Qian Li, Mengmeng Yang, Cheng Gong, Rajesh V. Chopdekar, Alpha T. N’Diaye, John Turner, Gong Chen, Andreas Scholl, Padraic Shafer, Elke Arenholz, Andreas K. Schmid, Sheng Wang, Kai Liu, Nan Gao, Alemayehu S. Admasu, Sang-Wook Cheong, Chanyong Hwang, Jia Li, Feng Wang, Xiang Zhang, Ziqiang Qiu

Magnetic van der Waals (vdW) materials have emerged as promising candidates for spintronics applications especially after the recent discovery of intrinsic ferromagnetism in monolayer vdW materials. There has been a critical need for tunable ferromagnetic vdW materials beyond room temperature. Here we report a real space imaging study of itinerant ferromagnet Fe3GeTe2 and the enhancement of its Curie temperature well above ambient temperature. We find that the magnetic long-range order in Fe3GeTe2 is characterized by an unconventional out-of-plane stripe domain phase. In Fe3GeTe2 microstructures patterned by focused ion beam, the out-of-plane stripe domain phase undergoes a surprising transition at 230 K to an in-plane vortex phase that persists beyond room temperature. The discovery of tunable ferromagnetism in Fe3GeTe2 materials opens up vast opportunities for utilizing vdW magnets in room temperature spintronics devices.