# Seminar - Claudia Felser, Max Planck (Dresden), “Heusler compounds: Tunable materials with non-trivial topologies”

Mon, Apr 11, 2016, 4:30 pm to 5:30 pm
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Event Location: Taylor Auditorium, Frick Chemistry Laboratory Heusler compounds are a remarkable class of materials with more than 1,000 members and a wide range of extraordinary multifunctionalities [1] including tunable topological insulators (TI) [2]. The tunabilty of this class of materials is exceptional and nearly every functionality can be designed [1] ranging from wide band gap semiconductors to hard magnetic ferrimagnetic metals. There are two classes of Heusler compounds: half Heusler XYZ and Heusler X2YZ compounds, where Z is a main group metal and X and Y are transition metals. Many of the XYZ compounds are semiconductors or topological semimetals [2]. The ternary zero-gap semiconductors (LnAuPb, LnPdBi, LnPtSb and LnPtBi) contain the rare-earth element Ln, which can realize additional properties ranging from superconductivity (for example LaPtBi) to magnetism (for example GdPtBi) and heavy fermion behavior (for example YbPtBi). These properties can open new research directions in realizing the quantized anomalous Hall Effect and topological superconductors. C1b Heusler compounds have been grown as single crystals and as thin films. The control of the defects, the charge carriers and mobilities can be optimized [3]. The band inversion was observed by angle resolved photoemission spectroscopy [4]. Dirac cones and Weyl points can occur at the critical points in the phase diagrams of TI or can be induced via a magnetic field in all magnetic Heusler compounds with an inverted band structure [5]. Co2YZ and Mn2YZ Heusler compounds play an important role for future spintronic devices because of their half-metallic band structure [1]. Recently a high spinpolarisation for spintronic applications was proven by spin resolved photoemission [6]. The Curie temperature are far above room temperature, up to 1200 K. Manganese-rich Heusler compounds are attracting interest in the context of spin transfer torque based data storage [7,8], spin Hall effect, non collinear magnetism [9] and rare-earth free hard magnets. The Mn3+ ions in Mn2YZ cause a Jahn Teller distortion [7,10]. Tetragonal Heusler compounds with large magneto crystalline anisotropy can be easily designed by positioning the Fermi energy at a van Hove singularity in one of the spin channels. Because of the ferrimagnetic arrangement of the sublattices, artificial antiferromagnets can be designed in Mn2YZ Heusler compounds. New properties can be observed such as, large exchange bias, non-collinear magnetism topological Hall effect, spin gapless semiconductivity and Skyrmions [9, 11-13]. Weyl points and the corresponding Berry phase induce in Mn3Ge a giant anomalous Hall effect [14]. [1] Graf, et al., Progress in Solid State Chemistry 39 1 (2011). [2] Chadov, et al., Nature Mater. 9,541 (2010) and Lin, et al., Nature Mater. 9, 546 (2010) [3] Shekhar, et al., Physical Review B 86 155314 (2012) [4] Liu, et al., Nature Communication under review, arXiv:1602.05633 [5] Hirschberger et al. arXiv:1602.07219 [6] Jourdan, et al, Nature Com. 5 3974 (2014). [7] Winterlik, et. al., Adv. Mat. 24 6283 (2012). [8] Jeong, et al., Nature Com. 7 10276 (2016) [9] Meshcheriakova, et al., Phys. Rev. Lett. 113 087203 (2014) [10] Wollmann, et al. Phys. Rev. B 92 064417 (2015) [11] Nayak, et al. Phys. Rev. Lett. 110 127204 (2013) [12] Ouardi, et al., Phys. Rev. Lett. 110100401 (2013) [13] Nayak, et al., Nat. Mater. 14679 (2015) [14] Nayak, et al., Science Adv. in press (2016)
Location: Taylor Auditorium, Frick Chemistry Laboratory