Eur. Phys. J. Appl. Phys. (2014) 67: 10401
https://doi.org/10.1051/epjap/2014140074

Structural, EPR and optical properties of Zn_0.75TM_0.25O (TM = Mn, Fe, Co, Ni) aerogel nanoparticles

¹ Department of Physics, Faculty of Science, King Abdulaziz University, North Jeddah Branch, PO Box 80203, Jeddah 21589, Saudi Arabia
² Équipe de Spectroscopie Raman, Département de Physique, Faculté des Sciences de Tunis, Campus Universitaire, El-Manar, 2092 Tunis, Tunisia
³ Al Imam Mohammad Ibn Saud Islamic University (IMSIU), College of Sciences, Department of Physics, Riyadh 11623, Saudi Arabia
⁴ Laboratory of Physics of Materials and Nanomaterials Applied at Environment (LaPhyMNE), Gabes University, Faculty of Sciences in Gabes, 6072 Gabes, Tunisia
⁵ Institut des NanoSciences de Paris (INSP) UMR CNRS 7588, Universités Pierre et Marie Curie (Paris 6) et Denis Diderot (Paris 7), Campus Boucicaut, 140 rue de Lourmel, 75015 Paris, France

^a email: amor.sayari@laposte.net

Received: 23 February 2014
Revised: 7 April 2014
Accepted: 12 May 2014
Published online: 17 June 2014

Abstract

ZnO nanopowders with different 3d transition metal (TM) doping (TM = Mn, Fe, Co, Ni) were synthesized by a new protocol based on slow hydrolyse of zinc acetate dissolved in methanol and supercritical drying in ethyl alcohol. The prepared Zn_1−xTM_xO (x = 0.25) nanoparticles were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), differential scanning calorimetry (DSC), optical absorption and electron paramagnetic resonance spectroscopy (EPR). The results demonstrated that the TM dopant significantly affects the structural and magnetic properties of the samples. From the XRD spectra, the lattice parameters, average crystallite size and microstrain values were obtained. All ZnTMO nanoparticles show an expansion of the lattice parameters compared those of the bulk samples. Unit cell volume was minimized with Fe doping and increased as the atomic number of the dopant moved away from Fe. The XRD pattern indicates the formation of hexagonal wurtzite phase of ZnO for all the TM dopants. Electron microscopy characterization showed that the size of the Zn_1−xTM_xO particles is about 25 nm did not change significantly for the different dopants. Optical absorption measurements show that band gap energies of the TM-doped ZnO nanoparticles are around 3.2 eV. The Urbach energy of the ZnTMO nanopowders varies with the TM dopant. From magnetic measurements we observed the presence of room temperature ferromagnetic order in our TM-doped ZnO samples. EPR spectra confirm that TM ions were mainly incorporated as TM²⁺, occupying the Zn²⁺ sites in the wurtzite structure of ZnO. Room temperature ferromagnetic order was observed only in Ni- and Co-doped ZnO samples, whereas Mn- and Fe-doped powders showed only antiferromagnetic and paramagnetic interactions, respectively. The correlation between the structural and magnetic properties as a function of the TM dopant is discussed.