Strain induced metal-semiconductor transition in two-dimensional topological half metals

Spintronic applications of two-dimensional (2D) magnetic half metals and semiconductors are thought to be very promising. Here, we suggest a family of stable 2D materials [Formula: see text] [Formula: see text] (X = Cl, Br, and I). The monolayer [Formula: see text] [Formula: see text] exhibits an in-plane ferromagnetic (FM) ground state with a Curie temperature of 118 K, which is unveiled to be a 2D Weyl half semimetal with two Weyl points of opposite chirality connected by a remarkable Fermi arc. In addition, it appears that a biaxial tensile strain can lead to a metal-semiconductor phase transition as a result of the increased anomalous Jahn-Teller distortions, which raise the degeneracy of the [Formula: see text] energy level and cause a significant energy splitting. A 10% biaxial tensile strain also increases the Curie temperature to about 159 K, which originates from the enhanced Mn-Cl-Mn FM superexchange. Moreover, the metal-semiconductor transition can also be induced by a uniaxial strain. Our findings provide an idea to create 2D magnetic semiconductors through metal-semiconductor transition in half metals.