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Séminaire Matériaux

Institut Néel

Mardi 6 juillet 2021 à 9h30

Lien zoom : https://univ-grenoble-alpes-fr.zoom.us/j/94585938426?pwd=clMxMFlUVDd1Q0g3RXNuQWN0NTBsdz09

Titre : Tunable toroidal order and spin chirality in a triangular lattice magnet: the role of chirality

Résumé : 

Toroidal moments naturally arise from vortex-like arrangements of spins. A spontaneous arrangement of toroidal moments, coined ferrotoroidal order, has recently been found in a few linear magnetoelectric materials. However, tuning toroidal moments in these materials is challenging due to the requirement of a conjugate toroidal field. A simple equilateral triangle with spin vortices breaking both the spatial inversion and time reversal symmetry is envisaged to yield positive or negative toroidal moments. When the motif is chiral (scalar spin chirality), manipulating toroidal moments directly by a magnetic field becomes possible. The outstanding question is how to materialize these states in a real material. In this talk, I present the realization of readily switching between ferritoroidal and ferrotoroidal phases by a small magnetic field, in a chiral triangular-lattice magnet BaCoSiO4 with such tri-spin vortices. Accompanying with the toroidal transition, the scalar spin chirality also undergoes a ferri-ferroic transition. I will discuss the underpinning physical picture of this novel transition and attribute it to a combined result of an unusual hierarchy of frustrated exchange couplings and antisymmetric exchange interactions driven by the crystallographic chirality. These findings open up new avenues for realizing easily tunable toroidal orders and spin chirality.