Thermal and magnetic studies of nanocrystalline Ni

Ultra-fine Ni particles with average particle sizes from 12 to 100 nm were prepared by the evaporation technique. The calorimetric effects of nanocrystalline Ni as well as the NiO and Ni bulk samples were measured between 300 and 800 K. Both an exothermal effect between 380 and 480 K and an endothermal peak near 560 K were observed for ultrafine Ni; only endothermal peak was observed for both NiO near 520 K and bulk Ni near 630 K. A shifted magnetic hysteresis loop and a slope change in saturation magnetization were observed below roughly 50 K for ultra-fine Ni particles with average particle sizes roughly below 50 nm. This is explained by the effect of exchange anisotropy interaction between the interfaces of the ferromagnetic region and the layers of antiferromagnetic NiO on the surface of the nanocrystalline Ni particles.