Study on the Tunneling Effect into Amorphous Magnetic Alloys

自旋方向的依赖性是决定被薄绝缘体层隔开的两种金属之间隧穿电流的一个有趣因素。本研究项目的目的是利用自旋极化隧道能谱法对磁性合金，特别是非晶磁性合金的磁性能有基本的认识。在自旋极化隧道能谱法中，超导铝电极的能隙处的锋利边缘通常被用作“探针”来研究对电极中的自旋极化能态。在温度为1 ~ 300 K、磁场小于15 kOe的条件下，测量了隧道结的电流与外加电压曲线（I-V）。电子系统采用了锁相放大器，实现了di/dV特性的测量。在所研究的磁性金属电极上真空蒸发一层厚度大于50 A的薄铝，然后在空气中氧化形成Al_2O_3的隧道势垒，最后在其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玻璃基板/磁性金属/Al_2O_3/已知电子态金属，不同于通常的Al/Al_2O_3/磁性金属结构。由于极薄的Al_<23>层在磁性金属薄膜的形成过程中没有被破坏，因此该结构使电子隧穿进入各种金属的研究成为可能。研究了空气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。将自旋极化隧道效应的应用扩展到非晶合金薄膜的磁性研究中，对非晶合金薄膜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.