Magnetic and Mössbauer Studies of Bare and Encapsulated Nanoparticles of [(Co0.2Mn0.3Zn0.5Fe2O4)(1-x) (ZnO/PVA)x (x = 0 and 0.30)

Abstract

Nanoparticles of Co substituted Mn–Zn-ferrite (Co0.2Mn0.3Zn0.5Fe2O4) were prepared by coprecipitation method. Co substitution in Mn–Zn-ferrite was considered to obtain the superparamagnetic (SPM) behavior at room temperature (RT) in bigger-sized particles as well as to enhance the saturation magnetization. To modulate the dipolar interaction, magnetic nanoparticles were coated with nonmagnetic matrices of ZnO and polyvinyl alcohol. The formation of the mixed spinel phase of different heat-treated samples was confirmed by X-ray diffractograms (XRD). The sizes of nanocrystallites obtained from the Debye–Scherrer formula are in the range of 10–51 nm. The average sizes of nanoparticles and their distribution, morphology, crystallographic phase, etc., of some selected samples were determined from the results of high-resolution transmission electron microscopy (HRTEM). The average particle sizes and their distributions of all the samples were obtained from the dynamic light scattering measurement. Hysteresis loops, magnetization versus field curve, zero-field cooled, and field-cooled magnetization versus temperature curves of some samples were recorded by superconducting quantum interference device (SQUID) magnetometer. The magneto-crystalline anisotropy, average particle size, and its distribution, etc., of the bare and coated samples were calculated from the analysis of the static magnetic data and the results are in good agreement with those obtained from XRD and HRTEM observations. Dynamic hysteresis loops at different frequencies and Mössbauer spectra of the samples were recorded at RT that indicate the presence of SPM relaxation of the nanoparticles.