Observation of topological Hall effect in amorphous Fe/Gd heterostructures with asymmetric Bloch-type domain wall chirality population.

The non-trivial topological nature of chiral magnetic spin textures results in novel electromagnetic properties, such as the topological Hall effect (THE) which commonly appears as an anomaly in the Hall resistivity. So far, the THE has been primarily observed in magnetic crystals lacking inversion symmetry (e.g. MnSi [1], MnGe [2], SrRuO₃-SrIO₃[3]). In these systems, the magnetic spin textures possess a single Bloch- or Néel-type chirality that is set by either a bulk or an interfacial antisymmetric exchange interaction, commonly known as Dzyaloshinskii–Moriya interaction.

We report the observation of a THE in amorphous rare-earth transition-metal heterostructures with perpendicular magnetic anisotropy that possess a coexistence of left and right chiral Bloch-type domain walls with unequal population distribution. A combination of real-space observations by Lorentz TEM, magnetometry and transport measurements reveal one can engineer amorphous thin-film materials with a controllable THE, as will be discussed, based on temperature dependent studies on several heterostructures.

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[2] N. Kanazawa, et al. Phys. Rev. Lett. 106, 156603 (2011).
[3] J. Matsuno, et al. Sci. Adv. 2, e1600304 (2016).