Observation of Topological Hall Effect in a Chemically Complex Alloy

Area of Science:

• Condensed Matter Physics
• Materials Science
• Magnetism

Background:

• The topological Hall effect (THE) probes chiral spin textures and unconventional magnetic orders.
• Previously, THE was observed only in noncentrosymmetric systems or triangular-lattice magnets.
• These systems rely on Dzyaloshinskii-Moriya interactions or RKKY interactions, respectively.

Purpose of the Study:

• To investigate the presence and origin of the topological Hall effect in a face-centered cubic (fcc) Fe-Co-Ni-Mn alloy.
• To explore the relationship between magnetic frustration and THE in this complex alloy.
• To differentiate the mechanism of THE in this system from those in skyrmion and geometrically frustrated magnets.

Main Methods:

• Experimental observation of THE in a Fe-Co-Ni-Mn alloy across various temperatures and magnetic fields.
• Analysis of magnetic properties, including the observation of a reentrant spin glass state.
• First-principles calculations to understand the electronic and magnetic structure.

Main Results:

• A pronounced topological Hall effect was observed in the fcc Fe-Co-Ni-Mn alloy.
• The alloy exhibits strong magnetic frustration due to random atomic occupation and Heisenberg exchange interactions.
• A reentrant spin glass state was identified at low temperatures, confirming magnetic frustration.

Conclusions:

• The observed THE in the Fe-Co-Ni-Mn alloy arises from spin chirality induced by magnetic frustration under an external magnetic field.
• This mechanism is distinct from those governing THE in skyrmion systems and geometrically frustrated magnets.
• The study demonstrates that complex alloys with simple structures can host unconventional magnetic phenomena like THE.