Observation of Topological Hall Effect in A Chemically Complex Alloy.

Topological Hall effect is the transport response of chiral spin textures, thus can serve as a powerful probe for detecting and understanding these unconventional magnetic orders. So far, the topological Hall effect has been only observed in either noncentrosymmetric systems where spin chirality is stabilized by Dzyaloshinskii-Moriya interactions, or triangular-lattice magnets with Ruderman-Kittel-Kasuya-Yosida-type interactions. Here, we observed a pronounced topological Hall effect in a Fe-Co-Ni-Mn chemically complex alloy with a simple face-centered cubic (fcc) structure across a wide range of temperature and magnetic field. The alloy is shown to have a strong magnetic frustration owing to the random occupation of magnetic atoms on the close-packed fcc lattice and the direct Heisenberg exchange interaction among atoms, as evidenced by the appearance of a reentrant spin glass state in the low temperature regime and the first principles calculations. Consequently, the topological Hall effect is attributed to the nonvanishing spin chirality created by strong spin frustration under the external magnetic field, which is distinct from the mechanism responsible for the skyrmion systems, as well as geometrically frustrated magnets. This article is protected by copyright. All rights reserved.