A family of high-temperature ferromagnetic semiconducting monolayers: spin-dependent carrier mobility anisotropy and elliptic dichroism

Two dimensional magnets have received increasing attentions since Cr2Ge2Te6 and CrI3 were experimentally exfoliated and measured in 2017. Although layered ferromagnetic metals were demonstrated at room temperature, a layered ferromagnetic semiconductor with high Curie temperature (Tc) is yet to be unveiled. Here, we theoretically predicted a family of high Tc ferromagnetic monolayers, namely CrCX (C=S, Se and Te; X=Cl, Br and I). Their Tc values were predicted up to over 500 K with Monte Carlo simulations. At least six members among them show semiconducting bandgaps varying from less than 1 eV to over 2 eV. These semiconductor monolayers also show extremely large anisotropy, i.e. ~102 for effective masses and ~103 for carrier mobilities, along the two lattice directions of these layers. Such anisotropy of electronic structures leads to strong elliptic dichroism, in different from previously known circular and linear dichroisms in layered materials, which is a result of coupled spin freedom and wavefunction symmetry. These results manifest the potential of this 2D family for both fundamental research and high performance spin-dependent electronic and optoelectronic devices.