覆盖层对磁性隧道结中隧道磁电阻的影响
Large influence of capping layers on tunnel magnetoresistance in magnetic tunnel junctions
摘要：
实验中发现，覆盖层对隧道磁电阻效应有很大的影响，它可以增强磁隧道结的垂直磁各向异性。为了探索覆盖层对TMR的影响，我们对X（001）中的TMR进行了从头计算|CoFe（001）|氧化镁（001）|CoFe（001）|X（001）MTJ，其中X表示可为钨、钽或铪的覆盖层材料。我们报告TMR在不同的MTJ和证明，钨是一个理想的候选人一个巨大的TMR比。给出了布里渊区的透射谱。可以看出，在MTJ的平行条件下，尖锐的透射峰出现在少数自旋沟道中。这一现象归因于共振隧道传输效应，我们解释了它的层分辨态密度（DOS）。为了研究MTJ的输运性质，从能带对称性的角度研究了MTJ的散射态密度。已经发现CoFe|在反平行条件下，钨界面阻挡了散射态的传输。本文研究了不同覆盖层的MTJ的TMR和输运特性，证明了钨是一种合适的覆盖层材料，这将有助于MTJ的设计和优化。
英文摘要：
It has been reported in experiments that capping layers which enhance the perpendicular magnetic anisotropy (PMA) of magnetic tunnel junctions (MTJs) induce great impact on the tunnel magnetoresistance (TMR). To explore the essential influence caused by capping layers, we carry out ab initio calculations on TMR in the X(001)|CoFe(001)|MgO(001)|CoFe(001)|X(001) MTJ, where X represents the capping layer material which can be tungsten, tantalum or hafnium. We report TMR in different MTJs and demonstrate that tungsten is an ideal candidate for a giant TMR ratio. The transmission spectrum in Brillouin zone is presented. It can be seen that in the parallel condition of MTJ, sharp transmission peaks appear in the minority-spin channel. This phenomenon is attributed to the resonant tunnel transmission effect and we explained it by the layer-resolved density of states (DOS). In order to explore transport properties in MTJs, the density of scattering states (DOSS) was studied from the point of band symmetry. It has been found that CoFe|tungsten interface blocks scattering states transmission in the anti-parallel condition. This work reports TMR and transport properties in MTJs with different capping layers, and proves that tungsten is a proper capping layer material, which would benefit the design and optimization of MTJs.
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