SYNTHESIS OF CrO₂ MODIFIED c-ZrO₂ OF FERROMAGNETIC NANOCOMPOSITE PARTICLES

Abstract

Ferromagnetic nanoparticles when dispersed in a dielectric ceramic matrix offer a new series of percolation composites with a metal-semiconductor or insulator interface that tailors the functional properties. In this purview, ZrO2 of a high dielectric constant (εr) is stabilized in a cubic (c) polymorph by incorporating CrO2 of strongly ferromagnetic nanoparticles. A selective composition 20 CrO2–80ZrO2 is synthesized after heating a polymer precursor with glycerol at 500°C–800°C in air for 2 h. Broadening of X-ray diffraction peaks reveals Cr4+:c-ZrO2 with an average crystallite size 5 nm in the 500°C heated sample and that is grown to 8 nm on increasing the temperature to 800°C. They occur as bundles of thin platelets in electron microscopic images. Both the samples have ferromagnetic hysteresis loops with 794 and 211 Oe of coercivities, respectively. Variations of εr-value and the power loss are studied as a function of frequency f (50 Hz–100 kHz range) on cold-pressed pellets at selective temperatures, in the 30°C–500°C range, in describing the effects of the magnetic species.

Influence of microstructure on the magnetic properties in Zr[sub 1-x]Cr[sub x]O[sub 2](x≤0.2) nanocrystallites

“…Transition metal cations like Mn 3+ , Fe 3+ /Fe 2+ , Co 2+ , Cr 3+ , or Cr 4+ have recently been explored to form a compound Zr 1-x M x O 2 on a partial M 2+ /M 3+ /M 4+ ĺ Zr 4+ substitution (M = transition metal) in a model dielectric host ZrO 2 [1][2][3]. The Zr 1-x M x O 2 is useful as a ferromagnetic semiconductor with a high Curie point for developing spintronics and magnetodielectrics.…”

“…A Cr 4+ ĺ Zr 4+ substitution is of great interest because the additive compound CrO 2 is well-known to exhibit a large saturation magnetization M s = 110 emu/g with nearly 100% spin polarization and excellent magnetotransport properties at room temperature [4,5]. A limited solubility of Cr 4+ in ZrO 2 and metastable nature of the +4 valence state of chromium in ambient air pressure, make it difficult to synthesize Zr 1-x Cr x O 2 by a conventional synthesis route [1,3]. Thus, Zr 1-…”