AC magnetic susceptibility of nanocomposites with Co-Pd particles

Abstract

Frequency and magnetic field dependences of the dynamic AC susceptibility of nanocomposites based on opal matrixes with Co and Pd particles have been experimentally investigated in the temperature range from 1.8 to 300 K at several frequencies of alternating magnetic field. Comparative analysis of the magnetic field dependences of the differential DC and dynamic AC susceptibilities has been carried out. The hysteresis loops of the nanocomposite samples were measured, as well as their structure and phase composition were studied. The magnetic field dependences of the differential DC susceptibility have been found to be close to the field dependences of the dynamic AC susceptibility measured at the frequency of 1 Hz but substantially differ from the susceptibility measured at the frequency of 10 Hz and higher. This fact indicates that long relaxation times exceeding ∼ 1 s are characteristic of the substance (Co + Pd). The frequency dependences of the dynamic AC susceptibility were used to calculate the relaxation times with the Cole-Cole formula. The sample with hexagonal Co and metallic Pd has been found to have three relaxation times of about 10-3, 10-2 and 1 s. At that, the field dependences of the differential DC susceptibility differ from the field dependences of the dynamic AC susceptibility measured at the frequencies of 10, 100 Hz and 1 kHz, which, in turn, are close to each other. This means that the eddy current losses are small in comparison with the magnetization reversal losses.