We have demonstrated the frequency dependence of the tunnel-type magneto-dielectric (TMD) effect in superparamagnetic Cox−(MgF2)1–x granular nanostructures by precise variations of x from 0.06 to 0.2. The structures consist of the nanometer-sized Co granules embedded in a crystallized MgF2 dielectric matrix. We observed an increased peak dielectric change Δe′/e′0 from 0.8% to 3% at a specific frequency fTMD, and tunable fTMD was achieved from 8 kHz to 6.6 MHz by increasing x. Theoretical fittings predict that the narrow distribution of relaxation time gave rise to an enhanced Δe′/e′0 and the narrowing of fTMD; the position variation of fTMD was attributed to the change in the intergranular distance between a pair of two neighboring granules. This study may help understand the fundamental physics between the TMD effect and nanometric structure and indicate that the films may work at higher frequency for devices with tunable dielectrics.

中文翻译：

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不同Co含量Co-MgF2颗粒膜隧道型磁介电效应的可调频率响应

我们已经通过 x 从 0.06 到 0.2 的精确变化证明了超顺磁性 Cox−(MgF2)1-x 颗粒纳米结构中隧道型磁介电 (TMD) 效应的频率依赖性。该结构由嵌入结晶 MgF2 介电基质中的纳米尺寸 Co 颗粒组成。我们观察到在特定频率 fTMD 下峰值介电变化 Δe'/e'0 从 0.8% 增加到 3%，并且通过增加 x 从 8 kHz 到 6.6 MHz 实现了可调 fTMD。理论拟合预测弛豫时间的窄分布导致Δe'/e'0增强和fTMD变窄；fTMD 的位置变化归因于一对两个相邻颗粒之间的晶间距离的变化。