Research on Tunneling Spectroscopy and Magnetism of Multilayered Films

本研究的目的是利用自旋相关的隧道效应，对多层薄膜的电子态和磁性有一个基本的认识。结果如下实验系统在3 ~ 300K的温度和15 kOe的磁场下均可获得结的隧穿特性。低温温度计/控制器（棕榈滩低温物理；型号4075）已被引入到系统中，由于目前的拨款结的制备和自旋相关隧道光谱研究了以下几种结。(1) AI（或FM）/Al_2O_3/FM结（FM: Ni或Co） (2) AI（或FM）/Al_2O_3/Al/FM结(3)FM/NiO/Ni结在制备(i)和(2)结时，首先将FM电极沉积在玻璃基板上。然后在第一个电极上沉积了一层非常薄的铝膜。其表面被氧化形成Al_2O_3的隧道障壁。最后，在它们之间蒸发一个对电极。该方法具有第一电极选择灵活和Al_2O_3势垒稳定性好等优点。虽然上述最终目标尚未实现，但我们进行了磁化曲线、FMR等磁性测量以及隧道实验。取得的成果为今后朝着目标的方向发展提供了保证在对(3)型结的研究中发现，即使在室温下，它们的隧穿电导率也取决于FM与第一Ni电极磁化的相对角度（磁阀效应）。这种效应在理论上是可以预料到的，但在低温下的实验结果却很少。

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.