The anti-ordinary Hall effect in NiPt thin films

TL;DR

This paper investigates the anomalous Hall effect in NiPt thin films, revealing an unusual 'anti-ordinary' Hall effect near a quantum critical point caused by Berry phase singularities.

Contribution

It demonstrates the tunability of the sign of the extraordinary Hall effect in NiPt alloys near a ferromagnetic quantum critical point, linking it to Berry phase effects.

Findings

Ordinary Hall effect is negative across all compositions.

Extraordinary Hall effect is negative except near the critical point.

Sign of the extraordinary Hall effect can be switched by temperature or composition.

Abstract

We study the anomalous Hall effect in binary alloys between the group-10 elements Ni and Pt. It is observed that the ordinary Hall effect is negative (electron-like) at any composition of the alloy. The extraordinary Hall effect is also negative except in the vicinity of the ferromagnetic quantum critical point. Close to the critical point the sign of the extraordinary Hall effect can be changed to positive (hole-like) by tuning either the temperature or the composition of the alloy. We attribute such an "anti-ordinary" Hall effect with opposite signs of the ordinary and the extraordinary contributions to a Berry phase singularity, moving away from the Fermi energy with increasing the ferromagnetic exchange energy.