Magnetic order in XY-type antiferromagnetic monolayer CoPS3 revealed by Raman spectroscopy

Mermin-Wagner-Coleman theorem predicts no long-range magnetic order at finite temperature in the two-dimensional (2D) isotropic systems, but it does predict a quasi-long-range order with a divergent correlation length at the Kosterlitz-Thouless (KT) transition for planar magnets. As a representative of two-dimensional planar antiferromagnets, single-layer CoPS3 carries the promise of monolayer antiferromagnetic platforms for the ultimately thin spintronics. Here, with the aid of magnetostriction which is sensitive to the local magnetic order, we observe the signature phonon mode splitting of below T-KT in monolayer CoPS3. The two-magnon signal in the monolayer one manifests the associated magnetic transition. It indicates the quasi-long-range order in an exact 2D planar spin model below KT phase transition. The ratio (J'/J) between the interlayer and intralayer interactions, which characterizes the 2D behaviors, is evaluated to be around 0.03. Our results provide an efficient method to detect the quasi-long-range antiferromagnetic ordering in the two-dimensional magnets down to the monolayer limit.

Automated summary

The Mermin-Wagner-Coleman theorem predicts the absence of long-range magnetic order in two-dimensional isotropic systems at finite temperature, but does predict quasi-long-range order at the Kosterlitz-Thouless transition for planar magnets. By utilizing magnetostriction sensitive to local magnetic order, phonon mode splitting and two-magnon signals were observed in monolayer CoPS3 below the KT transition temperature, indicating quasi-long-range order in an exact 2D planar spin model. The ratio of interlayer to intralayer interactions (J'/J) characterizing 2D behaviors was evaluated to be around 0.03, providing an efficient method to detect quasi-long-range antiferromagnetic ordering in two-dimensional magnets down to the monolayer limit.