Magnetic Weyl semimetals and nodal line materials

Recently the combination of magnetism and topology is a new exciting direction in condensed matter physics [1,2]. In magnetic materials the Berry curvature and the classical AHE helps to identify interesting candidates. Magnetic ferromagnetic Heusler compounds were predicted and already identified as Weyl semimetals and nodal line materials such as Co₂YZ [3-6] (Y=Ti, Mn; Z=Ge, Sn, Ga, Al). Kagome lattice compounds are another tunable class and ferromagnetic Co₃Sn₂S₂ is a more 2D Weyl semimetal [7-9]. Beside the smoking gun experiments: Fermi arc and chiral anomaly [6,8,9] all these materials show giant responses: an anomalous Hall and an anomalous Nernst effect [10-13]. Beloposki et al. observed nodal lines and the related drum head surface states in Co₂MnGa via angle-resolved photoemission spectroscopy [5]. In Co₂MnAl a large AHE was already observed in 2011, with an application for anomalous Hall effect sensors in mind . The anomalous Hall effect in Co₂MnGa and Co₂MnAl is large, leading to a Hall angle of 12% and 21 %, respectively [11,13].

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