We report a comprehensive high-pressure study, up to 21.1 GPa, on the antiferromagnetic topological insulator EuSn 2 As 2 achieved through synchrotron X-ray diffraction, Raman scattering, electrical resistance, magnetic resistance, and Hall transport measurements in combination with first-principles calculations. The Néel temperatures determined from resistance are increased from (24±1) to (77±8) K under pressure, which is a result of enhanced magnetic exchange couplings between Eu 2+ ions yielded by our first-principles calculations. The negative magnetoresistance of EuSn 2 As 2 persists to higher temperatures accordingly. However, the enhancement of the observed Néel temperatures deviates from the calculations above 10.0 GPa. In addition, the magnitude of the magnetoresistance, Hall coefficients, and charge carrier densities show abrupt changes between 6.9 and 10.0 GPa. The abrupt changes likely originate from a pressure-induced valence change of Eu ions from a divalent state to a divalent and trivalent mixed state or are related to the structural transition revealed by Raman scattering measurements. Our results provide insight into magnetism variation in EuSn 2 As 2 and similar antiferromagnetic topological insulators under pressure.antiferromagnetism, topological insulator, high pressure

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Two-dimensional (2D) magnetic materials with nontrivial topological states have recently drawn considerable attention. Among them, 2D metal-organic frameworks (MOFs) are standing out due to their advantages such as the easy synthesis in practice and less sensitivity to oxidation that are distinctly different from inorganic materials. By means of density-functional theory calculations, we systematically investigate the electronic and topological properties of a class of 2D MOFs X(C21H15N3) (X = transition metal element from 3 d to 5 d). Excitingly, we find that X(C21H15N3) (X = Ti, Zr, Ag, Au) are Chern insulators with sizable band gaps (∼7.1 meV). By studying a four-band effective model, it is revealed that the Chern insulator phase in X(C21H15N3) (X = Ti, Zr, Ag, Au) is caused cooperatively by the band inversion of the p orbitals of the C21H15N3 molecule and the intrinsic ferromagnetism of X(C21H15N3). Additionally, Mn(C21H15N3) is a Dirac half-metal ferromagnet with a high Curie temperature up to 156 K. Our work demonstrates that 2D MOFs X(C21H15N3) are good platforms for realizing the quantum anomalous Hall effect and designing spintronic devices based on half-metals with high-speed and long-distance spin transport.

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