Structural disorder versus chiral magnetism in Cr$_{1/3}$NbS$_2$

TL;DR

This study investigates the disordered crystal structure of Cr$_{1/3}$NbS$_2$, revealing how occupational disorder affects its magnetic properties and challenges previous assumptions of its helicoidal spin structure.

Contribution

The paper provides a detailed characterization of the disordered structure of Cr$_{1/3}$NbS$_2$ and demonstrates its impact on magnetic ordering, contrasting with prior structural models.

Findings

Disordered Cr sub-lattice reduces magnetic ordering temperature from 130 K to 88 K.

Correlated disorder modifies the field dependence of magnetization.

The compound exhibits ferromagnetic order with in-plane anisotropy, contrary to previous helicoidal assumptions.

Abstract

The crystal structure of a disordered form of Cr$_{1/3}$NbS$_2$ has been characterized using diffraction and inelastic scattering of synchrotron radiation. In contrast to the previously reported symmetry (P6$_3$22), the crystal can be described by a regular twinning of an average P6$_3$ structure with three disordered positions of the Cr ions. Short-range correlations of the occupational disorder result in a quite intense and structured diffuse scattering; a static nature of the disorder was unambiguously attributed by the inelastic x-ray scattering. The diffuse scattering has been modeled using a reverse Monte-Carlo algorithm assuming a disorder of the Cr sub-lattice only. The observed correlated disorder of the Cr sub-lattice reduces the temperature of the magnetic ordering from 130 K to 88 K and drastically modifies the field dependence of the magnetization as it is evidenced by the SQUID magnetometery. We conclude, that in contrast to the helicoidal spin structure assumed for P6$_3$22 form, the compound under study is ferromagnetically ordered with a pronounced in-plane anisotropy.