原位研究掺杂Ni80Fe20薄膜的磁输运效应
Magnetotransport effects of ultrathin Ni80Fe20 films probed in-situ
摘要：
研究了在Al_2O_3、MgO和SiO_2衬底上生长的厚度从单层到12 nm的坡莫合金（Ni_（80）Fe_（20））薄膜的磁电阻特性。生长和输运的测量进行了低温条件下，在超高真空。应用面内磁矢量场高达100 mT，磁输运性能确定在生长过程中。随着厚度的增加，薄膜表现出从隧穿磁电阻到各向异性磁电阻的逐渐过渡。这对应于膜结构从分离的小岛到互连晶粒的网络的演变，以及膜的超顺磁性行为到铁磁性行为的转变。使用基于岛生长的理论模型的分析，我们发现，所观察到的演变的磁阻在隧道制度起源于岛的尺寸分布在生长过程中的变化。依赖于衬底材料，显着差异的磁阻响应之间的过渡制度的隧道磁电阻和各向异性magnetoresistance.We归因于一个越来越明显的岛的生长和坡莫合金的渗滤过程较慢时，比较生长在SiO2，MgO和Al2O3衬底。不同的生长特性导致SiO2的隧穿磁电阻和各向异性磁电阻的明显提前发生。特别是对于Al2O3的生长模式的结果在包含两个不同的贡献的铁磁性，导致两个不同的矫顽场在高厚度制度的膜的结构。
英文摘要：
We have investigated the magnetoresistance of Permalloy (Ni80Fe20) films with thicknesses ranging from a single monolayer to 12 nm, grown on Al2O3, MgO and SiO2 substrates. Growth and transport measurements were carried out under cryogenic conditions in UHV. Applying in-plane magnetic vector fields up to 100 mT, the magnetotransport properties are ascertained during growth. With increasing thickness the films exhibit a gradual transition from tunneling magnetoresistance to anisotropic magnetoresistance. This corresponds to the evolution of the film structure from separated small islands to a network of interconnected grains as well as the transition from superparamagnetic to ferromagnetic behavior of the film. Using an analysis based on a theoretical model of the island growth, we find that the observed evolution of the magnetoresistance in the tunneling regime originates from the changes in the island size distribution during growth. Depending on the substrate material, significant differences in the magnetoresistance response in the transition regime between tunneling magnetoresistance and anisotropic magnetoresistance were found. We attribute this to an increasingly pronounced island growth and slower percolation process of Permalloy when comparing growth on SiO2, MgO and Al2O3 substrates. The different growth characteristics result in a markedly earlier onset of both tunneling magnetoresistance and anisotropic magnetoresistance for SiO2. For Al2O3 in particular the growth mode results in a structure of the film containing two different contributions to the ferromagnetism which lead to two distinct coercive fields in the high thickness regime.
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