Impedance spectra of field-aligned CrO2 needle-shape powders

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.

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NEAR STATIONARY DIELECTRIC PROPERTIES IN HALF-METALLIC FERROMAGNETIC Ag:CrO₂ NANOCOMPOSITE PARTICLES AT HIGH FREQUENCIES

Singh

Ram

Thakur

2008

Mod. Phys. Lett. B

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Nanocomposite particles of silver modified CrO 2 were synthesized by a chemical CrO 3 → CrO 2 reduction in the presence of Ag + in an aqueous medium whereby the half-metallic ferromagnetic particles of CrO 2 are generated within a shell of silver. The dielectric constant εr, AC resistivity ρAC, and the dielectric power loss were studied after annealing recovered Ag:CrO 2 powder (compacted as the billets), at 300°C for 2 h in air, at 10–1000 kHz frequencies (f) at room temperature. At 10 kHz, the ρr has as large a value as 49, with ρ AC = 106 k Ω-cm and power loss 0.42. As f increases, all the three parameters are decreased monotonically to the values 28, 3.6 kΩ-cm, and 0.06 respectively. Almost a steady εr as well as ρAC value exists, with controlled power loss, useful for high frequency applications over f ≥ 400 kHz .

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Impedance spectra of field-aligned CrO2 needle-shape powders

Cited by 3 publications

References 16 publications

Advanced Ceramics and Nanocomposites of Half-metallic Ferromagnetic CrO2 for Magnetic, GMR and Optical Sensors

Advanced Ceramics and Nanocomposites of Half-metallic Ferromagnetic CrO2 for Magnetic, GMR and Optical Sensors

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

NEAR STATIONARY DIELECTRIC PROPERTIES IN HALF-METALLIC FERROMAGNETIC Ag:CrO₂ NANOCOMPOSITE PARTICLES AT HIGH FREQUENCIES

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Impedance spectra of field-aligned CrO2 needle-shape powders

Cited by 3 publications

References 16 publications

Advanced Ceramics and Nanocomposites of Half-metallic Ferromagnetic CrO2 for Magnetic, GMR and Optical Sensors

Advanced Ceramics and Nanocomposites of Half-metallic Ferromagnetic CrO2 for Magnetic, GMR and Optical Sensors

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

NEAR STATIONARY DIELECTRIC PROPERTIES IN HALF-METALLIC FERROMAGNETIC Ag:CrO2 NANOCOMPOSITE PARTICLES AT HIGH FREQUENCIES

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NEAR STATIONARY DIELECTRIC PROPERTIES IN HALF-METALLIC FERROMAGNETIC Ag:CrO₂ NANOCOMPOSITE PARTICLES AT HIGH FREQUENCIES