论文部分内容阅读
用气体蒸发法制备粒径在100—800A之间的铁、钴、镍金属超微粒。超微粒的生长机制与气压相关,在低气压下(P<3Torr)为成核生长;在高气压下(P>3Torr)为凝聚生长。电子显微镜观察到铁的非晶态超微粒。X射线衍射表明:铁、镍超微粒的晶格结构与相应的块物质相同,但钴超微粒有所不同,粒度为200—300A的钴为fcc结构。室温下,铁、钴、镍超微粒最高矫顽力分别为1000,1500和450Oe,对应的平均粒度为210,200和320A,其数值与理论计算的单畴颗粒尺寸大致相同。其饱和磁化强度随粒度的减小而单调减小。实验表明,超微粒的磁化强度减小与颗粒表面氧化层和一部分超顺磁性颗粒有关。表层氧化层原子的自旋磁矩与体内原子的目旋磁矩成一角度排列。低温下,铁磁超微粒的矫顽力很高,如300A铁为1350Oe,290A钴为2204Oe,270A镍为1050Oe。
Iron, cobalt, nickel metal ultrafine particles with a particle size of 100-800A are prepared by gas evaporation method. The growth mechanism of ultrafine particles is related to air pressure, nucleation growth at low pressure (P <3 Torr), and condensation growth at high pressure (P> 3 Torr). Electron microscopic observation of amorphous iron nanoparticles. X-ray diffraction shows that the lattice structure of the iron and nickel ultrafine particles is the same as that of the corresponding bulk material, but the cobalt ultrafine particles are different, and the cobalt having a particle size of 200-300 A has the fcc structure. At room temperature, the maximum coercivities of the iron, cobalt and nickel ultrafine particles are 1000, 1500 and 450 Oe, respectively. The corresponding average particle sizes are 210, 200 and 320 A, which are approximately the same as the theoretically calculated monodomain particle sizes. Its saturation magnetization monotonically decreases with decreasing grain size. Experiments show that the decrease of the magnetization of the ultrafine particles is related to the surface oxide layer and some superparamagnetic particles. The spin magnetic moment of the surface oxide layer atoms is arranged at an angle to the spin-on moment of the atoms in the body. At low temperatures, ferromagnetic ultrafine particles have a high coercive force, such as 300A iron 1350Oe, 290A cobalt 2204Oe, 270A nickel 1050Oe.