Magnetoresistance ratio of more than 1% at room temperature in germanium vertical spin-valve devices with Co2FeSi

We report the highest two-terminal magnetoresistance (MR) ratio at room temperature in semiconductor (SC)-based vertical spin-valve (VSV) devices on a silicon (Si) platform. Here, we demonstrate all-epitaxial ferromagnet (FM)–germanium (Ge)–FM VSV devices with Co2FeSi as one of two FM electrodes. In addition to the high spin polarization of Co2FeSi, the relatively low resistance in the parallel magnetization state due to the strong Fermi-level-pinning effect at the p-type Ge/Co2FeSi interface causes the enhancement in the MR ratios. As a result, we achieve two-terminal MR ratios of over 1% even at room temperature through a 20-nm-thick Ge intermediate layer in VSV devices on Si. We emphasize that the use of Co-based Heusler alloys is effective even for SC-based VSV structures on Si to obtain high MR ratios at room temperature.