Elsevier

Journal of Alloys and Compounds

Volume 730, 5 January 2018, Pages 399-407
Journal of Alloys and Compounds

Magnetic and electric properties of Ni-doped ZnO nanoparticles exhibit diluted magnetic semiconductor in nature

https://doi.org/10.1016/j.jallcom.2017.09.334Get rights and content

Highlights

  • Ni-doped ZnO nanopowders for tuning the physical properties as DMS materials.

  • The FL emission peak at 359 and 397 nm belongs to the exciton recombination.

  • Frustrated semiconducting behaviour of highly nickel doped ZnO materials.

  • Magnetic and magnetoelectric properties of nickel doped ZnO nanoparticles.

Abstract

Zn1-xNixO (x = 0.0, 0.03, 0.06, 0.09, 0.12, 0.15) nanoparticles were prepared by chemical synthesis route using hydroxyoxalate type precursors and thermal decomposition process. All the samples crystallize in hexagonal wurtzite structure. Nickel doping into the ZnO structure was confirmed by Energy Dispersive X-ray (EDX) spectroscopy, High Resolution Transmission Electron Microscopy (HRTEM) and UV-VIS spectroscopy. The absorption spectra show the increase in band gap with increasing doping parameter. Fluorescence (FL) spectra exhibits the excitonic peak at 354 nm relating to near band edge emission for undoped and nickel doped ZnO nanoparticles. The signature of ferromagnetism of the Zn0.91Ni0.09O sample has been evidenced by SQUID. Dielectric properties and magnetoelectric (ME) coupling of the samples have also been discussed.

Introduction

The application potentialities of dilute magnetic semiconductors (DMS) in spintronics have catapulted the research interest in these materials to a very high level [1], [2], [3], [4]. The spintronics application requires the ability to couple the electron charge and spin degrees of freedom. Magnetic ordering at ambient temperature is the bare necessity for such application. The doping of some transition metal elements in wide band gap semiconductor like ZnO is expected to exhibit ferromagnetic ordering at room temperature, owing to carrier mediated exchange interaction. Though mostly Co and Mn doped ZnO has been studied, only limited studies have been reported on Ni doped ZnO.

ZnO crystallize in hexagonal wurtzite structure with tetrahedrally-coordinated O2− and Zn2+ ions, stacked alternately along the c-axis. The compound has a large exciton binding energy of 60 meV and is a promising phosphor material for UV light emission [5], [6]. The relatively smaller Ni2+ ion in its tetrahedral coordination is expected to have a larger solubility in ZnO. However there are reports to the contrary. We are thus motivated to study the Ni doped ZnO compounds for doping concentrations of 3, 6, 9, 12 and 15% and to find the possible M-E coupling potentiality.

The ZnO:Ni nanoparticles are prepared by chemical precipitation process, which consists in the simultaneous addition of reactants as acetate salts and tetramethylammonium hydroxide. Hydroxyoxalate type precursors are precipitated and transformed into doped ZnO nanoparticles. The calcined precipitates were studied by XRD, TEM, Fourier Transform Infra-Red (FTIR) spectroscopy, UV-VIS, FL, Dielectric, SQUID and ME coupling measurements.

Section snippets

Experimental

The nanocrystalline Zn1-xNixO (x = 0, 0.03, 0.06, 0.09, 0.12, 0.15) samples were prepared by simple chemical precipitation method. Here Zinc acetate dehydrate, Nickel acetate and tetramethylammonium hydroxide (25% in water) were used as precursors with double distilled water as solvent. Aqueous solutions of acetates (0.5 M) were prepared using double distilled water as reaction medium by constant stirring using magnetic stirrer. To prepare Zn1−xNixO, firstly 0.5 ml tetramethylammonium hydroxide

Characterization techniques

The crystallographic structure has been characterized by X-ray diffraction using X-ray diffractometer (RIGAKU, Japan) with CuKα radiation (λ = 1.5418 Å) and scanning angle 2θ between 10° and 80°. The structure and morphology also have been verified by HRTEM. The wurtzite structure is further analyzed by FTIR in open air. The optical absorbance spectra have been studied by Parkin Elmer Lambda-35 UV-VIS spectro-photometer in 300–800 nm. Using Perkin Elmer LS 55 Fluorescence Spectrometer the

EDX and XRD analyses

The chemical compositions of the compounds formed are checked by resorting to energy dispersive X-ray (EDX) spectroscopy analysis. The EDX spectra of two samples, Zn0.94Ni0.06O and Zn0.91Ni0.09O, are presented as Fig. 1(a) and (b) respectively. The spectra of both the samples reveal the presence of the elements Zn, Ni, O, C, and Cu. The appearance of the peaks corresponding to the elements C and Cu have their origin in the copper grid. The EDX thus confirm the absence of impurity in the

Conclusions

The pure and doped Zn1-xNixO nanoparticles have been successfully prepared by chemical growth technique. XRD analysis confirms the substitution of the relatively smaller Ni2+ ion with tetrahedral coordination in the Zn2+ sites of host lattice in the compound for x = 0.03. A secondary phase of NiO with octahedral coordination appears in the compounds with x ≥ 0.06. The crystallite size for the compounds obtained from XRD analyses match with the grain size revealed in the TEM analyses thus

Acknowledgement

Authors are grateful to the CRF, IIT Kharagpur for TEM and SQUID study. This exertion is partly supported by minor research project (GRANT NO. - PSW 129/13-14) from UGC of India.

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