The correlation of spin injection efficiency and interfacial resistance is investigated in La0.67Sr0.33MnO3 (LSMO)/Alq3/Co organic spin-valve devices. When a thin layer of copper phthalocyanine (CuPc) is inserted between LSMO and Alq3, the magnetoresistance (MR) of the device decrease to only ∼0.4% at 50 K, in sharp contrast to ∼6% MR ratio at the same bias voltage for the device without CuPc interlayer. Meanwhile, the electrical resistance decreases by one order of magnitude, indicating that the interface barrier height is reduced. These results reflect that a strong correlation between the significant decrease of spin injection efficiency at LSMO/CuPc interface and the reduced interfacial resistance. The findings indicate that the conductivity mismatch problem is applicable to organic materials and the interfacial resistance has important impact on the spin injection efficiency.

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