Ishizaki Toshitaka, Yatsugi Kenichi, Akedo Kunio
Toyota Central R&D Labs., Inc., 41-1 Nagakute, Aichi 480-1192, Japan.
Nanomaterials (Basel). 2016 Sep 13;6(9):172. doi: 10.3390/nano6090172.
Magnetic cores of passive components are required to have low hysteresis loss, which is dependent on the coercive force. Since it is well known that the coercive force becomes zero at the superparamagnetic regime below a certain critical size, we attempted to synthesize Ni nanoparticles in a size-controlled fashion and investigated the effect of particle size on the magnetic properties. Ni nanoparticles were synthesized by the reduction of Ni acetylacetonate in oleylamine at 220 °C with trioctylphosphine (TOP) as the capping agent. An increase in the TOP/Ni ratio resulted in the size decrease. We succeeded in synthesizing superparamagnetic Ni nanoparticles with almost zero coercive force at particle size below 20 nm by the TOP/Ni ratio of 0.8. However, the saturation magnetization values became smaller with decrease in the size. The saturation magnetizations of the Ni nanoparticles without capping layers were calculated based on the assumption that the interior atoms of the nanoparticles were magnetic, whereas the surface-oxidized atoms were non-magnetic. The measured and calculated saturation magnetization values decreased in approximately the same fashion as the TOP/Ni ratio increased, indicating that the decrease could be mainly attributed to increases in the amounts of capping layer and oxidized surface atoms.
无源元件的磁芯需要具有低磁滞损耗，而磁滞损耗取决于矫顽力。由于众所周知，在低于一定临界尺寸的超顺磁状态下矫顽力变为零，我们尝试以尺寸可控的方式合成镍纳米颗粒，并研究粒径对磁性能的影响。通过在220℃下用三辛基膦（TOP）作为封端剂在油胺中还原乙酰丙酮镍来合成镍纳米颗粒。TOP/Ni比的增加导致粒径减小。通过0.8的TOP/Ni比，我们成功合成了粒径低于20nm且矫顽力几乎为零的超顺磁性镍纳米颗粒。然而，饱和磁化强度值随着粒径减小而变小。基于纳米颗粒内部原子是磁性的而表面氧化原子是非磁性的假设，计算了没有封端层的镍纳米颗粒的饱和磁化强度。随着TOP/Ni比增加，测量和计算的饱和磁化强度值以大致相同的方式降低，表明这种降低主要可归因于封端层和氧化表面原子数量的增加。
