Signatures of a magnetic superstructure phase induced by ultrahigh magnetic fields in a breathing pyrochlore antiferromagnet

TL;DR

This study reveals a magnetic superstructure phase in a breathing pyrochlore antiferromagnet induced by ultrahigh magnetic fields, highlighting complex spin-lattice interactions and novel magnetic states.

Contribution

It reports the discovery of a magnetic superstructure phase in a breathing pyrochlore antiferromagnet under ultrahigh magnetic fields, supported by magnetization, magnetostriction, and magnetoelastic theory.

Findings

Identification of a two-step magnetostructural transition before the half-magnetization plateau

Observation of a three-dimensional periodic magnetic superstructure with specific spin arrangements

Linking the superstructure emergence to strong spin-lattice coupling and breathing anisotropy

Abstract

The mutual coupling of spin and lattice degrees of freedom is ubiquitous in magnetic materials and potentially creates exotic magnetic states in response to the external magnetic field. Particularly, geometrically frustrated magnets serve as a fertile playground for realizing magnetic superstructure phases. Here, we observe an unconventional two-step magnetostructural transition prior to a half-magnetization plateau in a breathing pyrochlore chromium spinel by means of state-of-the-art magnetization and magnetostriction measurements in ultrahigh magnetic fields available up to 600 T. Considering a microscopic magnetoelastic theory, the intermediate-field phase can be assigned to a magnetic superstructure with a three-dimensional periodic array of 3-up-1-down and canted 2-up-2-down spin molecules. We attribute the emergence of the magnetic superstructure to a unique combination of the strong spin-lattice coupling and large breathing anisotropy.