Peculiarities of the giant magnetoimpedance in permalloy-based film structures in the important temperature range for practical applications

Multilayer structures based on Fe$_{19}$Ni$_{81}$ films have been obtained by ion-plasma sputtering and investigated on an impedance spectroscopy apparatus equipped with a temperature unit. An increase in the magnetoimpedance ratios for the total impedance and its real part has been found for the multilayer structure (Cu/FeNi)$_{5}$/Cu/(Cu/FeNi)$_{5}$ upon heating from 25 to 50$^\circ$C. The maximum of the giant magnetoimpedance ratio of the total impedance $\Delta Z/Z$ = 56% has been observed at a frequency of 80 MHz with a sensitivity of 18%/Oe, while the maximum of the real part $\Delta R/R$ = 170% was observed at the frequency of 10 MHz with the sensitivity of 46%/Oe. Magnetization and resistivity at the direct current have been found to depend insignificantly on the temperature and, hence, the relaxation mechanism due to the magnetoelastic anisotropy was proposed as the most probable mechanism of increasing the value and sensitivity of the magnetoimpedance effect.