Imaging of magnetic domains in ferromagnetic Weyl semimetal Co2MnGa

Semimetals are a wide range of materials filling the gap between classical metals and semiconductors. Unlike in semiconductors, in a semimetal the conduction and valence bands have a small overlap, but similarly to semiconductors, the charge transfer in semimetals is governed by both electrons and holes. Electron and hole transport properties are defined by the respective band structures. Lately a class of semimetals was discovered, in which the crossing between the conduction and valence bands takes place in single points (Weyl nodes) in momentum space. The electrons with Fermi energies close to these nodes behave like relativistic particles – Weyl fermions. These have distinct dispersion and chirality properties, which can give rise to a multitude of exotic transport phenomena.

A subclass of Weyl semimetals are magnetic Weyl semimetals, where the ferromagnetic structure together with the strong spin-orbit coupling create Weyl nodes¹. In magnetic Weyl semimetals due to broken both inversion symmetry and time-reversal symmetry exist a number of exotic transport properties, such as negative magnetoresistance, anomalous Hall effect, or anomalous Nernst effect² (ANE) – an electrical field perpendicular to both magnetization and temperature gradient. Materials with strong ANE are interesting for spintronics applications, where the logic is built not on charge, but on spin of the carriers – which is more favorable from the energy-saving point of view, as the heat generated by other parts of the circuit can be re-used. Co₂MnGa is a strong candidate for magnetic Weyl semimetal that exhibits such a strong ANE. In a recent publication³ researchers studied local anomalous Nernst effect using atomic force microscope where the temperature gradient was created using an AFM tip and the magnetic field was generated by a variable magnetic field sample holder. With this technique they have mapped the magnetic domains in a nanowire made of Co₂MnGa.

1. Liu et al., Science 365, (2019) 1282–1285
2. Sakai et al., Nat. Phys. 14, (2018) 1119
3. Budai et al., Appl. Phys. Lett. 122, (2023) 102401

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