Co_2Cr_<0.6>Fe_<0.4>Al薄膜を用いたエピタキシャル強磁性トンネル接合の製作とトンネル磁気抵抗特性

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Fully epitaxial magnetic tunnel junctions (MTJs) were fabricated with a full-Heusler alloy Co_2Cr_<0.6>Fe_<0.4>Al (CCFA) thin film and a MgO tunnel barrier. Cross-sectional high-resolution transmission electron microscope observations clearly showed that all layers of CCFA/MgO/Co_<50>Fe_<50> MTJ layer structures were grown epitaxially and were single-crystalline. The fully epitaxial CCFA/MgO/Co_<50>Fe_<50> MTJs, where we used the difference in the coercive forces to form the antiparallel magnetization configurations between the lower and upper electrodes, demonstrated high tunnel magnetoresistance (TMR) ratios of 90% at room temperature (RT) and 240% at 4.2 K. This result suggested that a CCFA film composition close to the stoichiometric one is essential for obtaining high spin polarizations in CCFA thin films. The fully epitaxial CCFA/MgO/Co_<50>Fe_<50> MTJs with exchange-biasing, where a Co_<50>Fe_<50> upper electrode was used in a synthetic ferrimagnetic Co_<50>Fe_<50>/Ru/Co_<90>Fe_<10> trilayer exchange-biased with an IrMn layer through the Co_<90>Fe_<10>/IrMn interface, exhibited high TMR ratios of 109% at RT and 317% at 4.2 K. From the obtained TMR ratio of 317% at 4.2 K, a high tunneling spin polarization of 0.88 at 4.2 K was estimated for epitaxial CCFA films with the B2 structure. These results confirm the promise of an epitaxial MTJ using a Co-based full-Heusler alloy as a key device structure for utilizing the potentially high spin polarization of this material system.
社団法人日本磁気学会の論文
2007-07-01

Co_2Cr_<0.6>Fe_<0.4>Al薄膜を用いたエピタキシャル強磁性トンネル接合の製作とトンネル磁気抵抗特性

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