MAGNETIC-PROPERTIES OF NANOCRYSTALLINE CR2O3 SYNTHESIZED IN A MICROWAVE PLASMA

Nanocrystalline Cr2O3 particles were synthesized in a microwave plasma using chromium hexacarbonyl as precursor. Electron microscopy reveale d that the particle diameter is, depending on the process parameters, in the range from 7 to 9 nm or from 5 to 6 nm. In the case of the larg er particles, additionally elongated ones with a diameter from 6 to 7 nm and a length from 10 to 15 nm, were found, The larger particles wer e found to be single crystals. The smaller particle fraction showed a granular substructure, resembling to a polycrystalline particle. The s ize of these granules is in the range from 2 to 3 nm. The structure of the material was determined by electron diffraction to be the rhomboh edral corundum structure. In the temperature range from 10 to 300 K th e magnetic behavior can be described by a modified Langevin function b ut with a magnetic moment having a thermally activated component. In a ny event, in this temperature range the assumption K upsilon much less than kT is valid, where K is the anisotropy energy and upsilon, the p article volume. The thermally activated magnetization can be attribute d to the material with the granular substructure. The size of the magn etic domains was found to be identical with the electronmicroscopicall y determined size of the granules.