Emerging intrinsic magnetism in two-dimensional materials: theory and applications

Abstract

The intrinsic magnetism has long been pursued in two-dimensional (2D) materials down to one-atomic layer thickness. But only very recently, the intrinsic magnetism of monolayer CrI3, Fe3GeTe2, FePS3, VSe2 and bilayer Cr2Ge2Te6 are verified in experiment by optical measurement, Raman spectrum and conventional magnetism measurement. Among them, the intralayer exchange interaction of FePS3 is antiferromagnetic while all the others are ferromagnetic. Most of the ferromagnetic orders in these materials are induce by super exchange interaction. Monolayer Fe3GeTe2 and VSe2 exhibit metallic character while all the others are semiconductor or insulator. Stable spontaneous magnetization can exist in these monolayer 2D materials because of their strong anisotropy. The anisotropy is mostly from the strong spin–orbit coupling of heavy atoms (CrI3, Cr2Ge2Te6, Fe3GeTe2). Asymmetric lattice distortion (FePS3) or the increased density of state near Fermi level (VSe2) may also contribute to the anisotropy. The relationship between anisotropy and stable spontaneous magnetization are discussed based on spin wave theory and Mermin-Wagner theorem. About the application, spintronics may be the most direct benefitted field. Considering the relationship between conductance and magnetic structure, the applications related with the transport property are also widely investigated. Similarly, as the coupling between spin, phonon and photon are prominent in these magnetic 2D materials, the applications based on the magnetocaloric effect and magneto-optic effect are promising. And these magnetic 2D materials may be also applied as catalyst in water-splitting or electrode of supercapacitor.