Agx(Fe3O4)1-x (x = 0, 0.1, 0.2 and 0.3) composite thin films consisting of a ferrimagnetic spinel Fe3O4 phase and a non-magnetic metal Ag phase were prepared by sol-gel method in combination with spin-coating technique. The microstructure observation of the thin films by magnetic force microscope indicated that the Fe3O4 grains are nearly spherical with a diameter ranging from 75 nm to 85 nm which is less than the theoretically calculated critical diameter of single-domain Fe3O4 particles. The coercivity of the films is about 23.1 kA/m for the thin film with x=0.1 and 28.6 kA/m for that with x = 0.3 respectively, which are nearly equal to the magnetocrystalline anisotropy field HK of Fe3O4 (namely 27.1 kA/m). At room temperature (300 K), the thin film with x = 0.1 has a maximal magnetoresistance of-3.5% under a magnetic field of 700 kA/m, which is higher than that (-2.2%) of a pure Fe3O4 film. The magnetoresistance is decreased with further increasing Ag content. Therefore, an appropriate addition of Ag is favorable for the enhancement of the room-temperature magnetoresistance of Fe3O4 thin film, which can be attributed to the combined effect of the spin-dependent scattering at the interfaces between Fe3O4 grains and Ag granules as well as the spin-polarized tunneling at boundaries between Fe3O4 grains of spin-polarized electrons.%采用溶胶-凝胶技术结合旋涂法,以聚乙烯醇作为鳌合剂,选择适当的退火程序,制备了由金属Ag相和Fe3O4相所组成的Agx(Fe3O4)1-x=0,0.1,0.2,0.3)复合薄膜.磁力显微镜观察表明,Fe3O4晶粒为单畴颗粒,其直径为75～85 nm,小于理论计算的单畴,临界尺寸.磁性测量表明:x=0.1和0.3薄膜的矫顽力坼分别为23.1 kA/m和28.6 kA/m,很接近于Fe3O4的磁晶各向异性场HK(27.1 KA/m).室温(300K)下,x=0.1的薄膜具有最大的磁电阻,700 kA/m磁场下为-3.5%,高于纯Fe3O4薄膜的低场磁电阻(-2.2%).随着Ag含量进一步增加,薄膜的室温磁电阻减小.适量金属Ag的掺入有利于提高Fe3O4薄膜的磁电阻,这归因于自旋极化电子在Fe3O4晶粒和Ag颗粒界面处的自旋相关散射以及穿过Fe3O4-Fe3P4晶界的自旋极化隧穿的共同作用.
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