Magnetic Properties of Zn0.8(Fe0.1,Co0.1)O Diluted Magnetic Semiconductors: Experimental and Theoretical Investigation
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- Mounkachi, O., Boujnah, M., Labrim, H. et al. J Supercond Nov Magn (2012) 25: 1515. doi:10.1007/s10948-012-1416-5
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Structural and magnetic properties of Zn0.8(Fe0.1, Co0.1)O bulk diluted magnetic semiconductor have been investigated using X-ray diffraction (XRD) and magnetic measurements. TEM (Transmission Electron Microscopy) images confirmed the high crystallinity and grain size of Zn0.8(Fe0.1,Co0.1)O powder, the samples were characterized by energy dispersive spectroscopy (EDS) to confirm the expected stoichiometry. This sample has been synthesized by co-precipitation route. The study of magnetization hysteresis loop measurements infers that the bulk sample of Zn0.8(Fe0.1,Co0.1)O shows a well-defined hysteresis loop at Tc (200 K) temperature, which reflects its ferromagnetic behavior. Hydrogenation treatment was used for the control of phase separation. Based on first-principles spin-density functional calculations, using the Korringa–Kohn–Rostoker method (KKR) combined with the coherent potential approximation (CPA), the ferromagnetic state energy was calculated and compared with the local-moment-disordered (LMD) state energy. The mechanism of hybridization and interaction between magnetic ions in Zn0.8(Fe0.1,Co0.1)O is also investigated.
KeywordsDiluted magnetic semiconductorsFerromagnetismHydrogen treatmentAb-initio calculationZnOSpintronic
During the last few years, there has been extensive interest in the diluted magnetic seminconductors (DMS) for their potential application in spintronic devices that allow the control of both the spin and charge carriers . Diluted magnetic semiconductor have been obtained by doping a non-magnetic semiconductor with transition metal ions. The first diluted magnetic semiconducting property was observed in intrinsically p-type Mn-doped GaAs around 110 K . Dietel et al. predicted that Mn doped p-type ZnO should be ferromagnetic above room temperature . Due to its wide bandgap (3.44 eV) and large excitation binding energy (60 MeV), transition metal doped ZnO is expected to play an important role in multidisciplinary areas of materials science and future spintronic devices .
Room temperature ferromagnetism in TM doped ZnO is proved by ab-initio calculation [5–9] and experimentally [10, 11]. However, the controversy between the intrinsic or extrinsic ferromagnetism must be clarified before one can really design the related devices. A number of researchers have successfully reported a Curie temperature Tc higher than room temperature in many TM-doped ZnO samples [10, 11]. On the contrary, many groups have failed to observe the room temperature ferromagnetism in these systems [12, 13]. Experimentally, the prediction of high temperature ferromagnetism depends on a large number of experimental parameters: preparation methods, measurement techniques, substrate choice, unexpectedly carriers introduced during the synthesis, for example, H or O, and acceptor or donor defects. From this point of view, the effects of native defects in ZnO, carrier doping on Zn0.80Co0.10Fe0.10O are investigated in this paper.
The present study focuses the magnetic behaviors of the ZnO co-doped by Fe and Co. In order to seek a situation where the material gets half-metallic behavior and has high magnetic moment, the Co and Fe concentrations are fixed at 10%. The synthesis of nominal 10% of Co and Fe co-doped ZnO sample has been done by co-precipitation method.
X-ray diffraction data related that Zn0.80Co0.10Fe0.10O crystallizes in the wurtzite structure with the presence of ZnFe2O4 spinel ferrite, following hydrogen treatment. DC magnetization measurement showed that the sample is ferromagnetic. However, a large increase in the magnetization is observed below 200 K. The origin of ferromagnetism is likely to be the intrinsic characteristics of the Zn0.80Co0.10Fe0.10O with the presence of donor defect (O vacancies) confirmed by energy stability for ferromagnetic state with and without donor defect.
2 Experimental Procedure
Co-precipitation is a process in which a solid is precipitated from a solution containing other ions. These ions are included into the solid by substitution in the crystal lattice. Adsorption on the surface of the growing particles is one of the principle mechanisms of co-precipitation.
(Co and Fe)-doped ZnO powders were successfully prepared by a simple chemical precipitation method using (CoCl2⋅6H2O), FeCl2, and (ZnCl2⋅6H2O) chloride as the sources of Co, Fe, and Zn, respectively. The precursors were added in de-ionized water and mixed homogeneously and refluxed under air atmosphere to yield a uniform mixture of precursor at 80∘. Precipitation was done using aqueous NaOH solution, the reactants were constantly stirred using a magnetic stirrer until a pH level of >7 was achieved. The dropping rate must be well controlled for the chemical homogeneity. The precipitates were washed several times to remove the water-soluble impurities and free reactants and dried at 100 ∘C for 10 h. The spongy contents were filtered, dried and then powdered. Heating treatments of the synthesized powders were conducted at 600 ∘C for 4 h, the synthesis methods used were previously applied for simple doping in ZnO like Mn doped ZnO  and double doping like Mn and Ni in ZnO .
3 Results and Discussion of Experimental Investigation
The physical characterization was performed by X-ray diffractometer (Model: D8 Discover Bruker AXS Detector 2D Hi-Star Turbo Source Rotating Anode X-Ray Cu), while the magnetic characterization was done by Magnetic Properties Measurement System (MPMS-7XL, Quantum Design, Inc). The morphology and particle size of the as-prepared samples were determined by transmission electron microscopy (TEM) observations with an accelerating voltage of 200 kV. The stoichiometric compositions of the obtained powders were determined by EDS.
3.1 Structures Properties
3.2 Magnetic Properties
4 Results and Discussion of Theoretical Investigation
4.1 Computational Details
4.2 Results and Discussion
In conclusion, single crystalline Zn0.8(Fe0.1,Co0.1)O have been synthesized through a co-precipitation method. X-ray diffraction revealed that the Zn0.8(Fe0.1,Co0.1)O with hydrogenation treatment possess wurtzite structure. The samples were characterized by TEM and EDS to confirm the expected stoichiometry, high crystallinity, and grain size. Zn0.8(Fe0.1,Co0.1)O are ferromagnetic with Curie temperature ≈180 K. By electronic structure and energy stability for ferromagnetic state with and without donor defect, we demonstrated that the origin of ferromagnetism is likely to be the intrinsic characteristics of the Zn0.80(Co0.10Fe0.10)O with the presence of donor defect (O vacancies).
MACHIKANEYAMA2002v08: H. Akai, Department of Physics, Graduate School of Science, Osaka University, Machikaneyama 1-1, Toyonaka 560-0043, Japan, firstname.lastname@example.org.