Tunnel magnetocapacitance in Fe/MgF₂ single nanogranular layered films

The tunnel magnetocapacitance (TMC) effect in two-dimensional single nanogranular layered $Fe/MgF2$ films is investigated both experimentally and theoretically. We measured the frequency dependence of TMC ratios in a frequency range of 20 Hz–1 MHz and discovered that TMC ratios strongly depend on the frequency, reaching a peak value at a specific frequency. We observe that the largest TMC ratios occur at lower frequencies and that TMC values steadily reduce with increasing frequency. Notably, we achieved a maximum TMC ratio of 1.45%, which is the largest low-field TMC ever reported for granular films. A combination of the Debye–Fröhlich (DF) model and the Julliere formula is used to fit the experimental data to theory, and an excellent agreement between the calculated values and the experimental data is obtained. To perfectly fit the experimental data, the conventional DF model is extended to a composite model in which three capacitors (with three different relaxation times) are introduced. Our findings will give further insights into the exact mechanism of the TMC effect in nanogranular films and will open broader opportunities for device applications, such as magnetic sensors and impedance tunable devices.