Current spin polarization and spin injection efficiency in ZnO-based ferromagnetic semiconductor junctions

[FeNi(3 nm)/Zn1−xCoxO(3 nm)]2/ZnO(d nm)/[Zn1−xCoxO(3 nm)/Co(3 nm)]2 (d=3 and 10) semiconductor junctions were prepared by magnetron sputtering system and photolithography. The spin valve effiect was observed in these junctions because the utility of the ferromagnetic composite layers acted as soft and hard magnetic layers. The electrical detection was performed by measuring the magnetoresistance of these junctions to investigate the current spin polarization αsc in the ZnO layer and the spin injection efficiency η of spin-polarized electrons. αsc was reduced from 11.7% (and 10.5%) at 90 K to 7.31% (and 5.93%) at room temperature for d=3 (and d=10). And η was reduced from 39.5% (and 35.5%) at 90 K to 24.7% (and 20.0%) at room temperature for d=3 (and d=10).