Abstract
Growth models and high magnetic field (HMF) are employed to affect diluted magnetic performance of Co-doped ZnO (ZnO:Co) films which oxidize Co-Zn evaporated films at 300 °C for 120 min in open air. Nanograined boundaries and dense structure obtained in the co-deposition films are helpful to present a better diluted magnetic performance. Two phases of Zn and ZnO coexist in the films at a low oxidation temperature. Both the bilayer Co/Zn film and the application of HMF during the oxidation process offer an easy way to increase oxygen vacancies, which are inconducive to improve the ferromagnetism. The co-deposition 0 T film has the best diluted magnetic performance compared with the bilayer 0 T film. To be specific, saturation magnetization MS of the co-deposition 0 T film (100.1 emu/cm3) increases by 190%, squareness S increases from 0.31 to 0.75 and coercivity HC increases from 34.6 Oe to 183.5 Oe. With the application of HMF, the MS of the co-deposition films decreases by 44% to approximately 55.8 emu/cm3 and the HC increases to 118.4 Oe.
Highlights
Diluted magnetic semiconductors (DMS) possess degrees of freedom in both electronic charge and spin[1] and present fascinating perspectives for the spin-based devices with preferable performance.[2]
The ZnO:Co films are obtained by furnace cooling with and without 12 T high magnetic field (HMF)
The application of HMF leads to decrease the particle size of the co-deposition films, and leads to the disappearance of the smaller particles in the bilayer films. These results can be explained that the co-deposition growth reduces the defects and HMF affects the growth process
Summary
Diluted magnetic semiconductors (DMS) possess degrees of freedom in both electronic charge and spin[1] and present fascinating perspectives for the spin-based devices with preferable performance.[2] Among various DMS materials, ZnO doping transition element (Co, Mn, etc.) is one of the most attractive candidates as ZnO is a semiconductor material with a direct wide bandgap of 3.37 eV (at RT) and a large exciton binding energy (60 meV).[3] ZnO exhibits excellent optoelectronic and piezoelectric properties,[4] making it promising and multifunctional materials in magneto-optoelectronic field.[5] Compared with other elements, Co is one of the most popular dopants because of its much larger atomic magnetic moment in ZnO.[6] the origin of ferromagnetic mechanism at room temperature has not been extensively studied.[7,8,9,10] The correlation between the ferromagnetism structural defects (such as oxygen vacancies, Zn interstitials, Zn vacancies), nanograined boundaries and Co states (such as secondary phase and Co cluster) are discussed in previous studies These defects and nanoscale structure critically depend on growth process and conditions. The effects of HMF and growth models on dilute magnetic properties of the oxidized ZnO: Co films were explored
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