystals such as the B20 compound MnSi, and (3) inversion-breaking interfaces such as SrRuO3/SrRuIr3. In the second and third cases, where skyrmions are typically 10-300 nm in diameter, Dzyaloshinskii-Moriya interactions (DMI) play a crucial role in stabilizing the non-coplanar magnetic order.
We report here on the exploration of a new paradigm, namely the realization of skyrmions in centrosymmetric bulk crystals with competing interactions, where DMI does not appear in the free energy functional. In this new family, the crystalline space group dictates the symmetry of the skyrmion lattice: While the hexagonal systems Gd2PdSi3 [1] and Gd3Ru4Al12 [2] harbor triangular lattices of spin vortices, a square skyrmion lattice was reported in tetragonal GdRu2Si2 in March 2020 [3].
We focus on the hexagonal compound Gd3Ru4Al12 [2], where we used elastic neutron scattering and resonant elastic x-ray scattering to detect the spiral ground state, as well as tiny spin-vortices (size ~2-3 nanometers) in an intermediate range of temperature and magnetic fields. We have also observed skyrmions in real-space imaging experiments. Moreover, large (thermo-)electric transport responses emerge due to the ultra-dense arrangement of magnetic vortices in this material class.
Lastly, we will speculate about the nature of the excitation spectrum on the basis of unpublished specific heat data.
 
[1] T. Kurumaji et al., Science 365, 914-918 (2019)
[2] M. Hirschberger et al., Nat. Comms. 10, 5831 (2019)
[3] N. D. Khanh et al., arXiv:2003.00626 (2020)

 

This is lecture is presented online as a Zoom Webinar.

Organized by

Dr. Christian Franz
Dr. Christian Lang