Transition metal and rare earth-doped ZnO: a comparison of optical, magnetic, and structural behavior of bulk and thin films (original) (raw)
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Structural; morphological; optical and magnetic properties of Mn doped ferromagnetic ZnO thin film
Applied Surface Science, 2012
The structural, optical and magnetic properties of the Zn 1-x Mn x O (0 < x < 0.05) thin films synthesized by sol-gel technique have been analyzed in the light of modification of the electronic structure and disorder developed in the samples due to Mn doping. The films are of single phase in nature and no formation of any secondary phase has been detected from structural analysis. Absence of magnetic impurity phase in these films confirmed from morphological study also. Increasing tendency of lattice parameters and unit cell volume has been observed with increasing Mn doping concentration. The incorporation of Mn 2+ ions introduces disorder in the system. That also leads to slight degradation in crystalline quality of the films with increasing doping. The grain size reduces with increase in Mn doping proportion. The band gaps shows red shift with doping and the width of localized states shows an increasing tendency with doping concentration. It is due to the formation of impurity band and trapping of Mn atoms, which leads to the generation of the defect states within the forbidden band. Photoluminescence (PL) spectra shows gradual decrease of intensity of exitonic and defect related peaks with increasing Mn doping. Defect mediated intrinsic ferromagnetism has been observed even at room temperature for 5at% Mn doped ZnO film. The strong presence of antiferromagnetic (AFM) interaction reduces the observed ferromagnetic moments.
With a view to understand the influence of nano size on various properties of cobalt-doped ZnO-based diluted magnetic semiconductors, a series of materials were prepared by the citrate gel route. The phase and morphology studies have been carried out by X-ray diffraction and transmission electron microscopy, respectively. All the samples of the present investigation are found to have hexagonal wurtzite structure and crystallite sizes are found to vary from 25 nm to 65 nm. From the optical absorption measurements it has been observed that upon doping with cobalt, the energy band gap is found to shift towards lower energy side (red shift) while it shifts towards higher energy side (blue shift) when the crystallite size is increased continuously. It has been observed from the XPS results that oxidation state of Cobalt is +2 and that the difference in binding energies of Co 2p 3/2 and Co 2p 1/2 is found to increase continuously with increasing crystallite size. Finally, all the samples are found to exhibit room temperature ferromagnetism and the specific magnetization decreases with increasing crystallite size.
ACS Applied Materials & Interfaces, 2013
In this article, we have investigated the effect of oxygen partial pressure (P O 2) and film thickness on defectinduced room-temperature (RT) ferromagnetism (FM) of highly c-axis orientated p-type Na-doped ZnO thin films fabricated by pulse laser deposition (PLD) technique. We have found that the substitution of Na at Zn site (Na Zn) can be effective to stabilize intrinsic ferromagnetic (FM) ordering in ZnO thin films with Curie temperature (T C) as high as 509 K. The saturation magnetization (M S) is found to decrease gradually with the increase in thickness of the films, whereas an increase in "M S " is observed with the increase in P O 2 of the PLD chamber. The enhancement of ferromagnetic signature with increasing P O 2 excludes the possibility of oxygen vacancy (V O) defects for the magnetic origin in Na-doped ZnO films. On the other hand, remarkable enhancement in the green emission (I G) are observed in the photoluminescence (PL) spectroscopic measurements due to Na-doping and that indicates the stabilization of considerable amount of Zn vacancy (V Zn)-type defects in Na-doped ZnO films. Correlating the results of PL and X-ray photoelectron spectroscopy (XPS) studies with magnetic measurements we have found that V Zn and Na substitutional (Na Zn) defects are responsible for the hole-mediated FM in Na-doped ZnO films, which might be an effective candidate for modern spintronic technology.
Extrinsic origin of ferromagnetism in doped ZnO
Journal of Materials Chemistry, 2006
Different synthetic routes have been tested to prepare bulk doped ZnO. The doping elements were Mn, Fe and Co. We were able to prepare single-phase compounds at high temperature by using ceramic procedures and at very low temperature using a sol-gel method. No ferromagnetism has been observed for these samples. In contrast, spontaneous magnetization is observed in samples obtained from non-optimal conditions and exhibiting secondary phases. Magnetic impurities have been easily identified for Fe-and Co-doped samples. However, the nature of the room temperature magnetic impurity for the Mn-based compound is not so clear and different possibilities are discussed. We have also checked the effect of the grain size on the magnetic properties by synthesizing nano-materials using a sol-gel route. The single-phase nano-compounds are also not ferromagnets showing similar properties to the well-sintered polycrystalline materials.
Structural and Magnetic Properties of Mn/Fe co-Doped ZnO Thin Films Prepared by Sol–Gel Technique
IEEE Transactions on Magnetics, 2014
Mn/Fe co-doped ZnO thin films are prepared by simple sol-gel and spin coating method. Five different sols with the change in concentration (1-5 wt%) of both Mn and Fe are synthesized. Molar ratio of Mn and Fe is kept constant, i.e., 1:1. Sols are spun onto glass and copper substrates by spin coating method followed by the post magnetic field annealing at 300°C for 1 h. Effect of Mn and Fe codoping on ferromagnetic properties of ZnO is reported in this paper. Structural and magnetic properties of as prepared and annealed samples are investigated by X-ray diffractometer (XRD) and vibrating sample magnetometer (VSM). Scanning electron microscope is used to study the surface morphology of co-doped films. XRD results show incorporation of Mn and Fe in the host lattice upto a dopant concentration of 4 wt%. However, small crystallites of Mn and Fe 2 O 3 are observed by increasing the dopant concentration to 5 wt%. VSM results indicate room temperature ferromagnetism in all samples without the presence of any secondary phases. Low value of shape anisotropy is observed in the case of Mn doped ZnO. However, no shape anisotropy is observed in the case of co-doped thin films. Moreover, Mn/Fe co-doped thin films show magnetic hysteresis equivalent to that of multilayered structure, indicating that such complex structures used in spintronic devices can be replaced by a single ZnO layer with codoping of Mn and Fe.
Applied Physics Letters, 2009
Spin electronics or spintronics, is an advanced technology which exploits the quantum spin states of electrons as well as making use of their charge state. Electron spin has two possible states, either "up" or "down." Aligning spins in a material creates magnetism. Moreover, magnetic fields affect the passage of "up" and "down" electrons differently. Controlling the spin of electrons within a device can produce surprising and substantial changes in its properties. Scientists have proposed the miniature of numerous spintronic devices, such as the magnetoresistive random access memory (MRAM), spin field effect transistor (Spin-FET), spin light emitting diode (Spin-LED), and quantum computer. The integration of magnetism, optics and electronics for the development of advanced spintronic devices is an extremely important research topic.