Controls of spin dependent tunneling in 2-dimensional granular magnetic films and development of active devices

1.Fe-SiO_2颗粒膜的磁化强度和磁阻随膜厚的变化规律：饱和磁化强度随膜厚的增加而增大，在200 nm附近出现阶跃行为，磁化强度和输运特性随厚度的变化而变化。这些行为可以用双层结构模型解释，第一层靠近衬底具有较小的磁化强度，第二层具有较大的磁化强度。这些磁性和输运性质可以用一个模型来解释，在该模型中，非磁性壳层的形成在衬底附近得到加强。这些结构经X-射线光电子能谱确证。(1)研究了Co-SiO_2超薄颗粒膜的隧穿巨磁电阻特性，形成了Co颗粒的准二维取向。在厚度为5 nm和10 nm的35vol.%-Co薄膜中，磁阻(MR)比随…的降低而增大更高的g温度类似于厚膜。另一方面，在厚度小于5 nm的28和32体积%-Co薄膜中，随着温度的降低，MR比在100K以下急剧下降，反映了Co颗粒的二维取向。(2)具有窄电流针孔的CPP(电流垂直于平面)结构的样品，AuCr/SiO_2/Co-SiO_2/SiO_2/AuCr，表现出电流-电压(I-V)关系的非线性，表明大多数或少数自旋带的隧道势垒隧穿几率与E.3的变化有关。交替沉积Co-Bi薄膜的磁性和输运性质。在Co-Bi薄膜中观察到普通磁阻(OMR)和各向异性磁阻(AMR)。随着Co体积分数x的增加，由铋基体引起的OMR组分减少，而由于Co的增加，AMR组分增加。当x=17时，自发霍尔电阻率表现出强烈的温度依赖性。随着温度的升高，极性在150K由负向正转变。在室温下，霍尔电阻率或霍尔系数比纯Co块体的霍尔系数大2个数量级。用离子注入的方法制备了Co/GaAs铁磁半导体。在这些样品中，方块电阻表现出微弱的温度依赖性，并且观察到了具有正系数的异常霍尔效应。在Co含量较小的样品中，霍尔电阻随温度的降低而增加，在150K以下时，霍尔电阻的最大值为3.6x10-2Ω。

1. Film thickness dependence of magnetization and magnetoresistance in Fe-SiO2 granular films.The saturation magnetization increases with thickness, and a step behavior appears at around 200 nm in the thickness dependence of the magnetization and transport properties. These behaviors are explained by a model of double-layered structure; the first layer near the substrate having smaller magnetization and the second layer with larger magnetization. These magnetic and transport properties is explained by a model, in which the formation of non-magnetic shell is enhanced near the substrates. These structure was confirmed by X-ray photoelectron spectroscopy.2. Tunneling magnetoresistance in low-dimensional Co-SiO2 films.(1) The tunneling giant magnetoresistance properties have been examined for ultrathin Co-SiO_2 granular films, forming the pseudo 2-dimensional alignment of Co granules. In the 35 vol.%-Co films of 5 and 10 nm thickness, the magnetoresistance (MR) ratio increased with reducin … More g temperature similar to thick films. On the other hand, in the 28 and 32 vol.%-Co films thinner than 5 nm, the MR ratio decreased drastically below 100K with reducing temperature reflecting the 2-dimensional alignment of Co granules.(2) Samples of CPP (current perpendicular to plane) structure with narrow current pin-holes, AuCr/SiO_2/Co-SiO_2/SiO_2/AuCr, exhibited the non-linearity in current to voltage (I-V) relation, suggesting that the tunneling barrier tunneling probabilities of majority or minority spin band relating to the variation of E.3. Magnetic and transport properties of alternately deposited Co-Bi films.Both ordinary magnetoresistance (OMR) and anisotropic magnetoresistance (AMR) are observed in Co-Bi films. The OMR component, for which the Bi matrix is responsible, decreases with increasing Co volume fraction x, while the AMR component, due to Co, increases. For x = 17, the spontaneous Hall resistivity indicates strong temperature dependence. With the increase of temperature, polarity switches at 150 K from negative to positive. At room temperature Hall Resistivity or Hall coefficient shows a larger value than pure Co bulk by 2 orders of magnitude.4. Extraordinary Hall effect in Co implanted GaAs hybrid magnetic semiconductors.Hybrid Co/GaAs ferromagnetic semiconductors have been prepared by implantation method. In these samples, sheet resistance shows weak temperature dependence, and the extraordinary Hall effect with positive coefficient is observed. In small Co content samples, Hall resistance increases with decreasing temperature and maximum value of 3.6 x 10-2 Ω is obtained at 150 K. Less