Phase Engineering of Two-Dimensional Spinel-Type Manganese Oxides.

Two-dimensional (2D) magnetic materials have been of interest due to their unique long-range magnetic ordering in the low-dimensional regime and potential applications in spintronics. Currently, most of the studies are focused on strippable van der Waals magnetic materials with layered structures, which typically suffer from a poor stability and scarce species. Spinel oxides have a good environmental stability and rich magnetic properties. However, the isotropic bonding and close-packed nonlayered crystal structure make their 2D growth challenging, let alone the phase engineering. Herein, we report a phase-controllable synthesis of 2D single-crystalline spinel-type oxides for the first time. Using the van der Waals epitaxy strategy, the thicknesses of the obtained tetragonal and hexagonal manganese oxide (Mn 3 O 4 ) nanosheets can be tuned down to 7.1 nm and one unit cell (0.7 nm), respectively. The magnetic properties of these two phases are evaluated using vibrating-sample magnetometry and first-principle calculations. Both structures exhibit a Curie temperature of 48 K. Owing to its ultrathin geometry, the Mn 3 O 4 nanosheet exhibits a superior ultraviolet detection performance with an ultralow noise power density of 0.126 pA/Hz 1/2 . This study broadens the range of 2D magnetic semiconductors and highlights their potential applications in future information devices. This article is protected by copyright. All rights reserved.