Controllable ferromagnetism in CoCl2 monolayer: Intrinsic bipolar ferromagnetic semiconductor

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.