Abstrakt
We have studied magnetic properties of TCr2O4 (T = Co, Ni) ne powders, obtained by the citric acid method, and TCr2O4/SiO2 nanocomposites, constituted of spinel nanoparticles embedded in silica matrix fabricated by a modied sol gel method. All samples were characterized by powder X-ray diraction, scanning electron microscopy and microprobe analysis.
The prole analysis of the powder X-ray diraction revealed that the particle size is larger for the ne powder samples, as expected. Detailed measurements of magnetization, hysteresis loops and a.c. susceptibility demonstrate signicant dierences in magnetic properties of the ne powders in comparison to the nanocomposite samples.
The values of the coercitivity at 10 K ranges from 2T for NiCr2O4 ne powders to 0.6 T for CoCr2O4/SiO2 nanocomposites. Moreover, the hysteresis loops of the NiCr2O4/SiO2 samples are brightly asymmetric.
The phenomenon will be discussed in context of the exchange-bias originated by presence of a tiny amount of the antiferromagnetic phase, Cr2O3 in the samples.