Exchange Field-Mediated Magnetoresistance in the Correlated Insulator Phase of Be Films

TL;DR

This study demonstrates that an exchange field induced by a ferromagnetic insulator can produce significant low-field magnetoresistance in highly disordered, correlated insulator phase beryllium films, regardless of their disorder level.

Contribution

It reveals that the exchange field from EuS induces a robust magnetoresistance in Be films across a wide range of disorder levels, including the correlated insulator phase.

Findings

Exchange field $H_{ex}$ persists in high resistance Be films.

$H_{ex}$ is relatively insensitive to Be disorder.

Giant low-field magnetoresistance observed in the correlated insulator phase.

Abstract

We present a study of the proximity effect between a ferromagnet and a paramagnetic metal of varying disorder. Thin beryllium films are deposited onto a 5 nm-thick layer of the ferromagnetic insulator EuS. This bilayer arrangement induces an exchange field, $H_{ex}$, of a few tesla in low resistance Be films with sheet resistance $R\ll R_Q$, where $R_Q=h/e^2$ is the quantum resistance. We show that $H_{ex}$ survives in very high resistance films and, in fact, appears to be relatively insensitive to the Be disorder. We exploit this fact to produce a giant low-field magnetoresistance in the correlated insulator phase of Be films with $R\gg R_Q$.