THEORETICAL STUDY IN NANO-PHYSICS OF MAGNETIC ATOM BRIDGES CONTROLLED BY THE STM TIP MANIPULATIONS - NANO-STRUCTURE, NANO-MAGNETISM

利用基于密度泛函理论的第一性原理计算，研究了扫描隧道显微镜（STM）尖端与固体表面之间的磁性原子桥的纳米物理：纳米晶格结构、纳米磁性和量子输运。我们利用线性链结构的简单结构的铁原子桥，展示了stm尖端操纵引起的磁态变化的起源，以及磁态变化如何影响电子传递现象。总能量计算结果表明，线性链结构的铁原子桥不稳定，其晶格太弱，无法显示磁态的变化。稳定的原子桥为之字形链结构，其磁态始终为高自旋铁磁态。我们寻找晶格结构足够强，能表现出磁态变化的原子桥的稳定结构。我们找到了这样一个稳定的…结构。这就是扭曲的阶梯结构。具有扭曲阶梯结构的铁原子桥足够稳定，可以通过压缩长度来经历其磁性状态的变化。我们证明了通过stm尖端操作来控制磁态是可能的。我们还研究了磁性合金原子桥的磁性能。在Fe_<1-x>Ni_x合金原子桥的情况下，我们发现原子保持相当大的磁矩（Fe原子约为3μB， Ni原子约为0.9μB），并且原子桥中每个原子的平均磁矩随x的增加而线性减小。除了x=1.0外，Fe_xV_<1-x>合金的原子桥与Fe_<1-x>的Ni_x合金的原子桥表现出强烈的对比，并与相应合金的大部分相似。在Fe_<1-x>V_x合金原子桥中，V原子没有磁矩，而Fe原子的磁矩比体铁晶体中的磁矩小。Fe- v原子混合使Fe- v合金原子桥中Fe原子的磁矩显著降低。这些结果给了我们原子桥版本的鲍林-斯莱特曲线。此外，我们还测定了通过这些原子桥的自旋输运现象。我们认为这样的系统研究为原子桥相关的纳米自旋电子器件的设计和制造奠定了基础。少

We investigated the nano-physics : nano-lattice-structure, nano-magnetism, and quantum transport, of the magnetic atom bridges constructed between a tip of a scanning tunneling microscope (STM) and a solid surface with the aid of first-principles calculation based on the density functional theory.We show the origin of a change in the magnetic state induced by the STM-tip manipulation and how the change in the magnetic state affects the electron transport phenomena by use of the Fe atom bridge of the simple structure, the linear chain structure. As a result of total energy calculation, the Fe atom bridge of the linear chain structure is unstable and its lattice is too weak to show the change in the magnetic state. The stable atom bridge is of the zigzag chain structure, whose magnetic state is always high-spin ferromagnetic stateWe searched the stable structure of the atom bridge whose lattice structure is enough strong to show a change in the magnetic state. We have found such a stable … More structure. That is the twisted ladder structure. The Fe atom bridge with a twisted ladder structure is stable enough to undergo changes in its magnetic state via compression in length. We showed that it is possible to control the magnetic state by the STM-tip manipulations.We have also investigated the magnetic properties of magnetic alloy atom bridges. In the case of an Fe_<1-x>Ni_x alloy atom bridge, we have found that the atoms maintain a considerably large magnetic moment (about 3μB for an Fe atom and about 0.9μB for a Ni atom), and that the mean magnetic moment per atom in the atom bridge decreases linearly as x increases. In the case of an Fe_xV_<1-x> alloy atom bridges shows a strong contrast with that of the Fe_<1-x>Ni_x alloy atom bridges, and similarities with the bulk of the corresponding alloy, except for the case of x=1.0. In the Fe_<1-x>V_x alloy atom bridge, a V atom has no magnetic moment, and an Fe atom has a smaller magnetic moment than that in the bulk Fe crystal. The magnetic moment of the Fe atom in the Fe-V alloy atom bridge is strongly reduced by the Fe-V atom mixing. These results give us the atom bridge version of the Pauling-Slater curve.Furthermore, we have determined the spin transport phenomena trough these atom bridges. We think that such a systematic investigation gives us the important and useful information in order to establish a basis for the design and fabrication of the atom bridge related nano-spin-electronics devices. Less