Extended exchange interactions stabilize long-period magnetic structures in Cr$_{1/3}$NbS$_2$

TL;DR

This study uses inelastic neutron scattering to measure the spin wave spectrum of Cr$_{1/3}$NbS$_2$, revealing that extended exchange interactions up to third nearest neighbors stabilize its long-period magnetic structures, including the chiral soliton lattice.

Contribution

It provides a detailed microscopic understanding of the exchange interactions in Cr$_{1/3}$NbS$_2$, highlighting the role of extended interactions in stabilizing complex magnetic states.

Findings

Exchange constants up to third nearest neighbors were determined.

Both second and third nearest neighbor interactions are crucial for magnetic structure stability.

The Heisenberg model with anisotropy explains the observed spin wave spectrum.

Abstract

The topologically-protected, chiral soliton lattice is a unique state of matter offering intriguing functionality and it may serve as a robust platform for storing and transporting information in future spintronics devices. While the monoaxial chiral magnet Cr$_{1/3}$NbS$_2$ is known to host this exotic state in an applied magnetic field, its detailed microscopic origin has remained a matter of debate. Here we work towards addressing this open question by measuring the spin wave spectrum of Cr$_{1/3}$NbS$_2$ over the entire Brillouin zone with inelastic neutron scattering. The well-defined spin wave modes allow us to determine the values of several microscopic interactions for this system. The experimental data is well-explained by a Heisenberg Hamiltonian with exchange constants up to third nearest neighbor and an easy plane magnetocrystalline anisotropy term. Our work shows that both the second and third nearest neighbor exchange interactions contribute to the formation of the helimagnetic and chiral soliton lattice states in this robust three-dimensional magnet.