Field-tunable toroidal moment in a chiral-lattice magnet

TL;DR

This paper reports the discovery and control of a vortex-like toroidal magnetic order in a chiral magnet, with transitions driven by magnetic fields, advancing potential spintronics applications.

Contribution

It introduces a ferritoroidal state in BaCoSiO4 and explains its formation through a first-principles Hamiltonian considering frustration and Dzyaloshinskii-Moriya interactions.

Findings

Observation of multi-stair toroidal transitions under magnetic field

Identification of a ferritoroidal vortex-like spin configuration

Theoretical explanation via microscopic Hamiltonian

Abstract

A toroidal dipole moment appears independent of the electric and magnetic dipole moment in the multipole expansion of electrodynamics. It arises naturally from vortex-like arrangements of spins. Observing and controlling spontaneous long-range orders of toroidal moments are highly promising for spintronics but remain challenging. Here we demonstrate that a vortex-like spin configuration with a staggered arrangement of toroidal moments, a ferritoroidal state, is realized in a chiral triangular-lattice magnet BaCoSiO4. Upon applying a magnetic field, we observe multi-stair toroidal transitions correlating directly with metamagnetic transitions. We establish a first-principles microscopic Hamiltonian that explains both the formation of toroidal states and the metamagnetic toroidal transition as a combined effect of the magnetic frustration and the Dzyaloshinskii-Moriya interactions allowed by the crystallographic chirality in BaCoSiO4.