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

Abstract

Amorphous concentrated magnetic semiconductor Zn_0.32Co_0.68O_1−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 Zn_0.32Co_0.68O_1−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 Zn_0.32Co_0.68O_1−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.