Electric Field-Induced Modification of Magnetism in Thin-Film Ferromagnets

Abstract

A large electric field at the surface of a ferromagnetic metal is expected to appreciably change its electron density. In particular, the metal's intrinsic magnetic properties, which are commonly regarded as fixed material constants, will be affected. This requires, however, that the surface has a strong influence on the material's properties, as is the case with ultrathin films. We demonstrated that the magnetocrystalline anisotropy of ordered iron-platinum (FePt) and iron-palladium (FePd) intermetallic compounds can be reversibly modified by an applied electric field when immersed in an electrolyte. A voltage change of -0.6 volts on 2-nanometer-thick films altered the coercivity by -4.5 and +1% in FePt and FePd, respectively. The modification of the magnetic parameters was attributed to a change in the number of unpaired d electrons in response to the applied electric field. Our device structure is general and should be applicable for characterization of other thin-film magnetic systems.

Magnetoelectric coupling at metal surfaces

“…In 2003, Weissmüller et al found a reversible surfacecharge-induced strain in non-magnetic platinum [9]. The first experimental evidence for an electric-field-induced change of the magnetic properties of a metallic thin film was given by Weisheit et al [11]. They observed a variation of a few percent in the coercive field of FePt and FePd films under the application of electric fields (see Fig.…”

“…The idea of electric-field-induced magnetization reversal in metal thin films was theoretically first described by Blügel in 2000 [10]. The first experimental evidence for an influence of an electric field on the magnetism of a metal thin film was given by Weishaupt et al [11]. In ultrathin FePt films, they found a change of the coercivity of 4.5 % under the application of electric 1 Introduction fields.…”

Non-volatile electrically-driven repeatable magnetization reversal with no applied magnetic field

“…Demonstrating electrical control of coercivity 19,24 , exchange bias 25,26 or magnetic anisotropy 20,27 is insufficient because, respectively, an electrically addressable coercivity is inextricably linked with an applied magnetic field; because exchange bias is an interfacial phenomenon that cannot readily drive magnetization reversal throughout a film of significant thickness; and because no new magnetic anisotropy axis can lie more than 901 from the anisotropy axis along which the local magnetization initially lies. It has been suggested that this latter challenge may be overcome by applying a suitable sequence of normal stresses near the pre-existing magnetic anisotropy axes of a small homogeneously magnetized Stoner-Wohlfarth particle 28,29 , but this has not been experimentally realised.…”

Ferroelectric Control of Magnetocrystalline Anisotropy at Cobalt/Poly(vinylidene fluoride) Interfaces

“…Experimentally, it was shown that the MCA of FePt and FePd films immersed in an electrolyte can be modified by a few percent in an applied electric field. 11 A strong effect of applied electric field on the interface MCA was demonstrated for the Fe/MgO (001) interfaces. 12 Magnetic easy axis manipulation by electric field was also achieved in the (Ga,Mn)As magnetic semiconductor.…”