Research on Tunneling Spectroscopy and Magnetism of Multilayered Films

本研究的目的是通过自旋相关的隧道效应，对多层膜的电子态和磁性有一个基本的了解。结果表明：[1]在3~300K的温度范围内，在高达15kOe的磁场中，结的隧穿特性可以得到改善。由于目前的资助，系统中已经引入了低温温度计/控制器(棕榈滩低温物理学，型号4075型)。[2]结的制备和自旋相关隧道谱研究了以下类型的结。(1)Al(或Fm)/Al_2O_3/Fm结(Fm：Ni或Co)(2)Al(或Fm)/Al_2O_3/Al/Fm结(3)Fm/NiO/Ni结在制备(I)和(2)结时，首先在玻璃衬底上沉积一个Fm电极。然后在第一个电极上沉积了一层非常薄的铝膜。它的表面被氧化形成Al_2O_3的隧道势垒，最后在其上蒸发一个对电极。这种方法是我们自己发明的，具有选择第一电极的灵活性和Al_2O_3势垒的稳定性的优点。虽然上述的最终目标还没有达到，但已经进行了磁化曲线和铁磁共振等磁性测量以及隧道实验。[3]室温下磁阀效应的观察在检测(3)型结时，发现它们的隧穿电导依赖于FM和第一镍电极磁化的相对角度(磁阀效应)，即使在室温下也是如此。这种效应在理论上是可以预料到的，然而，在低温下只有少数实验结果被报道。

The purpose of this research is to acquire a basic understanding about the electronic state and magnetism of multilayered films, by means of spin-dependent tunneling. The results are as follows.[1] Improvement of experimental system Tunneling characteristics of junctions can be obtained at temperatures between 3 and 300K, and in magnetic field up to 15 kOe. A cryogenic thermometer/controller (Palm Beach Cryophsics; Model 4075) has been introduced into the system owing to the present grant.[2] Preparation of junctions and spin-dependent tunneling spectroscopy Those following types of junctions were examined. (1) AI(or FM)/Al_2O_3/FM junctions (FM: Ni or Co) (2) AI(or FM)/Al_2O_3/Al/FM junctions (3) FM/NiO/Ni junctions In preparing junctions of (i) and (2), a FM electrode was first deposited onto a glass substrate. A very thin Al film was then deposited over the first electrode. Its surface was oxidized to form a tunneling barrier of Al_2O_3. Finally, a counter electrode was evaporated across them. This method had been invented by us, and has advantages of flexibility in choosing the kind of the first electrode, and of the stability of Al_2O_3 barrier. Although the above mentioned final goal has not been reached yet, magnetic measurements such as magnetization curve and FMR were performed as well as tunneling experiments. The obtained results assure the future developments towards the goal.[3] The observation of magnetic valve effect at room temperature In examining junctions of type(3), it was found that their tunneling conductance depends on the relative angle between the magnetizations of the FM and the first Ni electrode (magnetic valve effect), even at room temperature. This effect has been expected theoretically, however, only a few experimental results have been reported at low temperature.