Recent report of large MR ratio over 70% at RT using a Co₂Fe_0.4Mn_0.6Si-based current-perpendicular-to-plane giant magnetoresistance (CPP-GMR) devices by Sato et al. indicates great potential of half-metallic Heusler-based CPP-GMR devices. However, there is no systematic studies on the effect of the replacement of Mn by Fe on the MR enhancement. In this seminar, we will report our recent systematic studies on the MR properties of CPP-GMR using Co₂Fe_1-xMn_xSi (CFMS) Heuser alloys. Spin-torque induced oscillation based on the CFMS-based CPP-GMR will be also presented.