Ferromagnetic ordering at room temperature in ZnO:Co nanoparticles

Intrinsic room temperature ferromagnetisin is reported in sequentially sintered (in air ambient) nanocrystalline ZnO:Co (1 to 10 at% Co) samples prepared by chemical route. The Curie temperature of the ZnO:Co ferromagnetic samples is determined to be similar to 495 degrees C. The saturation magnetization of the ferromagnetic phase is found to first increase with Co concentration (up to 5%) and then decrease. It is also found to decrease with increase in sintering temperature Lip to 800 degrees C; there after it remains unaffected till 1000 degrees'C. The d-d band transitions in the optical spectrum confirm that Co2+ substitutes Zn2+ in the ZnO lattice. A plausible explanation of the observed ferromagnetic ordering is presented in terms of Bound Magnetic Polarons model.