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

TL;DR

This study investigates how oxygen vacancies and nano grain size influence the spin polarized current in Co-doped ZnO thin films, revealing methods to enhance spin polarization for spintronic applications.

Contribution

It demonstrates that increasing oxygen vacancies and reducing grain size significantly enhance the spin polarized current in diluted magnetic oxides, providing practical strategies for spintronic device optimization.

Findings

Oxygen vacancies increase conductivity via VRH and itinerant transport.

VRH conduction correlates with spin polarized current.

Reducing grain size and lattice constants boosts VRH and spin polarization.

Abstract

Spin polarized current is the main ingredient of diluted magnetic oxides due to its potential manipulation in spintronic devices. However, most research has focused on ferromagnetic properties rather than polarization of electric current, because direct measurements were difficult and the origin of spin polarized currents has yet to be fully understood. The method to increase the spin polarized current percentage is beyond practical consideration at the present status. To target this problem, we focus on the role of oxygen vacancies and nano grain size on the spin polarized current, which are controlled by growing the Co-doped ZnO thin-films at room temperature in a reducing atmosphere [Ar + (1% ~ 30%) H2]. We found that the conductivity increases with an increase in oxygen vacancies via two independent channels: the variable range hopping (VRH) within localized states and the itinerant transport in the conduction band. The Andreev Reflection measurements prove that the VRH conduction is equivalent to spin polarized current. Transport measurements show that the best way to increase the VRH content, or the percentage of spin polarized current, is to increase oxygen vacancy concentration and to reduce grain size and lattice constants of the films.