Disorder-enhanced spin polarization of the Zn1-xCoxO1-v concentrated magnetic semiconductor

Amorphous concentrated magnetic semiconductor Zn0.32Co0.68O1-v (v refers to oxygen vacancies) thin film was investigated by magnetic and electrical transport measurements as well as Andreev reflection spectroscopy. At a low temperature range, the electrons in the Zn0.32Co0.68O1-v are strongly localized, and electrical transport obeys the Efros variable range hopping law. Spin polarization was measured by Andreev reflection spectroscopy. As high as 64 + 5% of spin polarization was attained through fitting of the modified Blonder-Tinkham-Klapwijk (BTK) theory. This enhanced spin polarization of Zn0.32Co0.68O1-v likely relates with the structure disorder and high concentration of magnetic cobalt ions, which lead to a spin imbalance impurity band in the tail of the conduction band. Considering room temperature ferromagnetism and high spin polarization, this material appears to be promising for spintronics device applications.