【作者】 隋支垚；

【导师】 金迎九；

【作者基本信息】 延边大学 ， 理论物理， 2010， 硕士

【摘要】 自旋电子学是近年来发展起来的一门新型交叉学科,主要利用电子的自旋来传输和存储信息.在自旋电子学领域,半金属铁磁体因为能够极大的提高从铁磁体注入电子到半导体时的自旋极化率,因而受到了科学家的广泛关注.Full-Heusler合金Co2FeSi在目前为止所报道的众多半金属铁磁体材料中具有最高的磁矩和居里温度,而被认为是理想的自旋电子注入源之一本文利用全势线性缀加平面波方法(full-potential linearized augmented plane wave mothod, FLAPW),结合广义梯度近似(generalized gradient approximation,GGA)并考虑晶格点有效的库仑交换作用U,研究了Heusler合金Co2FeSi (001)表面的电子结构,磁性以及半金属特性.沿[001]方向考虑了两种可能的表面,即Co原子终止的表面与Fe和Si原子终止的表面.计算结果表明：(1)Co原子终止的表面将失去半金属特性.这是由于表面的产生导致表面层Co原子的配位数减少,其自旋向下的态密度发生局域化,并从低能级向高能级移动,破坏表面层Co原子自旋向下子带的带隙.表面层自旋极化率分别为-48.3%(U7.5)和-43.2%(U10).表面层Co原子的自旋磁矩(～1.75μB)与中间上一层Co原子的自旋磁矩(～1.51μB)相比有了明显增加,是因为表面层Co原子的配位数减少,使表面层Co原子的交换劈裂有所增加.表面下一层Fe原子的自旋磁矩(～3μB,)与中间层Fe原子的自旋磁矩(～3.15μB,)相比有所减小,这是由于表面下一层Fe原子与表面层Co原子杂化增强所致.(2)Fe和Si原子终止的表面也失去了半金属特性.这是由于表面的产生使表面层Fe原子的最近邻Co原子的数目由原来的八个减少至四个,因此未填充的自旋向下的态由高能级向低能级移动,同时能隙出现了表面态.表面层自旋极化率分别为-87.3%(U7.5)和-43.2%(U10).表面层Fe原子的自旋磁矩(～3.28μB)大于中间层自旋磁矩(～3.14μB),是因为表面层Fe原子的配位数减少使表面层Fe原子的交换劈裂有所增加.表面下一层和中间上一层的Co原子的自旋磁矩基本上没有变化.更多还原

【Abstract】 Spintronics is a new interactive-type subject in recent years; it mainly explores the transport and storage of information by electron spin. In spintronics, the Half-metallic alloy attracts great attentions, because it could improve electron spin polarization when the alloy injects into the semiconductor. In present, the Full-Heusler alloy Co2FeSi has the highest magnetic moment and Curie temperature in the reported many ferromagnet materials. It is considered an ideal source of spin injection.In this paper, by the full-potential linearized augmented plane wave (FLAPW) method within the generalized gradient approximation (GGA) and plus on-site coulo-mb exchange interaction U, we have investigated the electronic structures, magnetism and half-metallicity of the Full-Heusler alloy Co2FeSi (001) surface. For [001] directi-on, we have considered two types of surfaces:the Co atoms terminated and the Fe and Si atoms terminated surfaces. The results are followings:(1) Co atoms terminate surface will loss the half-metallicity. It was found that the minority-spin states of Co (surface) atoms were localized and moved to higher energy from lower energy, which destroys the minority spin band gap due to the reduced coordination number of Co (surface) atoms. The calculated spin polarizations of the surface layer are negative with values of-48.3%(U75) and-43.2%(U10). The magnetic moment (～1.75μB) of the surface Co atom is larger than that (～1.51μB) of the inner layer because of the reduced coordination number of Co (surface) atom, which increases the exchange splitting at the surface. The magnetic moment (～3μB) of the subsurface Fe atom decreased slightly than that (～3.15μB) of the center layer due to increased covalent hybridization between the Fe (subsurface) and the Co (surface) atoms.(2) Fe and Si atoms terminated surface also loss the half-metallicity. At the surface the coordination number of Fe (surface) atoms was reduced from 8 to 4 Co atoms. It was found that the unoccupied minority-spin states of surface Fe atoms shifted from higher energy to lower energy, and the surface states appear in the band gap. The calculated spin polarizations for the surface layers are negative with values of-87.3%(U7.5) and-43.2%(U10). The magnetic moment (～3.28μB) of surface Fe is slightly larger than the value (～3.14μB) of the inner layer due to the increase of the exchange splitting at the surface. On the other hand, the magnetic moment of subsurface Co atom is similar to that of the inner layer Co atom.更多还原