Large negative magnetoresistance in BaMn$_2$Bi$_2$ antiferromagnet

TL;DR

This study reports a large negative magnetoresistance in BaMn$_2$Bi$_2$, where magnetic fields induce a transition from insulating to metallic behavior without magnetic phase changes, linked to conduction sensitivity to magnetic canting.

Contribution

It reveals a novel magnetoresistance effect in BaMn$_2$Bi$_2$ driven by magnetic field-induced conduction changes without phase transitions.

Findings

LNMR observed in insulating BaMn$_2$Bi$_2$ under perpendicular magnetic field

Magnetic field suppresses insulating state, induces metallic behavior

Hall effects indicate conduction sensitivity to magnetic canting

Abstract

A very large negative magnetoresistance (LNMR) is observed in the insulating regime of the antiferromagnet BaMn$_2$Bi$_2$ when a magnetic field is applied perpendicular to the direction of the sublattice magnetization. High perpendicular magnetic field eventually suppresses the insulating behavior and allows BaMn$_2$Bi$_2$ to re-enter a metallic state. This effect is seemingly unrelated to any field induced magnetic phase transition, as measurements of magnetic susceptibility and specific heat did not find any anomaly as a function of magnetic fields at temperatures above $2\,\mathrm{K}$. The LNMR appears in both current-in-plane and current-out-of-plane settings, and Hall effects suggest that its origin lies in an extreme sensitivity of conduction processes of holelike carriers to the infinitesimal field-induced canting of the sublattice magnetization. The LNMR-induced metallic state may thus be associated with the breaking of the antiferromagnetic parity-time symmetry by perpendicular magnetic fields and/or the intricate multi-orbital electronic structure of BaMn$_2$Bi$_2$.