Tunnel-Type Magneto-Dielectric Effect and Its Annealing Study in Co–SiO₂ Granular Films

Abstract

Tunnel-type magneto-dielectric (TMD) effect arising from the spin-dependent quantum tunneling between nano-sized granular pairs, has opened up new route for room temperature magnetoelectric fields. We first investigated the TMD properties in metal-oxide (Co–SiO₂) granular films and their annealing effect in this work. Results show that the films exhibit a TMD ratio () of 1% with high electrical resistivity of >10⁸ µΩ·m and intermediate optical transmittance in Co_0.24–(SiO₂)_0.76 films. Annealing investigations suggest that the samples remain TMD response up to 573 K, and further increment in annealing temperature leads to the inter-diffusion between Co and SiO₂ interfaces, thus producing the increasing oxidation of metallic Co. This study demonstrates the possibility of TMD effect in metal-oxide composite materials, and may be desirable for a variety of other wide oxide-based candidates for magnetoelectric device applications.

Fig. 3 (a) Frequency dependence of the real part of dielectric constants for x = 0.24, with and without the application of magnetic field H = 800 kA/m; inset presents the detail of dielectric difference Δε' = ε'_H - ε'₀ between dielectric constants ε′ with and without magnetic field. (b) Frequency dependence of the magneto-dielectric response Δε'/ε'₀ for various x values from 0.12 to 0.24; insets show the pictures of films deposited on quartz (SiO₂) substrate, which may reflect their optical transmittance of 450-nm-thick films with different Co concentration from 0.12 to 0.27.