Study on New Magnetic Nanoparticles

研究了过渡金属氧化物纳米颗粒的磁性。关于Ni(OH)2单层纳米团簇(Ni-MNC)的磁化强度测量已有报道，此外，为了证实其二维局域结构，用XAFS分析了其局部结构。在磁化强度测量中，虽然NiO大块晶体表现出反铁磁性，但仍观察到了超顺磁性或铁磁行为。Fe-O体系中存在Y-Fe_2O_3和α-Fe_2O_3纳米粒子，这取决于热处理温度和时间。在1023K热处理10h的样品具有较大的压制力，约为1Koe。这种材料有望实现高密度磁记录介质。这一结果发表在2001年的《日刊新闻》上。为了改善纳米Fe_2O_3的磁参数，将Co离子掺杂到纳米氧化铁颗粒中。Co/Fe的摩尔比在0.05~0.7之间变化。在100K测量温度下，随着Co离子加入量的增加，材料的结晶性开始急剧增加，但在Co/Fe比为0.4附近观察到最大的结晶性后，没有发现更大的结晶性，在较高的浓度下反而降低。

Magnetic properties of transition metal-oxide nanoparticles were investigated. Magnetization measurements were already reported for Ni(OH)2 monolayer nanoclusters (Ni-MNC), and additionally, in order to confirm their two dimensionality local structure was studied by XAFS analyzes.NiO nanoparticles were produced by annealing above mentioned Ni(OH)2. Their diameters were estimated between 2 and 6 nm. In the magnetization measurements superparamagnetic or ferromagnetic behaviors were observed though NiO bulk crystal shows antiferromagnetism.y-Fe203 and α-Fe2O3 nanoparticles were confirmed for Fe-O systems depending on annealing temperature and annealing time. Large coersive force of about 1 kOe was found for the sample annealed at 1023 K for 10 hours. This material could be expected to realize high density magnetic recording media. This result was reported by Nikkan Kogyo Newspaper in 2001.In order to improve mangnetic parameters of Fe2O3 nanoparticles, Co ions were doped into iron oxide nanopartcles. Mole ratio of Co/Fe was varied between 0.05 and 0.7. Under the measuring temperature of 100 K, coersivity began to increase drastically as the amount of Co ion increased, however, after the largest coersivity was observed near 0.4 of Co/Fe ratio, no larger coersivity could be found and it rather decreased in higher concentration.