Silver-Modified CrO2 of Core–Shell Nanoparticles and their Magnetic and Impedance Properties
A chemical CrO3→CrO2 transformation reaction occurs in the presence of Ag+ species forming CrO2 core–shell magnetic nanoparticles. The process involves heating CrO3 with AgNO3 in an aqueous solution in ambient air at a low temperature of 330–350 K. Shell thickness (diamagnetic amorphous silver) is controlled to be ∼2 nm tunable to the magnetic and impedance properties. Improved coercivity Hc=75.7 mT and the Curie temperature TC=415 K are found with saturation magnetization Ms=80 Am2/kg after annealing the sample at 573 K in air for 2 h. On heating, the impedance (or electrical resistance) varies steadily through a maximum in the TC point in a typical half-metallic ceramic behavior. In a dynamic response to frequency f, the TC increases from 418 K at 1 kHz to as high a value as 505 K at 1 MHz. A nearly f independent and low value of dissipation factor as 0.05 is promising for low power loss high-frequency applications of such CrO2 particles.
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Document Type: Research Article
Affiliations: Materials Science Centre, Indian Institute of Technology, Kharagpur 721 302, India
Publication date: January 1, 2008