Direct observation of hopping induced spin polarization current in oxygen deficient Co-doped ZnO by Andreev reflection technique

2017 ◽

Vol 31 (31) ◽

pp. 1750247

Author(s):

Qingyu Huo ◽

Zhenchao Xu ◽

Linfeng Qu

Keyword(s):

Absorption Spectrum ◽

Spin Polarization ◽

Electron Spin ◽

Magnetic Moments ◽

The State ◽

Band Gaps ◽

Electron Spin Polarization ◽

Approximation Formula ◽

Doped Zno ◽

Co Doped

Both blue and red shifts in the absorption spectrum of Co-doped ZnO have been reported at a similar concentration range of doped Co. Moreover, the sources of magnetism of Co-doped ZnO are controversial. To solve these problems, the geometry optimization and energy of different Co-doped ZnO systems were calculated at the states of electron spin polarization and nonspin polarization by adopting plane-wave ultra-soft pseudopotential technology based on density function theory. At the state of electron nonspin polarization, the total energies increased as the concentration of Co-doped increased. The doped systems also became unstable. The formation energies increased and doping became difficult. Furthermore, the band gaps widened and the absorption spectrum exhibited a blue shift. The band gaps were corrected by local-density approximation + [Formula: see text] at the state of electron spin polarization. The magnetic moments of the doped systems weakened as the concentration of doped Co increased. The magnetic moments were derived from the coupling effects of [Formula: see text]–[Formula: see text]. The band gaps narrowed and the absorption spectrum exhibited a red shift. The inconsistencies of the band gaps and absorption spectrum at the states of electron spin polarization and nonspin polarization were first discovered in this research, and the sources of Co-doped ZnO magnetism were also reinterpreted.

Download Full-text

Spin Manipulation in Co-Doped ZnO

Advances in Science and Technology ◽

10.4028/www.scientific.net/ast.67.192 ◽

2010 ◽

Vol 67 ◽

pp. 192-197 ◽

Cited By ~ 2

Author(s):

Heidemarie Schmidt

Keyword(s):

Spin Polarization ◽

Electron Concentration ◽

Schottky Diodes ◽

Weak Localization ◽

Spin Splitting ◽

Zno Films ◽

Polarized Electrons ◽

Spin Polarized ◽

Doped Zno ◽

Co Doped

The magnetoresistance of n-type conducting, paramagnetic Co-doped ZnO films prepared by pulsed laser deposition on sapphire substrates has been studied experimentally and theoretically. Positive magnetoresistance (MR) of 124% has been observed in the film with the lowest electron concentration of 8.3·1017 cm−3, while only a negative MR of −1.9% was observed in the film with an electron concentration of 9.9·1019 cm−3 at 5 K. The positive MR is attributed to the quantum correction on the conductivity due to the <em>s</em>-<em>d </em>exchange interaction induced spin splitting of the conduction band. The negative MR is attributed to the magnetic field suppressed weak localization [1]. Voltage control of the electron concentration in Schottky diodes revealed a drastic change of the magnetoresistance and demonstrated the electrically controllable magnetotransport behavior in Co-doped ZnO [2]. The magnetically controllable spin polarization in Co-doped ZnO has been demonstrated at 5 K in magnetic tunnel junctions with Co-doped ZnO as a bottom electrode and Co as a top electrode [3]. There spin-polarized electrons were injected from Co-doped ZnO to a crystallized Al2O3 layer and tunnelled through an amorphous Al2O3 barrier. Our studies demonstrate the spin polarization and manipulation in Co-doped ZnO.

Download Full-text

Influence of N Dopant on the Electric and Magnetic Properties of Co Doped ZnO Thin Films

Journal of Inorganic Materials ◽

10.3724/sp.j.1077.2010.00711 ◽

2010 ◽

Vol 25 (7) ◽

pp. 711-716 ◽

Cited By ~ 3

Author(s):

Xue-Tao WANG ◽

Li-Ping ZHU ◽

Zhi-Gao YE ◽

Zhi-Zhen YE ◽

Bing-Hui ZHAO

Keyword(s):

Thin Films ◽

Magnetic Properties ◽

Zno Thin Films ◽

Doped Zno ◽

Co Doped

Download Full-text

Photoluminescence and Magnetic Properties of Undoped and (Mn, Co) co-doped ZnO Nanoparticles

Current Nanoscience ◽

10.2174/1573413715666191010162626 ◽

2020 ◽

Vol 16 (4) ◽

pp. 655-666

Author(s):

Mona Rekaby

Keyword(s):

Magnetic Properties ◽

Zno Nanoparticles ◽

Room Temperature ◽

Magnetic Measurements ◽

Structural Defects ◽

Ferromagnetic Behavior ◽

Secondary Phases ◽

Antiferromagnetic Ordering ◽

Doped Zno ◽

Co Doped

Objective: The influence of Manganese (Mn2+) and Cobalt (Co2+) ions doping on the optical and magnetic properties of ZnO nanoparticles was studied. Methods: Nanoparticle samples of type ZnO, Zn0.97Mn0.03O, Zn0.96Mn0.03Co0.01O, Zn0.95Mn0.03 Co0.02O, Zn0.93Mn0.03Co0.04O, and Zn0.91Mn0.03Co0.06O were synthesized using the wet chemical coprecipitation method. Results: X-ray powder diffraction (XRD) patterns revealed that the prepared samples exhibited a single phase of hexagonal wurtzite structure without any existence of secondary phases. Transmission electron microscope (TEM) images clarified that Co doping at high concentrations has the ability to alter the morphologies of the samples from spherical shaped nanoparticles (NPS) to nanorods (NRs) shaped particles. The different vibrational modes of the prepared samples were analyzed through Fourier transform infrared (FTIR) measurements. The optical characteristics and structural defects of the samples were studied through Photoluminescence (PL) spectroscopy. PL results clarified that Mn2+ and Co2+ doping quenched the recombination of electron-hole pairs and enhanced the number of point defects relative to the undoped ZnO sample. Magnetic measurements were carried out at room temperature using a vibrating sample magnetometer (VSM). (Mn, Co) co-doped ZnO samples exhibited a ferromagnetic behavior coupled with paramagnetic and weak diamagnetic contributions. Conclusion: Mn2+ and Co2+ doping enhanced the room temperature Ferromagnetic (RTFM) behavior of ZnO. In addition, the signature for antiferromagnetic ordering between the Co ions was revealed. Moreover, a strong correlation between the magnetic and optical behavior of the (Mn, Co) co-doped ZnO was analyzed.

Download Full-text

Sol-gel preparation and properties of electroconductive Sn–Al co-doped ZnO coated TiO2 whisker and its applications in textiles

Materials Science in Semiconductor Processing ◽

10.1016/j.mssp.2020.105607 ◽

2021 ◽

Vol 124 ◽

pp. 105607

Author(s):

Ziao Xu ◽

Yanan Zhu ◽

Zengyuan Pang ◽

Mingqiao Ge

Keyword(s):

Sol Gel ◽

Doped Zno ◽

Gel Preparation ◽

Co Doped

Download Full-text

Optimizing physical properties of Co-doped ZnO nanoparticles: Controlling oxygen vacancy and carrier concentration

Vacuum ◽

10.1016/j.vacuum.2021.110488 ◽

2021 ◽

pp. 110488

Author(s):

Huying Yan ◽

Jian Xue ◽

Wenjing Chen ◽

Jialing Tang ◽

Ling zhong ◽

...

Keyword(s):

Oxygen Vacancy ◽

Physical Properties ◽

Carrier Concentration ◽

Zno Nanoparticles ◽

Doped Zno ◽

Co Doped

Download Full-text

Transport mechanisms in Co-doped ZnO (ZCO) and H-irradiated ZCO polycrystalline thin films

Physical Chemistry Chemical Physics ◽

10.1039/d0cp06401g ◽

2021 ◽

Vol 23 (3) ◽

pp. 2368-2376

Author(s):

A. Di Trolio ◽

A. Amore Bonapasta ◽

C. Barone ◽

A. Leo ◽

G. Carapella ◽

...

Keyword(s):

Thin Films ◽

Opposite Effect ◽

Transport Mechanisms ◽

Co Doping ◽

Polycrystalline Thin Films ◽

Doped Zno ◽

Co Doped

Co doping increases the ZnO resistivity (ρ) at high T (HT), whereas it has an opposite effect at low T (LT). H balances the Co effects by neutralizing the ρ increase at HT and strengthening its decrease at LT.

Download Full-text