Structural, optical and magnetic properties of Zn1−xMnxAl2O4 (0 ⩽ x ⩽ 0.5) spinel nanostructures by one-pot microwave combustion technique

Abstract

Zn1−xMnxAl2O4 (0⩽x⩽0.5) spinel nanostructures were synthesized by urea assisted microwave combustion method. Structural, vibrational, morphological, optical and magnetic properties were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), high resolution scanning electron microscopy (HR-SEM), UV–visible diffuse reflectance spectroscopy (DRS) and photoluminescence (PL) spectroscopy, and vibrating sample magnetometry (VSM) respectively. The XRD studies showed that the samples have pure cubic spinel phase, which is further validated by Rietveld refinement. The average crystallite size is of the nanoparticles estimated using Debey–Scherrer’s method was found to be in the range of 14–17nm. The lattice parameter is increased from 8.089 to 8.160Å with increasing in Mn2+ content. The William–Hall (W–H) analysis was used to study the effects of lattice strain over the crystallite size. Increase in lattice parameter and increase in porosity were observed on increasing Mn2+ concentration FTIR spectra showed the vibrational stretching frequencies corresponding to the zinc aluminate spinels. The morphology of the samples depicted the formation of well developed nano-sized clusters with homogeneous well crystallized grains without any agglomerations. The optical band gap value of undoped zinc aluminate nanostructure is higher than the reported bulk zinc aluminate. The direct band gap estimated using Kubelka–Munk method decreased with increasing Mn2+ content (5.05–3.49eV), due to the formation of sub bands in the energy gap. The photoluminescence characteristics of undoped and Mn2+ doped zinc aluminates are suggestive of defect controlled process and had an effect on the luminescence. Magnetic measurements revealed that the undoped ZnAl2O4 has diamagnetic behavior while the Mn2+ doped ZnAl2O4 system has superparamagnetic behavior.