We investigated the structure and magneto-transport properties of magnetic junctions using a Co 2 Fe(Ga 0.5 Ge 0.5) Heusler alloy as ferromagnetic electrodes and a Cu(In 0.8 Ga 0.2)Se 2 (CIGS) semiconductor as spacers. Owing to the semiconducting nature of the CIGS spacer, large magnetoresistance (MR) ratios of 40% at room temperature and 100% at 8 K were obtained for low resistance-area product (RA) values between 0.3 and 3 X lm 2. Transmission electron microscopy observations confirmed the fully epitaxial growth of the chalcopyrite CIGS layer, and the temperature dependence of RA indicated that the large MR was due to spin dependent tunneling.
Heusler alloy-based lateral spin valves with ohmic contacts are prepared for the Co2Fe(Ga0.5Ge0.5)/Cu system by means of the top-down microfabrication process. The magneto-transport and microstructure are characterized to investigate the influence of the microfabrication route on the spin dependent transport of lateral spin valves systematically. A large non-local spin signal (△RS) of 17.3 mΩ is observed at room temperature, which is attributed to the highly spin-polarized Co2Fe(Ga0.5Ge0.5) ferromagnet and the clean Co2Fe(Ga0.5Ge0.5)/Cu interfaces confirmed by transmission electron microscopy. Based on the general expression of one-dimensional spin diffusion model, we discuss the importance of interfacial spin polarization in Heusler alloy-based lateral spin valves.
Although single-crystalline spinel (MgAl2O4)-based magnetic tunnel junctions (MTJs) are known to show a good bias voltage dependence of a tunnel magnetoresistance (TMR) ratio over MgO-based MTJs, no polycrystalline MgAl2O4-based MTJs exhibiting large TMR ratios have been grown previously due to the lack of crystallinity of the MgAl2O4 barrier. In this work, we demonstrate the growth of polycrystalline-based MTJs with large TMR ratios exceeding 240% and an improved bias voltage dependence compared to that of MgO-based MTJs. An ultra-thin CoFe/MgO seed layer on the amorphous CoFeB layer induced the growth of a highly (001)-textured MgAl2O4 barrier, which worked as a template layer for the solid epitaxy of CoFe grains during the crystallization of the CoFeB layers. High resolution scanning transmission electron microscopy shows lattice-matched epitaxy between the (001)-textured MgAl2O4 barrier and CoFe grains. This study demonstrates the industrial viability of MgAl2O4-based polycrystalline MTJs with an improved bias voltage dependence.
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