Electric-field-induced magnetization changes in Co/Al2O3 granular multilayers

TL;DR

This study investigates how electric fields influence magnetization in Co/Al2O3 granular multilayers, revealing reversible and irreversible regimes linked to electronic and ionic effects, supported by experimental and theoretical analysis.

Contribution

It provides a combined experimental and theoretical analysis of electric field effects on magnetization in granular multilayers, highlighting reversible electronic and irreversible ionic mechanisms.

Findings

Reversible magnetization changes due to electronic band structure modifications.

Irreversible magnetization decrease caused by oxygen migration and increased oxidation.

Theoretical model explains electric field-induced band structure alterations.

Abstract

We study experimentally the effect of electric field on the magnetization of Co/Al2O3 granular multilayers. We observe two distinct regimes: (a) low-field regime when the net magnetization of the system changes in a reversible way with the applied electric field and (b) high-field regime when the magnetization decreases irreversibly. The former is attributed to the changes in the relative 3d-orbital occupation of the minority and majority bands in the Co granules. A theoretical model has been developed to explain the electric field induced changes in the band structure of the granular system and hence the magnetic moment. The latter result may be understood assuming the electric field induces oxygen migration from Al2O3 to the Co granules, since an increase in oxidation state of the Co granules is shown, through ab-initio calculations, to give rise to a reduced magnetization of the system.