Heusler Compounds - C. Felser
In general, the material class under investigations – Heusler compounds with X2YZ with L21 and XYZ with C1b structure type – show the same broad variety of properties, including topological insulators, Weyl semimetals, Kondo behaviour, non-centrosymmetric superconductivity and conventional, tunable magnetic properties, including non-collinear magnetism, semiconductivity, magnetoresistance effects, Li-ion-conductivity, thermoelectricity and other physical properties.
Most Heusler compounds with C1b symmetry are ternary semiconductors and structurally and electronically strongly related to binary semiconductors. The band gap can be tuned from 4 eV to zero and more than 50 compounds show a band inversion. But in addition to the known applications for binary semiconductors, multifunctional properties are possible in this class of materials. For example, similar to the quantum spin Hall system CdTe/HgTe, quantum well structures with band inversion can be predicted for different Heusler compounds combinations such as LuPdSb/LuPtBi. Many of these ternary zero-band semiconductors also contain rare earth elements, which can induce a secondary property ranging from super-conductivity (e.g. LaPtBi) to antiferromagnetism (e.g. GdPtBi) and heavy fermion behavior (e.g. YbPtBi).
Magnetic Heusler compounds are well established in the field of spintronics, especially the half metallic ferromagnetic compounds with high Curie temperatures such as Co2FeSi and Co2MnSi. These compounds show a high spin polarization and Curie temperatures up to 1120K. Co2-Heusler compounds are centrosymmetric and therefore break time-reversal symmetry, so that crossing points in the band structure are potential Weyl points or nodal lines. Co2YZ (with Y = V, Zr, Nb, Ti, Hf; Z = Si, Ge, Sn, proposed by Bernevig and Dai 2015) and Co2MnZ (Z=Al, Ga proposed, by Kübler and Felser 2016) have all been predicted to be Weyl semimetals. The proof that Co2MnGa is a magnetic Weyl semimetal was obtained via angle-resolved photoemission spectroscopy (ARPES), by which nodal lines and the related drum-head surface states were observed. However, the cubic structure made it difficult to observe the chiral anomaly. Co2MnZ has Weyl nodes near the Fermi energy and, as a consequence, a giant AHE and a giant anomalous Nernst effect that stems from the divergent Berry curvature at the Weyl nodes. Co2MnGa exhibits one of the highest anomalous Hall conductivities, Nernst effects, and anomalous Hall angles amongst all known magnetic Heusler compounds at room temperature. Heusler compounds have natural advantages of high magnetic ordering temperatures, clearly defined topologically non-trivial band structures, low charge carrier densities, and strong electromagnetic responses, and thus show great promise for the study of quantum effects.
Inverse Heusler compounds such as Mn2YZ are excellent candidate for spin transfer torque devices, for compensated ferrimagnetism and can host Skyrmions. Two systems, hexagonal Mn3Sn and Mn3Ge (proposed by Felser and Kübler) have a non-collinear triangular antiferromagnetic structure that might be the origin of a non- vanishing Berry curvature that is observed in density functional theory calculations. Mn3Sn and Mn3Ge have Weyl points close to the Fermi energy and show the predicted properties with an AHE even at room temperature. The strong response of a Weyl semimetal to external stimuli makes these compounds promising candidates for topological antiferromagnetic spintronics.
Zwischen intermetallischen Verbindungen und Legierungen: Heusler-Verbindungen, J. Kroder, G. H. Fecher, C. Felser, Chemie in unserer Zeit, DOI: 10.1002/ciuz.202000063
Heusler, Weyl, and Berry, Kaustuv Manna, Yan Sun, Lukas Müchler, Jürgen Kübler, Claudia Felser, Nature Reviews Materials 3 (2018) 244
Simple Rules for the Understanding of Heusler Compounds, Tanja Graf, Stuart S. P. Parkin, and Claudia Felser, Progress in Solid State Chemistry 39 (2011) 1
Establishing the carrier scattering phase diagram for ZrNiSn-based half-Heusler thermoelectric materials, Qingyong Ren, Chenguang Fu, Qinyi Qiu, Shengnan Dai, Zheyuan Liu, Takatsugu Masuda, Shinichiro Asai, Masato Hagihara, Shuki Torri, Takashi Kamiyama, Lunhua He, Xin Tong, Claudia Felser, David J. Singh, Tiejun Zhu, Jiong Yang, Jie Ma, Nature Communications 11 (2020) 3142
Discovery of topological Weyl lines and drumhead surface states in a room-temperature magnet, Ilya Belopolski, Kaustuv Manna, Daniel S. Sanchez, Guoqing Chang, Benedikt Ernst, Su-Yang Xu, Songtian S. Zhang, Hao Zheng, Jiaxin Yin, Bahadur Singh, Guang Bian, Daniel Multer, Xiaoting Zhou, Shin-Ming Huang, Baokai Wang, Arun Bansil, Hsin Lin, Claudia Felser, and M. Zahid Hasan, Science 365 (2019) 1278
Anomalous Nernst effect beyond the magnetization scaling relation in the ferromagnetic Heusler compound Co2MnGa, Satya N. Guin, Kaustuv Manna, Jonathan Noky, Sarah J. Watzman, Chenguang Fu, Nitesh Kumar, Walter Schnelle, Chandra Shekhar, Yan Sun, Johannes Gooth, Claudia Felser, npg materials asia 11 (2019) 11
Magnetic antiskyrmions above room temperature in tetragonal Heusler materials, Ajaya K. Nayak, Vivek Kumar, Peter Werner, Eckhard Pippel, Roshnee Sahoo, Franҫoise Damay, Ulrich K. Rößler, Claudia Felser, Stuart S. P. Parkin Nature 548 (2017) 561
Large anomalous Hall effect driven by a nonvanishing Berry curvature in the noncolinear antiferromagnet Mn3Ge, A. K. Nayak, J. E. Fischer, Y. Sun, B. Yan, J. Karel, A. C. Komarek, C. Shekhar, N. Kumar, W. Schnelle, J. Kübler, C. Felser, S. S. P. Parkin, Science Advances 2 (2016) e1501870
Design of compensated ferrimagnetic Heusler alloys for giant tunable exchange bias, Ajaya K. Nayak, Michael Nicklas, Stanislav Chadov, Panchanana Khuntia, Chandra Shekhar, Michael Baenitz, Yurii Skourski, Veerendra K. Guduru, Alessandro Puri, Uli Zeitler, Claudia Felser, Nature Materials 14 (2015) 679