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Analysis and control of spin polarization of half-metallic ferromagnets by the use of runneling junctions

利用隧道结分析和控制半金属铁磁体的自旋极化

基本信息

批准号：
12450009
负责人：
ASANO Hidefumi
金额：
$ 8万
依托单位：
Nagoya University
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (B)
财政年份：
2000
资助国家：
日本
起止时间：
2000 至 2001
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/en/grant/KAKENHI-PROJECT-12450009/
关键词：
tunneling effect half-metal spin polarization tunnel junction La_<0.7>Sr_<0.3>MnO_3 Sr_2FeMoO_6 magneto-resistance Fe_3O_4

项目摘要

Tunnel junctions of Co_<0.9>Fe_<0.1>/SrTiO_3/La_<0.7>Sr_<0.3>MnO_3 (LSMO) were investigated in order to elucidate the factors affecting the spin polarization of interfaces of ferromagnets. Through the evaluation of junction magnetoresistance (MR) at 4.2 K and the high resolution Rutherford backscattering technique, it is found that the origin of inter facial degradation is the oxygen deficiencies in the SrTiO_3 barriers. The local densities of states at the Co_<0.9>Fe_<0.1> interface deduced from the bias voltage (V) dependence of MR conincide well with the results of the first principle calcualtion, indicating that the Co_<0.9>Fe_<0.1> interface is of high quality. In the LSMO juncttions, the MR effects disappear at temperatures of around 200 K well below the ferromagnetic transition temperature T_c of 360 K, which indicates that the spin polarization of LSMO interface goes down to zero at the temperatures.As an alternative of LSMO, high T_c half-metallic ferromagnets Sr_2FeMoO_6 and Fe_3O_4 were investigated with respect to their fundamental properties. For thin films of Sr_2FeMoO_6, which were grown by sputtering in an Ar+H_2 gas atmosphere, the effects of lattice-mismatch induced strain and its relaxation process on the magnetization and transport properties have been elucidated, and high quality films with a full magnetization have been realized by measns of a lattice-matched buffer layer technique. This strongly indicates the half metalicity of Sr_2FeMoO_6 films at the ground state. Considering the high T_c (42O K) of Sr_2FeMoO_6, a high spin polarlization of 0.7 at RT is expected. Moreover, as for Fe_3O_4, high quality urtra thin films showing Verway transition have been obtained. For realization of high T_cjunctions, insulating barrier materials such as A1N is shown to be promising.

研究了Co_ Fe<0.9>_3<0.1>/SrTiO_3/La_<0.7>Sr_<0.3>MnO_3（LSMO）隧道结，以阐明影响铁磁体界面自旋极化的因素。通过对4.2K下的结磁电阻（MR）和高分辨卢瑟福背散射（Rutherford Backscattering）技术的研究，发现SrTiO_3势垒中的氧缺陷是界面退化的根源。由<0.9><0.1>磁电阻的偏压（V）关系导出的Co_ Fe_2界面的局域态密度与第一性原理计算结果符合得很好，表明Co_<0.9>Fe_2<0.1>界面是高质量的。在LSMO结中，当温度低于铁磁转变温度T_c（360 K）时，MR效应消失，表明LSMO界面的自旋极化在此温度下趋于零。对于在Ar+H_2气氛中溅射生长的Sr_2FeMoO_6薄膜，本文阐明了晶格失配引起的应变及其弛豫过程对磁化强度和输运性质的影响，并通过晶格匹配缓冲层技术获得了具有完全磁化强度的高质量薄膜。这表明Sr_2FeMoO_6薄膜在基态具有半金属性。考虑到Sr_2FeMoO_6的高T_c（420 K），室温下的自旋极化率可望达到0.7。对于Fe_3O_4，也得到了具有Verway转变的高质量超薄膜。为了实现高T_c结，绝缘阻挡层材料如AlN被证明是有希望的。