Study on the Tunneling Effect into Amorphous Magnetic Alloys

对自旋方向的依赖是一个有趣的因素，它决定了被一层薄的绝缘体隔开的两种金属之间的隧道电流。本研究的目的是利用自旋极化隧穿谱对磁性合金，特别是非晶态磁性合金的磁性有一个基本的了解。在该光谱中，超导铝电极能隙处的锐边通常被用作S“探头”，以研究超导铝电极中的自旋极化能态。在1K~300K的温度和小于15kOe的磁场下，测量了隧道结的电流-电压曲线。电子系统采用锁定放大器测量di/dv特性，将厚度大于50A的薄层Al真空蒸发到被研究的磁性金属电极上，然后在空气中氧化形成Al_2O_3隧道势垒，在该隧道势垒上真空蒸发已知电子态的对电极。本研究制备的隧道结结构为已知电子态的玻璃衬底/磁性金属/Al_2O_3/金属，这与通常的Al/Al_2O_3/磁性金属结构不同。由于在磁性金属膜的形成过程中，非常薄的Al_(23)&gt；层不会被破坏，因此这种结构使得研究电子隧穿到各种金属中成为可能。还研究了空气中氧化在镍电极上形成的NiO隧道势垒。研究了Ni/NiO/Ni和Ni/NiO/Co结的隧道效应，发现了一种新型的磁阻效应。自旋极化隧道效应的应用正在扩展到非晶态合金薄膜的磁性研究中，人们已经对其进行了各种磁性和结构测量。

Dependence on the spin directions is an interesting factor determining the tunneling current between the two metals seperated by a thin layer of insulator. The purpose of the present research project is to acquire the basic understanding of magnetic properties of magnetic alloys, especially of amorphous magnetic alloys, by means of the spin polarized tunneling spectroscopy, in which the sharpe edges at the energy gap of a superconducting Al electrode are usually used as s "probe" to investigate spin-polarized energy states in the conter electrode.The current versus applied voltage curves (I-V)curves of tunnel junctions were measured in temperatures between 1 K and 300 K, and in magnetic fields less than 15 kOe. The lock-in amplifier was adopted to the electronic system to enable measurements of di/dV characteristics.A thin layer of Al of more than 50 A thickness was vaccum evaporated onto a magnetic metal electrode under investigation, and was then oxidized in air to form a tunnel barrier of Al_2O_3, on which the counter electrode of known electronic state was finally vaccum evaporated. The structure of tunnel junctions prepared in the present study was Glass substrate/Magnetic metal/Al_2O_3/ Metal of the known electronic state, whic is different form the usual structure of Al/Al_2O_3/Magnetic metal. The present structure enables the investigation of lectron tunneling into various metals, since the very thin Al_<23> layer is not damaged during the formation of the magnetic metal films. NiO tunnel barrier formed on a Ni electrode by means of oxidation in air was also investigated. The tunnel effects of Ni/NiO/Ni and Ni/NiO/Co junctions were investigated, and a new type of magneto-resistance effect was found. The application of the spin polarized tunneling effect is being extended into the study of the magnetism of amorphous alloy films, whose various magnetic and structural measurements have been made.