Magnetic Superexchange Induced Quantum Phase Transition in Cr₂B₂ MBene

Abstract

Stable long-range magnetic order in low-dimensional semiconductors up to room temperature has long been the pursuit of researchers for their potential applications in the field of spintronic and memory devices. However it is a great challenge to achieve magnetic phase transition together with a controllable band structure in two-dimensional magnetic materials simultaneously. Through fully terminated oxygen group adsorption, the transformation from ferromagnetic metal to antiferromagnetic semiconductor with a high Néel temperature (425 K) has been achieved in Cr2B2 MBene, which is attributed to superexchange interaction between the interlayer magnetic chromium (Cr) atoms. Furthermore, exotic quantum phase transition between two different antiferromagnetic states of Cr2B2O2, together with the transition from semiconductor to metal, is observed when applying compressive strain. Interestingly, ferromagnetic half-metal and ferromagnetic semiconductor states are achieved by nonuniform oxygen group adsorption, resulting from electrical potential difference between the Cr atomic layers and thus built-in electric field. Our results reveal the origin of magnetic phase transition in Cr2B2 MBene and offer a new avenue to obtain magnetic multifunctional materials for spintronic devices.