We present direct link between the transport properties of Co2 MnSi and Co2 FeMnSi Heusler based current-perpendicular-to-plane spin valves (CPP-SVs) and interface atomic structures resolved by aberration-corrected electron microscopy. The structure of the Co2 FeMnSi electrodes is L21 but their interface with the CoSi spacer is disordered. In contrast to the Co2 FeMnSi -electrodes, the Co 2 MnSi -electrodes have abrupt interfaces with the Ag spacer though their ordering is not fully L21. The magnetoresistance of the Co 2 MnSi-SV is over two orders of magnitude better than those of Co2 FeMnSi-SV, demonstrating that the atomic interface ordering is crucial for the enhancement of the magnetoresistance in the Heusler CPP-SVs.
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