Magnetic fingerprint of interfacial coupling between CoFe and nanoscale ferroelectric domain walls

TL;DR

This study investigates the magnetic coupling at the interface of CoFe and BiFeO3 thin films, revealing how different ferroelectric domain walls influence exchange bias, with implications for multiferroic device design.

Contribution

It introduces a magnetic fingerprinting method using FORC to distinguish contributions of various ferroelectric domain walls to exchange bias in CoFe/BFO heterostructures.

Findings

109° and charged domain walls significantly enhance exchange bias.

71° domain walls mainly increase coercivity, not exchange bias.

A varying-anisotropy model explains the exchange bias enhancement.

Abstract

Magnetoelectric coupling in ferromagnet/multiferroic systems is often manifested in the exchange bias effect, which may have combined contributions from multiple sources, such as domain walls, chemical defects or strain. In this study we magnetically "fingerprint" the coupling behavior of CoFe grown on epitaxial BiFeO3 (BFO) thin films by magnetometry and first-order-reversal-curves (FORC). The contribution to exchange bias from 71{\deg}, 109{\deg} and charged ferroelectric domain walls (DWs) was elucidated by the FORC distribution. CoFe samples grown on BFO with 71{\deg} DWs only exhibit an enhancement of the coercivity, but little exchange bias. Samples grown on BFO with 109{\deg} DWs and mosaic DWs exhibit a much larger exchange bias, with the main enhancement attributed to 109{\deg} and charged DWs. Based on the Malozemoff random field model, a varying-anisotropy model is proposed to account for the exchange bias enhancement. This work sheds light on the relationship between the exchange bias effect of the CoFe/BFO heterointerface and the ferroelectric DWs, and provides a path for multiferroic device analysis and design.