Origin and Enhancement of Spin Polarization Current in Diluted Magnetic Oxides by Oxygen Vacancies and Nano Grain Size

摘要

Spin polarized current is the main ingredient of diluted magnetic oxides dueto its potential manipulation in spintronic devices. However, most research hasfocused on ferromagnetic properties rather than polarization of electriccurrent, because direct measurements were difficult and the origin of spinpolarized currents has yet to be fully understood. The method to increase thespin polarized current percentage is beyond practical consideration at thepresent status. To target this problem, we focus on the role of oxygenvacancies and nano grain size on the spin polarized current, which arecontrolled by growing the Co-doped ZnO thin-films at room temperature in areducing atmosphere [Ar + (1% ~ 30%) H2]. We found that the conductivityincreases with an increase in oxygen vacancies via two independent channels:the variable range hopping (VRH) within localized states and the itineranttransport in the conduction band. The Andreev Reflection measurements provethat the VRH conduction is equivalent to spin polarized current. Transportmeasurements show that the best way to increase the VRH content, or thepercentage of spin polarized current, is to increase oxygen vacancyconcentration and to reduce grain size and lattice constants of the films.