Magnetic field dependence of the nonlinear magnetic response and tricritical point in the monoaxial chiral helimagnet Cr$_{1/3}$NbS$_{2}$

TL;DR

This study investigates the nonlinear magnetic response and phase transitions in Cr$_{1/3}$NbS$_{2}$, revealing a tricritical point and complex dynamics of chiral soliton lattice evolution under varying magnetic fields and temperatures.

Contribution

It provides the first detailed analysis of the ac magnetic response across multiple harmonics and identifies the tricritical point in Cr$_{1/3}$NbS$_{2}$, advancing understanding of chiral helimagnet phase behavior.

Findings

Identification of a tricritical point above Curie temperature.

Observation of slow domain relaxation dynamics.

Asymmetric relaxation time distribution in nonlinear regime.

Abstract

We present a comprehensive study of the magnetization dynamics and phase evolution in Cr$_{1/3}$NbS$_{2}$, which realizes a chiral soliton lattice (CSL). The magnetic field dependence of the ac magnetic response is analyzed for five harmonic components, $M_{n\omega}(H)$ $(n =1-5)$, using a phase sensitive measurement over a frequency range, $f = 11 - 10,000$ Hz. At a critical field, the modulated CSL continuously evolves from a helicity-rich to a ferromagnetic domain-rich structure, where the crossover is revealed by the onset of an anomalous nonlinear magnetic response that coincides with extremely slow dynamics. The behavior is indicative of the formation of a spatially coherent array of large ferromagnetic domains which relax on macroscopic time-scales. The frequency dependence of the ac magnetic loss displays an asymmetric distribution of relaxation times across the highly nonlinear CSL regime, which shift to shorter time-scales with increasing temperature. We experimentally resolve the tricritical point at $T_{TCP}$ in a temperature regime above the ferromagnetic Curie temperature which separates the linear and nonlinear regimes of the CSL at the phase transition. A comprehensive phase diagram is constructed which summarized the features of the field and temperature dependence of the magnetic crossovers and phase transitions in Cr$_{1/3}$NbS$_{2}$.