Mn‐Rich MnSb2Te4: A Topological Insulator with Magnetic Gap Closing at High Curie Temperatures of 45–50 K

• Published in: Advanced materials (Weinheim) 2021-10, Vol.33 (42), p.n/a
• Main Authors: Wimmer, Stefan, Sánchez‐Barriga, Jaime, Küppers, Philipp, Ney, Andreas, Schierle, Enrico, Freyse, Friedrich, Caha, Ondrej, Michalička, Jan, Liebmann, Marcus, Primetzhofer, Daniel, Hoffman, Martin, Ernst, Arthur, Otrokov, Mikhail M., Bihlmayer, Gustav, Weschke, Eugen, Lake, Bella, Chulkov, Evgueni V., Morgenstern, Markus, Bauer, Günther, Springholz, Gunther, Rader, Oliver
• Format: Article
• Language: English
• Subjects: 4; Antiferromagnetism; Antimony; Critical point; Curie temperature; Electrons; Energy gap; Ferromagnetism; Interlayers; Magnetic anisotropy; magnetic bandgap; magnetic topological insulators; Magnetism; magnetization; Manganese; Materials science; Mn-Sb site exchange; MnSb; MnSb 2Te 4; molecular beam epitaxy; Photoelectrons; Polarization (spin alignment); Quantum Hall effect; Qubits (quantum computing); Spectroscopy; Spectrum analysis; Spintronics; Te-2; Topological insulators
• ISSN: 0935-9648; 1521-4095; 1521-4095
• DOI: 10.1002/adma.202102935

Ferromagnetic topological insulators exhibit the quantum anomalous Hall effect, which is potentially useful for high‐precision metrology, edge channel spintronics, and topological qubits.  The stable 2+ state of Mn enables intrinsic magnetic topological insulators. MnBi2Te4 is, however, antiferromagnetic with 25 K Néel temperature and is strongly n‐doped. In this work, p‐type MnSb2Te4, previously considered topologically trivial, is shown to be a ferromagnetic topological insulator for a few percent Mn excess. i) Ferromagnetic hysteresis with record Curie temperature of 45–50 K, ii) out‐of‐plane magnetic anisotropy, iii) a 2D Dirac cone with the Dirac point close to the Fermi level, iv) out‐of‐plane spin polarization as revealed by photoelectron spectroscopy, and v) a magnetically induced bandgap closing at the Curie temperature, demonstrated by scanning tunneling spectroscopy (STS), are shown. Moreover, a critical exponent of the magnetization β ≈ 1 is found, indicating the vicinity of a quantum critical point. Ab initio calculations reveal that Mn–Sb site exchange provides the ferromagnetic interlayer coupling and the slight excess of Mn nearly doubles the Curie temperature. Remaining deviations from the ferromagnetic order open the inverted bulk bandgap and render MnSb2Te4 a robust topological insulator and new benchmark for magnetic topological insulators. Mn‐rich MnSb2Te4 is shown to exhibit ferromagnetic hysteresis with out‐of‐plane anisotropy and Curie temperature of 45–50 K. It is a topological insulator with Dirac point close to the Fermi level and a magnetic gap that closes at the Curie temperature. These favorable properties are caused by excess Mn that substitutes Sb within the septuple layers.