Emergent carrier spin polarization in (Fe, Al)-codoped ZnO thin films explored by Andreev Reflection spectroscopy

The carrier spin polarization of magnetic materials is one of the most critical elements for current-driven spintronics devices. Experimental evidence of spin polarization of magnetic oxides is still a matter of considerable debate although room-temperature ferromagnetism was reported in nearly all doped/undoped oxides materials. In this work, we systematically study the carrier spin polarization and non-uniform magnetization scattering of Zn1_xFexAl0.01O (x = 0.05, 0.10) thin films in metallic regime. Spin polarization 65 +/- 8% is confirmed experimentally for Zn0.95Fe0.05Al0.01O by Andreev Reflection spectroscopy, which reduces to 40 +/- 5% for Zn0.90Fe0.10Al0.01O as Fe doping level increases to 10%. Magnetoresistance and Anomalous Hall effect are observed in Zn1_ xFexAl0.01O films which corroborates the spin-polarized carrier in spin-split bands close to the Fermi level. Furthermore, combining element mapping and Andreev reflection spectra, our results support that non-uniform magnetization of Zn1_ xFexAl0.01O films which introduces large inelastic spin-flip scattering at the interface of Zn1_xFexAl0.01O/Pb superconducting junctions, and consequently reduction of spin polarization. The spin-polarized carrier and transport behaviors in Zn1_xFexAl0.01O magnetic oxides provide the reliable evidence to identify the intrinsic ferromagnetism and an excellent platform for spintronics device applications.