Figure 6. Magnetocapacitance effect in Bi_4.2K_0.8Fe₂O_9+δ nanobelts.

(a–b) Temperature dependence of dielectric constant ε′ (a), and dielectric loss tan_δ (b) of the bulks made of the Bi_4.2K_0.8Fe₂O_9+δ nanobelts at 1 kHz, 10 kHz, 50 kHz, 100 kHz, 500 kHz and 1 MHz measured in zero magnetic field. (c) Temperature dependence of ε′ at 1 kHz under zero (red points) and 50 kOe (olive points) magnetic fields, respectively. The inset of (c) shows the temperature profiles of dc resistivity ρ at zero (red line) and 50 kOe (olive line), respectively. (d) The corresponding temperature dependence of the magnetocapacitance effect of the samples.