Modified structural and magnetic properties of nanocrystalline MnFe2O4 by pH in capping agent free co-precipitation method

Nano-sized manganese ferrite (MnFe2O4) particles were prepared using co-precipitation method in two different pH (9 and 11). The structural, morphological, optical and magnetic properties of as-synthesized nanoparticles were characterized by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), transmission electron microscopy (TEM), UV-vis absorption and vibrating sample magnetometer (VSM). The FTIR spectra revealed two strong peaks at about 600 and 400 cm(-1) that can be attributed to the vibration mode of octahedral and tetrahedral sites of spinel structure of MnFe2O4, respectively. The XRD results showed that the nanocrystalline MnFe2O4 has pure cubic spinel crystal structure with average crystallite size of 11 nm. The cation distribution of these nanoparticles was estimated by X-ray analysis data. The blue shift was observed in the band gap when compared with bulk sample which is due to the quantum size effect. The absence of hysteresis for MnFe2O4 nanoparticles indicated the superparamagnetic behaviour, as expected for single domain nanoparticles. The obtained value for saturation magnetization being less than its value of bulk ones and larger pH is due to surface effects. The calculated magnetic particle size was smaller than crystallite size estimated from the XRD results; which indicate the presence of dead layer on particle surface.