Impedance and magnetic properties of chemically synthesized CrO2∕Ag nanocomposite particles

Abstract

The impedance of CrO2∕Ag nanocomposite particles has been investigated in the frequency range of 100Hz–1MHz at a temperature of 300–475K. The impedance in the form of Cole-Cole plot reveals that the resistivity contribution primarily comes from bulk grain interior below 375K and above those from both the grain interior and grain boundaries. The grain interior resistance decreases from 163kΩ at 300Kto6kΩ at 475K with a typical semiconductor like behavior. Above 375K, the impurities at grain boundaries are thermally activated and, thus, contribute to the dielectric relaxation. The electrical conductivity of the CrO2∕Ag nanocomposite follows an Arrhenius law with an activation energy/dielectric transition from 0.18to0.82eV at 400K. The dielectric transition is explained as the change of the crystal field caused by the thermal expansion or by the surface bond contraction in the small CrO2∕Ag particles. At 300K, the nanocomposite has an increased coercivity of 650Oe, with a saturation magnetization of 75emu∕g (equivalent to 1.13μB per Cr4+ ion), which is attributed to the spin pinning in the single domain CrO2∕Ag particles.