A half-metal is an ideal spin source to realize extremely large magnetoresistance effects because of the completely spin-polarized density of states at the Fermi level, and Heusler alloy is a material class for which several compositions are known to exhibit half-metallic properties. Current perpendicular-to-plane (CPP) giant magnetoresistance (GMR) effect is a resistance change that depends upon the relative angle of the magnetization vectors in magnetic layers separated by thin non-magnetic layer(s), which can be utilized for magnetic sensor applications. Over the last decade, the resistance change of CPP-GMR has been found to enhance greatly when using half-metallic Heusler alloys. In this article, the history of Heusler alloy based CPP-GMR is briefly reviewed, including the authors’ recent results on the analysis of the spin asymmetry coefficients based on the Valet-Fert model. Finally, the degradation of half-metallic spin polarization at interfaces is discussed and a future prospect is described.
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