Tunneling magnetoresistance in Co-ZrO2 granular thin films
Tunneling magnetoresistance in Co-ZrO2 granular thin films
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DOI：
10.1103/physrevb.73.045418
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发表时间：
2006-01
影响因子：
3.7
通讯作者：
B. Hattink;M. G. D. Muro;Z. Konstantinović;X. Batlle;A. Labarta;M. Varela
中科院分区：
文献类型：
--
作者：
B. Hattink;M. G. D. Muro;Z. Konstantinović;X. Batlle;A. Labarta;M. Varela
采用脉冲激光沉积法在较宽的Co体积浓度范围内制备了纳米Co颗粒镶嵌在绝缘层中的颗粒膜。高分辨电子显微镜(TEM)显示，晶态颗粒与非晶态基质之间的界面非常清晰。通过对顺磁区域的低场磁化率和等温磁化强度与朗之万函数的分布进行拟合，由透射电子显微镜确定了窄的颗粒尺寸分布。随着Co体积浓度的增加，磁性颗粒尺寸变化不大，随着渗流极限的接近，磁性颗粒尺寸逐渐增大。利用井上-前川模型成功地再现了隧道磁阻。在5 0-2 1 30 0K内，TMR的最大值与温度无关，在低T$时，TMR的最大值显著增加，表明存在更高阶的隧穿过程.因此，清洁颗粒金属中的隧道电导和TMR由库仑带隙和固有的颗粒尺寸分布决定。
Granular films composed of well defined nanometric Co particles embedded in an insulating ${\mathrm{ZrO}}_{2}$ matrix were prepared by pulsed laser depositon in a wide range of Co volume concentrations $(0.15lxl0.43)$. High-resolution transmission electron microscopy (TEM) showed very sharp interfaces between the crystalline particles and the amorphous matrix. Narrow particle size distributions were determined from TEM and by fitting the low-field magnetic susceptibility and isothermal magnetization in the paramagnetic regime to a distribution of Langevin functions. The magnetic particle size varies little for Co volume concentrations $xl0.32$ and increases as the percolation limit is approached. The tunneling magnetoresistance (TMR) was successfully reproduced using the Inoue-Maekawa model. The maximum value of TMR was temperature-independent within 50\char21{}300 K, and largely increased at low $T$, suggesting the occurrence of higher-order tunneling processes. Consequently, the tunneling conductance and TMR in clean granular metals are dominated by the Coulomb gap and the inherent particle size distribution.