This paper demonstrates a higher-temperature surface and lower-temperature bulk phase transition in CrSBr, a van der Waals layered antiferromagnet. Using electric dipole and quadrupole second harmonic generation (SHG), the researchers resolve surface and bulk magnetism, revealing a counterintuitive enhancement of surface magnetism. Density functional theory calculations attribute this to the suppression of ferromagnetic-antiferromagnetic competition at the surface, offering viable pathways to enhance magnetism in 2D materials.

Xiaoyu Guo, Wenhao Liu, Jonathan Schwartz, Suk Hyun Sung, Dechen Zhang, Makoto Shimizu, Aswin L. N. Kondusamy, Lu Li, Kai Sun, Hui Deng, Harald O. Jeschke, Igor I. Mazin, Robert Hovden, Bing Lv, Liuyan Zhao