A hidden constant in the anomalous Hall effect of a high-purity magnet MnSi

TL;DR

This study investigates the anomalous Hall effect in high-purity MnSi, revealing a hidden constant in the Hall conductivity that is independent of temperature and magnetic field, challenging existing theories.

Contribution

It uncovers a previously unnoticed constant in the anomalous Hall conductivity of MnSi, providing new insights into the underlying mechanisms.

Findings

The anomalous Hall conductivity is linearly proportional to magnetization.

The proportionality constant remains constant across a wide temperature range.

The constant persists despite large changes in ordinary Hall conductivity.

Abstract

Measurements of the Hall conductivity in MnSi can provide incisive tests of theories of the anomalous Hall (AH) effect, because both the mean-free-path and magnetoresistance (MR) are unusually large for a ferromagnet. The large MR provides an accurate way to separate the AH conductivity $\sigma_{xy}^A$ from the ordinary Hall conductivity $\sigma_{xy}^N$. Below the Curie temperature $T_C$, $\sigma_{xy}^A$ is linearly proportional to $ M$ (magnetization) with a proportionality constant $S_H$ that is independent of both $T$ and $H$. In particular, $S_H$ remains a constant while $\sigma_{xy}^N$ changes by a factor of 100 between 5 K and $T_C$. We discuss implications of the hidden constancy in $S_H$.