Origin of Anomalous Hall effect in Cr-doped RuO$_2$

TL;DR

This paper revises previous interpretations of the anomalous Hall effect in Cr-doped RuO$_2$, showing it originates from Cr ions rather than altermagnetism, based on density functional calculations that challenge earlier experimental conclusions.

Contribution

The study provides a new interpretation of the AHE in Cr-doped RuO$_2$, demonstrating it is caused by Cr ions instead of altermagnetism, based on revised density functional analysis.

Findings

Extra holes bind to Cr impurities, not doping Ru bands.

RuO$_2$ remains nonmagnetic without doping.

AHE arises from Cr ions, not altermagnetism.

Abstract

RuO$_2$ is one of the most highlighted candidates for altermagnetism. However, the most recent muon spin spectroscopy and neutron studies demonstrated the absence of magnetic order in this system. The electronic structure of RuO$_2$ hints at a possibility of realizing a magnetically ordered state upon hole doping, and such a possibility was explored experimentally in Cr-doped RuO$_2$, where it was suggested that this system exhibits the anomalous Hall effect (AHE) due to altermagnetism. In this manuscript, based on our density functional calculations, we revise the results obtained for this system and propose a different interpretation of experimental results. Our calculations suggest that extra holes are bound to Cr impurity and do not dope Ru bands, which remain nonmagnetic. Thus, the observed AHE is not due to the altermagnetism but stems entirely from magnetic Cr ions.