Large magnetodielectric effect based on spin-dependent charge transfer in metal-insulator type Co-(BaF_2) nanogranular films

摘要

Cobalt-metal-fluoride nanogranular films exhibit high electrical resistivity (ρ) and high permittivity (ε') as well as high magnetic moments, making them potentially suitable for applications in low power magnetoelectronic devices at a high-frequency range. Here, we present the DC/AC magnetoelectric effect of high-ρCo_x-(BaF_2)_(1-x) nanogranular films that are constituted of Co nanogranules of about 2 nm in diameter in an insulating BaF_2 crystal. Under the application of magnetic field (H), we observed the ρ variations (Δρ/ρ_0) of 2.0%-5.9% for x ranging 0.19-0.54 and the ε' variations (Δε/ε_0') of 0.7%-6.0% for x ranging 0.19-0.42, respectively. These magnetically controllable p and ε' are realized based on the spin-dependent quantum-mechanical charge transfer. The Co_x-(BaF_2)_(1-x) film for x = 0.42 possesses high ρ, while remaining in a notably high Δε/ε_0' of 6% at a megahertz frequency range. This study demonstrates a candidate of high-resistive magnetoelectric nanogranular films, which may bring prosperous applications in high-frequency magnetoelectric devices with low power consumption.