Origin of the topological/unconventional Hall effect in Quaternary Heusler alloy NiCoMnAl.

Non-trivial spin configurations such as skyrmions and anti-skyrmions have gained attention owing to their importance from fundamental and technological perspective. Heusler alloy is one such family of compound with promising characteristics for exploring and controlling topological phases. Albeit of existing literature on topologically spin structures in full and inverse Heusler compound, the subgroup of quaternary Heusler alloy remains unexplored. In this study, the novel quaternary Heusler alloy NiCoMnAl is interesting as the obtained saturation moment deviates from the theoretical prediction. The ac susceptibility measurement also reveals the presence of non-coplanar (NPL) spin textures before the field polarized phase. The transverse resistivity measurements reflect the presence of non-trivial spin arrangement where an additional component [i.e. topological Hall resistivity (THR)/unconventional Hall resistivity (UCHR)] with anomalous Hall resistivity (AHR) arises in a temperature range of 2-380 K, with a considerable value of 2.5µΩ cm at 300 K. We propose to investigate the magnetic spin configuration of polycrystalline NiCoMnAl in zero-field as well as in presence of external applied magnetic fields in the wide temperature range to confirm the formation of topologically protected textures and skyrmion lattice formation by SANS experiment.