Fe-Al_2O_3颗粒膜的隧道巨磁电阻效应

TUNNELING GIANT MAGNETORESISTANCE IN Fe Al 2O 3 GRANULAR FILMS

对射频共溅射法制备的ＦｅＡｌ２Ｏ３颗粒膜的隧道巨磁电阻效应进行了研究．当Ｆｅ体积百分比为４５％时，样品的室温磁电阻的变化率（ＭＲ）在１Ｔ的平行膜面的磁场下可达４４％．磁测量表明在室温时样品呈超顺磁态．另外，从ＭＲ随温度的变化关系曲线可以看出，当温度低于５０Ｋ时，ＭＲ随着温度的下降而显著增加，ＭＲ在２０Ｋ时达到１４９％，４２Ｋ时可达２６％，大大超过理论的预期值，这可能与低温下由库仑抑制效应引起的自旋相关隧穿的高阶效应有关．

Abstract Tunneling giant magnetoresistance(TGMR) in Fe Al 2O 3 granular films which were prepared by co sputtering have been reported.MR ratio of the film with Fe volume fractions f V ≈0 45 takes a maximum of 4 4% at room temperature when a magnetic field of 1T was applied parallel to the film plane,accompanying huge specific electrical resistivities of the order of 10 5 μ Ω·cm.Field dependence of the MR is well described by the form proportional to the square of the magnetization of the film.Temperature dependence of the MR ratio of the film has also been investigated.The MR exhibits strong temperature dependence.The MR below 50K remarkably increases with decreasing temperature resulting in MR=14 9% and 26% at 20 and 4 2K,respectively.The anomalous increase of the MR at low temperature seems to arise from the successive onset of higher order processes of spin dependent tunneling between large granules through intervening small ones with strong Coulomb blockade.