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Development of Spin-Tunneling Junctions with Large Magnetoresistance Using Half-Metallic Oxide Ferromagnets

使用半金属氧化物铁磁体开发具有大磁阻的自旋隧道结

基本信息

批准号：
11650320
负责人：
GOMI Manabu
金额：
$ 2.37万
依托单位：
Japan Advanced Institute of Science and Technology
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
1999
资助国家：
日本
起止时间：
1999 至 2000
项目状态：
已结题

项目摘要

Optimum fabrication conditions of the junctions and influence of surface magnetic of the ferromagnetic oxides on tunneling magnetoresistance have been investigated in order to achieve large magnetoresistance effect in tunneling junctions using transition metal oxides with half metallic nature. The results are summarized as follows :1.Thin films of Fe_3O_4 and MgO with high quality were grown by pulsed laser deposition (PLD) at low temperature. The insulating MgO layer was required to be grown at lower temperature than 200℃ even at oxigen pressure of 1 x 10^<-5> Torr in order to prevent the Fe_3O_4 surface from oxidizing in a fabrication process of junction. Thin films of Sr_2FeMoO_6 with half metallic nature which is a promising candidate of ferromagnetic electrode were successfully grown at 500℃, lower than the reported growth temperature.2.Optimum PLD-growth conditions for MgO insulating layers were determined. Analysis of current-voltage characteristics of Fe_3O_4/MgO/Au junction structures fabricated under the optimum conditions showed that the junctions with MgO insulating layer as thin as 1 nm have good tunneling quality.3.Tunneling magnetoresistane (TMR) due to the magnetization of the Fe_3O_4 electrodes aligned in anti-parallel was observed in a Co_<0.4>Fe_<2.6>O_4/Fe_3O_4/MgO/Fe_3O_4 junction, though the TMR change was as low as -0.5 %. The magnetic field dependence of TMR showed that the low TMR may be associated with the superparamagnetic behavior of the surface magnetization of Fe_3O_4 electrode layers.4.The Fe_3O_4/NiO/MgO/NiO/Fe_3O_4 junction structures with double insulating layers of non-magnetic MgO - magnetic NiO were fabricated. However, the expected junction properties were not obtained due to some issues caused by large junction area and NiO layers as thin as 1 nm. The advanced process fabricating the fine structure such as photolithography will be required to overcome these problems.

为了利用具有半金属性质的过渡金属氧化物在隧道结中实现大的磁电阻效应，研究了结的最佳制备条件以及铁磁氧化物表面磁性对隧道磁电阻的影响。主要研究结果如下：1.采用脉冲激光沉积法（PLD）在低温下生长了高质量的Fe_3O_4和MgO薄膜。为了防止在结的制作过程中Fe_3O_4表面被氧化，绝缘MgO层的生长温度必须低于200℃，即使在氧压为1 × 10 ~（-4）<-5>Torr的条件下也是如此。在低于文献报道的生长温度的500℃下成功地生长了具有半金属性质的Sr_2FeMoO_6薄膜，该薄膜是一种很有前途的铁磁电极候选材料。在最佳工艺条件下制备的Fe_3O_4/MgO/Au结结构的电流-电压特性分析表明，MgO绝缘层厚度为1 nm时，结具有良好的隧穿特性。3.在Co_ Fe_ O_4/Fe_3O_4/MgO/Fe_3O_4结中观察到了由反平行排列的Fe_3O_4电极的磁化引起的隧道磁电阻<0.4><2.6>效应，但其变化很小，仅为-0.5%。TMR的磁场依赖性表明，低的TMR可能与Fe_3O_4电极层表面磁化的超顺磁性行为有关。4.制备了非磁性MgO -磁性NiO双层绝缘层的Fe_3O_4/NiO/MgO/NiO/Fe_3O_4结结构。然而，由于大的结面积和薄至1 nm的NiO层引起的一些问题，没有获得预期的结特性。为了克服这些问题，需要采用光刻等先进工艺来制作精细结构。