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

1. Fe-SiO2颗粒膜磁化和磁阻的膜厚依赖性。饱和磁化强度随厚度的增加而增加，在200 nm左右，磁化强度和输运性质随厚度的变化呈现阶梯行为。这些行为可以用双层结构模型来解释；靠近衬底的第一层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是由一个模型来解释的，在这个模型中，在衬底附近非磁性壳的形成是增强的。这些结构经x射线光电子能谱证实。低维Co-SiO2薄膜的隧道磁电阻。(1)研究了超薄Co- sio_2颗粒膜的隧道巨磁电阻特性，形成Co颗粒的伪二维排列。在厚度为5 nm和10 nm的35 vol.%-Co薄膜中，磁阻（MR）比随着温度的降低而增加，与厚膜相似。另一方面，在28和32 vol.%-Co薄膜中，厚度小于5 nm，在100K以下，随着温度的降低，MR比急剧下降，这反映了Co颗粒的二维排列。(2)具有窄电流针孔的CPP（电流垂直于平面）结构样品AuCr/SiO_2/Co-SiO_2/SiO_2/AuCr的电流与电压（I-V）呈非线性关系，表明大多数或少数自旋带的隧穿势垒隧穿概率与e - 3的变化有关。交替沉积Co-Bi薄膜的磁性和输运特性。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Bi矩阵引起的OMR分量减小，而由Co引起的AMR分量增大。当x = 17时，自发霍尔电阻率表现出较强的温度依赖性。随着温度的升高，极性在150k时由负向正转换。在室温下，霍尔电阻率或霍尔系数比纯钴块体大2个数量级。Co注入GaAs杂化磁性半导体中的特殊霍尔效应。采用注入法制备了Co/GaAs杂化铁磁半导体材料。在这些样品中，薄片电阻表现出较弱的温度依赖性，并且观察到异常的正系数霍尔效应。在Co含量较低的样品中，霍尔电阻随温度的降低而增大，在150 K时达到最大值3.6 × 10-2 Ω。少

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