Probing Short-Range Correlations in the van der Waals Magnet CrSBr by Small-Angle Neutron Scattering

TL;DR

This study uses Small-Angle Neutron Scattering to reveal short-range magnetic correlations in CrSBr, showing their development above the long-range ordering temperature and intrinsic nature in the monolayer limit.

Contribution

It provides the first direct observation of short-range magnetic correlations in CrSBr and demonstrates the effectiveness of SANS in studying van der Waals magnets.

Findings

Short-range correlations reach ~3 nm at TN

Correlations develop below 200 K, above TN

No evidence of frustrated phases within 2-200 nm range

Abstract

The layered metamagnet CrSBr offers a rich interplay between magnetic, optical and electrical properties that can be extended down to the two-dimensional (2D) limit. Despite the extensive research regarding the long-range magnetic order in magnetic van der Waals materials, short-range correlations have been loosely investigated. By using Small-Angle Neutron Scattering (SANS) we show the formation of short-range magnetic regions in CrSBr with correlation lengths that increase upon cooling up to ca. 3 nm at the antiferromagnetic ordering temperature (TN ~ 140 K). Interestingly, these ferromagnetic correlations start developing below 200 K, i.e., well above TN. Below TN, these correlations rapidly decrease and are negligible at low-temperatures. The experimental results are well-reproduced by an effective spin Hamiltonian, which pinpoints that the short-range correlations in CrSBr are intrinsic to the monolayer limit, and discard the appearance of any frustrated phase in CrSBr at low-temperatures within our experimental window between 2 and 200 nm. Overall, our results are compatible with a spin freezing scenario of the magnetic fluctuations in CrSBr and highlight SANS as a powerful technique for characterizing the rich physical phenomenology beyond the long-range order paradigm offered by van der Waals magnets.