Formation of magnetic Ni nanoparticles in x-ray irradiated electroless solution

Magnetic nanostructures are attracting tremendous interest as regards application in high-density data storage devices and magnetic fluids. We have prepared magnetic nanoparticles (similar to7.5 nm) by x-ray irradiation of electroless solutions and furthermore have investigated their structural and magnetic properties. Interestingly, we find that the formation of these Ni nanoparticles occurs spontaneously, during the room temperature process, dominantly at electrolyte pH of 8.2. The hydrated electrons produced during the irradiation of electroless solution seem to play a decisive role in the spontaneous formation and growth of nanoparticles. The possible surface alloying and/or coating over these pure Ni cores occurs only upon longer irradiation of high-P-content solutions. This suggests a possible catalytic behaviour of these nano-Ni surfaces in relation to P counter-ions in the irradiated solutions. The magnetic properties of these 'as-received' particles have been studied using a vibrating sample magnetometer. The saturation magnetic moment per gram for the Ni particles is 9.38 emu g(-1), which is 17% of the saturation moment of bulk ferromagnetic Ni at room temperature; this can be attributed due to the size effect of these magnetic domains. The symmetric hysteresis loop about the zero-field axis showing negligible loop shift (DeltaH(c) similar to 3-10 Oe) suggests that Ni particles are free from oxide layers.