Leider fällt der Vortrag von Prof. Anna Isaeva, Technische Universität (TU) Dortmund, am Montag, den 25. November 2024, 17.00 Uhr s.t. im HS 04 (F.10.01) über "Atomic Intermixing as a Tool to Design the Magnetic Ground State in Magnetic Topological Insulators" aus!

Abstract

Anna Isaeva,1,2,3 Ekaterina Kochetkova,1,2 Manaswini Sahoo,2 Falk Pabst,1 Marie Tardieux,1 Laura T. Corredor,2 Irene Aguilera1

1 University of Amsterdam, The Netherlands
2 Leibniz IFW Dresden, Germany
3 University of Dortmund, Germany

Magnetic topological materials are a hotbed for exotic quantum phenomena such as the quantum anomalous Hall effect (QAHE), the topological magneto-electric effect, new topological states like axion insulators and magnetic Weyl semimetals. In reply to the high demand for optimized material systems, magnetic topological insulators made a decade-long journey [1] from extrinsically doped Bi2Te3 and (Cr,V)Bi2(Se,Te)3 heterostructures, on which the QAHE was experimentally discovered [2], to the intrinsically magnetic van der Waals material MnBi2Te4 [3]. The QAHE was observed in MnBi2Te4 thin films at notably higher temperatures of 6 K [4] than in [2], pointing at a perspective pathway of materials optimization towards more robust quantum effects. Since the bulk MnBi2Te4 is an A-type antiferromagnet with TN = 25 K, the task of fabricating structurally similar ferri- or ferromagnets with an increasing TC is pertinent.

MnBi2Te4 is the progenitor of a family of van der Waals materials (MnX2Te4)(X2Te3)n, X = Sb or Bi, n = 0–4, which I will introduce in my talk. Their crystal lattices are ordered stacking variants of septuple (MnX2Te4) layers hosting an ordered magnetic sublattice of Mn(II) atoms and of n quintuple (X2Te3) spacers. Varying intralayer and interlayer magnetic exchange couplings foster a rich palette of possible magnetic ground states, including ferri- and ferromagnetic. Besides the stacking order, a more subtle factor – Mn/X site intermixing [5] – influences the long-range magnetic order greatly. This phenomenon is particularly prominent in Mn1±xSb2Te4 where it raises the Curie temperature of a ferrimagnetic-to-paramagnetic transition from 27 to 58 K, while x varies in the range of 0.1–1.0 [6-9]. At higher x values, we document a structure transition to the cubic lattice symmetry in Mn2.7Sb1.3Te4 and Mn2.1Ge0.4Sb0.9Te4 which alters the band topology and magnetic order notably. Mn-enrichment results in very different ground states: whereas Mn2.7Sb1.3Te4 is a ferromagnet with the record high TC = 73 K, that bring magnetic topological materials close to the liquid nitrogen limit, Mn2.1Ge0.4Sb0.9Te4 is an antiferromagnet with TN = 25 K. With an aid of the ab initio calculations we look into the origins of this strong difference.

REFERENCES

[1] Y. Tokura et al. Nature Reviews Physics 1, 126 (2019). [2] C.-Z. Chang et al. Science 340, 167 (2013). [3] M. Otrokov, … A. Isaeva, E.V. Chulkov. Nature 576, 416 (2019) ; [4] Y. Deng et al. Science 367, 895 (2020); [5] A. Zeugner, …, A. Isaeva. Chem. Mater. 31, 2795 (2019) ; [6] Y. Liu et al. Phys. Rev. X 11, 021033 (2021); [7] S. Wimmer et al. Adv. Mater. 33, 2102935 (2021) ; [8] L. Folkers, … A. Isaeva. Z. Krist. 237, 2057 (2021); [9] M. Sahoo, … A. Isaeva. Mater. Today Phys. 38, 101265 (2023).