Impedance and magnetic properties of chemically synthesized CrO2/Ag nanocomposite particles.

The impedance of CrO2/Ag nanocomposite particles has been investigated in the frequency range of 100 Hz–1 MHz at a temperature of 300–475 K. The impedance in the form of Cole-Cole plot reveals that the resistivity contribution primarily comes from bulk grain interior below 375 K and above those from both the grain interior and grain boundaries. The grain interior resistance decreases from 163 kΩ at 300 K to 6 kΩ at 475 K with a typical semiconductor like behavior. Above 375 K, 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 0.18 to 0.82 eV at 400 K. 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 300 K, the nanocomposite has an increased coercivity of 650 Oe, with a saturation magnetization of 75 emu/g (equivalent to 1.13μB per Cr4+ ion), which is attributed to the spin pinning in the single domain CrO2/Ag particles. [ABSTRACT FROM AUTHOR]