Magnetic properties of nanocrystalline Cr2O3 synthesized in a microwave plasma

Nanocrystalline Cr2O3 particles were synthesised using chromium hexacarbonyl as precursor. The particle diameter was, depending on the process parameters, in the range from 7 to 9 nm or from 5 to 6 nm. In the case of the larger 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 were single crystals. The smaller particle fraction showed a granular substructure, resembling a polycrystalline particle. The size of these granules was in the range from 2 to 3 nm. The material was of rhombohedral corundum structure. In the temperature range 10-300 K, the magnetic behaviour could be described by a modified Langevin function but with a magnetic moment having a thermally activated component. The thermally activated magnetisation could be attributed to the material with the granular substructure. The size of the magnetic domains was found to be identical to the size of the granules. 16 refs.