Temperature–frequency dependence of the dielectric response in LuFe$_{2}$O$_{4}$ multiferroics

The temperature–frequency spectra of the complex dielectric permittivity of the LuFe$_{2}$O$_{4}$ multiferroics have been studied in the temperature range 100–400 K at frequencies 20 Hz–120 MHz. It is found that the temperature coefficient of the dielectric permittivity changes its sign and the ac conductivity has maxima and minima in the temperature range $\sim$150–350 K and in the frequency range $\sim$30–120 MHz. These specific features are due to independent resonance mechanisms: the coincidence of frequency of the measuring ac voltage with the frequency of electron jumps as the hopping conductivity takes place; the proximity of the measurement signal period to the time of formation of a barrier layer at the boundary of contact with the sample; and the approximation of the frequency of an ac external field to the frequency of the sample structural elements.