Large tunnel magnetoresistance in magnetic tunnel junctions using Co2MnX (X = Al,Si) Heusler alloys
Large tunnel magnetoresistance in magnetic tunnel junctions using Co2MnX (X = Al,Si) Heusler alloys
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DOI：
10.1088/0022-3727/39/5/s09
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发表时间：
2006-03-07
影响因子：
3.4
通讯作者：
Miyazaki, T
中科院分区：
文献类型：
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作者：
Oogane, M;Sakuraba, Y;Miyazaki, T
通过优化各种制备条件（衬底、溅射靶的组成、衬底和后退火温度等），制备了b2有序co2mnnal和L2(1)有序Co2MnSi Heusler合金薄膜，并将这些薄膜应用于磁隧道结（MTJs）的底电极。我们在MTJs中使用了Al-氧化物绝缘隧道屏障，并改变了Al膜的氧化时间来控制Al-氧化物绝缘层和heusler合金/Al-氧化物界面的质量。所观察到的隧道磁阻（TMR）比对制备的Heusler合金薄膜的结构和表面形貌极为敏感。外延生长的Heusler合金薄膜显示出非常平坦的表面和提高的TMR比率。co2mnnal和Co2MnSi电极的MTJs具有良好的结构质量、TMR比对氧化时间的影响以及TMR比对测量温度的依赖关系。在具有无定形Al-oxide隧道势垒的MTJ中，外延生长b2有序Co2MnAl的MTJ在2k下获得的TMR比为83%。这一结果表明，b2有序Co2MnAl是一种高度自旋极化的材料，正如我们的理论计算所预测的那样。此外，我们观察到高质量外延生长的L2(1)有序Co2MnSi电极在MTJ中在2k下的TMR比达到159%。这是迄今为止使用无定形m -氧化物隧道势垒的MTJs的最高TMR值。由Julliere公式得到的Co2MnSi底电极的自旋极化约为0.89。这一数值也是迄今为止Heusler材料的最大数值，远远大于传统铁磁材料（如Co-Fe）的数值。这种大的自旋极化归因于半金属带结构，正如理论计算所预测的那样。
We fabricated B2-ordered Co2MnAl and L2(1)-ordered Co2MnSi Heusler alloy films by optimizing various fabrication conditions (substrate, composition of sputtering target, substrate and post-annealing temperature, etc) and applied these films to bottom electrodes of magnetic tunnel junctions (MTJs). We used Al-oxide insulating tunnel barriers for our MTJs and varied oxidation times of Al films to control qualities of the Al-oxide insulating layer and Heusler-alloy/Al-oxide interface. Observed tunnel magnetoresistance (TMR) ratios were extremely sensitive to the structure and surface morphology of the prepared Heusler alloy films. Epitaxially grown Heusler alloy films showed very flat surfaces and enhanced TMR ratios. The good structural quality, behaviour of the TMR ratios towards oxidation time for the preparation of the Al-oxide barriers and the measurement temperature dependence of the TMR ratios were quite different between the MTJs with Co2MnAl and Co2MnSi electrodes. The obtained TMR ratio of 83% at 2 K in the MTJ with epitaxially grown B2-ordered Co2MnAl was large among the MTJs with an amorphous Al-oxide tunnel barrier. This result suggests that B2-ordered Co2MnAl is a highly spin-polarized material, as predicted by our theoretical calculation. Moreover, we observed a very large TMR ratio of 159% at 2 K in the MTJ with a high-quality epitaxially grown L2(1)-ordered Co2MnSi electrode. This TMR ratio is the highest value to date in MTJs using an amorphous M-oxide tunnel barrier. Spin-polarization of the Co2MnSi bottom electrode obtained from Julliere's formula was about 0.89. This value is also the largest achieved to date for a Heusler material and is much larger than those of conventional ferromagnetic materials such as Co-Fe. This large spin-polarization is attributed to a half-metallic band structure, as predicted by theoretical calculations.