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 o f nanocrystalline Ni as well as the NiO and Ni bulk samples were measu red between 300 and 800 K. Both an exothermal effect between 380 and 4 80 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 i n saturation magnetization were observed below roughly 50 K for ultra- fine Ni particles with average particle sizes roughly below 50 nm. Thi s is explained by the effect of exchange anisotropy interaction betwee n the interfaces of the ferromagnetic region and the layers of antifer romagnetic NiO on the surface of the nanocrystalline Ni particles.