Large tunneling magneto-dielectric enhancement in Co(Fe)-MgF₂granular films by minor addition of Si

We report a large enhancement of the tunneling magneto-dielectric (TMD) effect in Co-MgF2 granular films induced by doping using a small amount of Si. This minor addition of Si is dispersed uniformly in the MgF2 matrix and acts by inhibiting the interdiffusion between the Co and MgF2 phases, thus enhancing the magnetization when compared with the case of the corresponding undoped Co-MgF2 films; this consequently results in a greatly enhanced peak dielectric variation (TMD ratio, Δϵ′/ϵ′), as indicated by theoretical fittings. Extension of this Si doping effect to CoFe-MgF2 films led to a record-high Δϵ′/ϵ′ of 4.3% at 10 kHz and 8.5% at 200 kHz under the application of a magnetic field (H) of 10 kOe, while remaining as high as 2.1% even under H = 1 kOe. This study presents a simple but highly effective approach to enhance the TMD effect in granular nanocomposites, thus opening up the prospect of development of high-performance magnetoelectric devices.