| dc.description.abstract | Ni nanoparticles were fabricated by the thermal evaporation method. We control the distance among particles by pressing the loosely packed nanoparticle powder samples, and studying the influence of interparticle interaction on the magnetic characters of Ni nanoparticle.
The blocking temperature of the loosely packed Ni nanoparticle powder sample in applied magnetic field 200 Oe is 200 K, we observe that there is not hysteresis at temperature range 4 K to 300 K. And at applied magnetic field 0.15 T, there is an antiferromagnetic transition at 50 K. The interaction among nanoparticles increases when the compacting density increases. The temperature of antiferromagnetic transition also increases, and there is not hysteresis above the antiferromagnetic transition temperature. Hysteresis is observed below the transition temperature. It means interaction of particles is lager than thermal energy below the transition temperature. Beside, we also observe the hysteresis curve is not symmetry at zero field in compacted samples. When compacting density increases, shift of hysteresis is increases. Compacting density is 60 %, the shift is about 400 Oe. This shift may form by spin glass of surface effect of Ni nanoparticles. As applied magnetic field gets back to zero field, the direction of surface magnetic moment is ordered by original applied magnetic field direction. Ferromagnetic central part of nickel nanoparticles can experience these come from surface magnetic moment effect, and make the hysteresis shift. The shift increases as compacting density increases, it means that surface spin glass layer become heavy as the pressure increases, and saturation magnetism of each different pressure reduces as the pressure increases. While compacting density is 60 %, the saturation magnetism of sample only 50 % of bulk left. | en_US |