Spin dynamics slowdown near the antiferromagnetic critical point in atomically thin FePS3

TL;DR

This study investigates how spin dynamics slow down near the antiferromagnetic critical point in atomically-thin FePS3, revealing layer-dependent critical behavior and interactions with phonons using ultrafast spectroscopy.

Contribution

It provides new insights into the layer-dependent critical slowing down of spin dynamics in 2D antiferromagnetic materials.

Findings

Demagnetization time diverges near Néel temperature

Power-law dependence of divergence with reduced temperature

Layer thickness affects critical exponent

Abstract

Two-dimensional (2D) magnetic materials have attracted much recent interest with unique properties emerging at the few-layer limit. Beyond the reported impacts on the static magnetic properties, the effects of reducing the dimensionality on the magnetization dynamics are also of fundamental interest and importance for 2D device development. In this report, we investigate the spin dynamics in atomically-thin antiferromagnetic FePS3 of varying layer numbers using ultrafast pump-probe spectroscopy. Following the absorption of an optical pump pulse, the time evolution of the antiferromagnetic order parameter is probed by magnetic linear birefringence. We observe a strong divergence in the demagnetization time near the N\'eel temperature. The divergence can be characterized by a power-law dependence on the reduced temperature, with an exponent decreasing with sample thickness. We compare our results to expectations from critical slowing down and a two-temperature model involving spins and phonons, and discuss the possible relevance of spin-substrate phonon interactions.