Controllable ferromagnetism in CoCl2 monolayer: Intrinsic bipolar ferromagnetic semiconductor

Abstract

Intrinsic bipolar ferromagnetic semiconductor (BFMSs) monolayer materials with the unique spin and charge properties have become an ideal choice for exploring the next generation of high-speed, low-power and non-volatile memory devices. In this work, using first-principles calculations, we predicted that the CoCl₂ monolayer is a stable out-of-plane BFMSs with a large indirect spin band gap (2.653  eV) and its perpendicular magnetocrystalline anisotropic energy (PMAE/0.333 meV per unit cell) are mainly originate from the couplings of Co-d_yz/d_z² orbitals thorough L_x in the different spin channels and the Co-d_xz/d_yz orbitals thorough L_z in the same spin channels. And after breaking the mirror symmetry, its Janus monolayer CoClBr shows a stronger ferromagnetism, a higher Curie temperature (Tc/210 K) and a novel half-semiconductor (HSCs) property. In addition, the CoCl₂ monolayer’s Tc and PMAE can be markedly improved under the compressive strain. For example, at −2% and −6% strains, Tc and PMAE can reach maximum values of 200 K and 0.436 meV, respectively. Besides, under the electronic doping, its Tc can also be enhanced and there will be a transition from BFMS to half-metal and then to metal. These findings indicate that our work offers a candidate material for spintronics devices.