Magnetic properties of nanocrystalline Cr 2O 3 synthesized in a microwave plasma

Abstract

Nanocrystalline Cr 2O 3 particles were synthesized in a microwave plasma using chromium hexacarbonyl as precursor. Electron microscopy revealed 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 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 found to be single crystals. The smaller particle fraction showed a granular substructure, resembling to a polycrystalline particle. The size 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 rhombohedral corundum structure. In the temperature range from 10 to 300 K the magnetic behavior can be described by a modified Langevin function but with a magnetic moment having a thermally activated component. In any event, in this temperature range the assumption Kv ⪡ kT is valid, where K is the anisotropy energy and v the particle volume. The thermally activated magnetization can be attributed to the material with the granular substructure. The size of the magnetic domains was found to be identical with the electronmicroscopically determined size of the granules.