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.

为了利用半金属性质的过渡金属氧化物在隧道结中实现大磁阻效应，研究了结的最佳制造条件以及铁磁氧化物的表面磁性对隧道磁阻的影响。结果总结如下： 1.薄化。采用脉冲激光沉积(PLD)技术在低温下生长了高质量的Fe_3O_4和MgO薄膜。即使在1 x 10^<-5> Torr的氧压下，也可以在低于200℃的温度下生长，以防止结的制造过程中Fe_3O_4表面的氧化，具有半金属性质的Sr_2FeMoO_6薄膜是一种很有前途的薄膜。候选的铁磁电极在500℃下成功生长，低于报道的生长温度。2.MgO的最佳PLD生长条件对最佳条件下制备的Fe_3O_4/MgO/Au结结构的电流-电压特性进行了测定，结果表明，MgO绝缘层厚度为1 nm的结具有良好的隧道质量。3、隧道磁阻效应(TMR)。观察到反平行排列的 Fe_3O_4 电极的磁化强度Co_<0.4>Fe_<2.6>O_4/Fe_3O_4/MgO/Fe_3O_4结，尽管TMR变化低至-0.5%。TMR的磁场依赖性表明，低TMR可能与表面的超顺磁行为有关。 4.Fe_3O_4电极层的磁化强度制备了具有非磁性MgO-磁性NiO双绝缘层的Fe_3O_4/NiO/MgO/NiO/Fe_3O_4结结构，但由于结面积大和NiO层薄而导致的一些问题，没有获得预期的结性能。 1 nm 需要先进的制造精细结构的工艺，如光刻技术来克服这些问题。