The influence of the shell on magnetic properties of CdS: Mn/SiO2 composite nanoparticles

Silica-coated Mn-doped CdS nanocrystals were synthesized by use of a reverse-micelle method. Transmission electron microscopy, X-ray diffraction and electron paramagnetic resonance were adopted to characterize the samples, and their magnetic properties were studied via superconducting quantum interference device magnetometry. The samples exhibit anomalous ferromagnetic property at low temperature. The CdS: Mn nanocrystals dispersed in a silica matrix exhibit an obvious hysteresis loop shift toward the direction of the magnetic field; by contrast, the nanocrystals coated with compact SiO2 shell layers display a symmetric hysteresis loop. The shell layers are supposed to be responsible for the distinct magnetic behaviors.