Abstract: Fe₃O₄ is considered to be half metal nature and has a comparatively high Curie temperature of 858 K compared with other metal oxides, which makes it more attractive in spin, electronic application. The extrinsic magnetoresistance of Fe₃O₄ has been studied extensively, however, so far few progress is acheieved. Here, a new way is given to obtain higher MR. Fe₃O₄ nanospheres with the average diameter of about 200 nm is prepared and coated by SiO₂, which forms a shell of several nms. The nanopowder with SiO₂ shells, which serves as grain boundaries, is pressed and then sintered into compacts, which show enhanced MR. At different temperatures MR curves of compacts with SiO₂ and without SiO₂ differ much, and the former display a linear respond at high field range, which is interpreted as the existance of insulating SiO₂ grain boundaries.

Key words: magnetite nanoparticles, half metal, extrinsic magnetoresistance, spin, polarized tunneling

摘要： Fe₃O₄是一种半金属材料,在金属磁性氧化物当中有着较高的居里温度(858K), 因此在自旋电子应用当中有广阔的前景。通过在直径大约200 nm的单分散Fe₃O₄微球外包裹一层绝缘的SiO₂壳层而人工引入晶界,再冷压烧结成块状制成样品。与包膜前相比,样品的磁电阻效应大为增强,而且两者磁电阻的行为明显不同,后者在高场下出现一个线性关系,这是由SiO₂ 晶界引起的,相关的探索给出了一条新的提高磁电阻效应的途径。

关键词: Fe₃O₄纳米颗粒, 半金属, 非本征磁电阻效应, 自旋极化隧穿