Air-Stable and Layer-Dependent Ferromagnetism in Atomically Thin van der Waals CrPS<sub>4</sub>
Joolee Son, Suhan Son, Pyeongjae Park, Maengsuk Kim, Zui Tao, Juhyun Oh, Taehyeon Lee, Sanghyun Lee, Junghyun Kim, Kaixuan Zhang, Kwanghee Cho, Takashi Kamiyama, Jun Hee Lee, Jun Hee Lee, Kin Fai Mak, Jie Shan, Miyoung Kim, Je‐Geun Park, Jieun Lee, Jieun Lee
Abstract
Ferromagnetism in two-dimensional materials presents a promising platform for the development of ultrathin spintronic devices with advanced functionalities. Recently discovered ferromagnetic van der Waals crystals such as CrI3, readily isolated two-dimensional crystals, are highly tunable through external fields or structural modifications. However, there remains a challenge because of material instability under air exposure. Here, we report the observation of an air-stable and layer-dependent ferromagnetic (FM) van der Waals crystal, CrPS4, using magneto-optic Kerr effect microscopy. In contrast to the antiferromagnetic (AFM) bulk, the FM out-of-plane spin orientation is found in the monolayer crystal. Furthermore, alternating AFM and FM properties observed in even and odd layers suggest robust antiferromagnetic exchange interactions between layers. The observed ferromagnetism in these crystals remains resilient even after the air exposure of about a day, providing possibilities for the practical applications of van der Waals spintronics.