Magnetic Superexchange Induced Quantum Phase Transition in Cr₂B₂ MBene

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 Cr 2 B 2 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 Cr 2 B 2 O 2, 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 Cr 2 B 2 MBene and offer a new avenue to obtain magnetic multifunctional materials for spintronic devices.