The TMR ratio of Co2Fe6B2/MgO-based p-MTJ spin valves stacked with a [Co/Pd]n-SyAF layer decreased rapidly when the ex situ magnetic annealing temperature (Tex) was increased from 275 to 325 °C, and this decrease was associated with degradation of the Co2Fe6B2 pinned layer rather than the Co2Fe6B2 free layer. At a Tex above 325 °C the amorphous Co2Fe6B2 pinned layer was transformed into a face-centered-cubic (fcc) crystalline layer textured from [Co/Pd]n-SyAF, abruptly reducing the Δ1 coherence tunneling of perpendicular-spin-torque electrons between the (100) MgO tunneling barrier and the fcc Co2Fe6B2 pinned layer.

For the perpendicular-magnetic-tunneling-junction (p-MTJ) spin valve with a nanoscale-thick bottom Co2Fe6B2 free layer ex situ annealed at 400 °C, which has been used as a common p-MTJ structure, the Pt atoms of the Pt buffer layer diffused into the MgO tunneling barrier. This transformed the MgO tunneling barrier from a body-centered cubic (b.c.c) crystallized layer into a mixture of b.c.c, face-centered cubic, and amorphous layers and rapidly decreased the tunneling-magnetoresistance (TMR) ratio. The p-MTJ spin valve with a nanoscale-thick top Co2Fe6B2 free layer could prevent the Pt atoms diffusing into the MgO tunneling barrier during ex situ annealing at 400 °C because of non-necessity of a Pt buffer layer, demonstrating the TMR ratio of ~143 %.Electronic supplementary materialThe online version of this article (doi:10.1186/s11671-016-1637-9) contains supplementary material, which is available to authorized users.

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The dielectric functions of undoped and P-doped Si1−xGex (SiGe) films with a compressive strain on silicon-on-insulator (SOI) substrates are obtained by using spectroscopic ellipsometry. The respective Kato–Adachi and Tauc–Lorentz models are best fitted to the undoped and P-doped SiGe films to obtain their complex dielectric functions. The undoped SiGe films are characterized by multimodal peaks in the dielectric function, whereas the P-doped SiGe films exhibit only a broad peak. Further, the E0 and E1 critical points (CPs) of the undoped SiGe films are strongly dependent on the Ge concentration, whereas the E2 CPs are independent of concentration. The E0 and E2 CPs in the undoped SiGe films on an SOI substrate are lower than those of SiGe on a bulk-Si substrate owing to the higher strain. For P doping in SiGe, its dose causes non-monotonic variations in Eg and E0.