Mössbauer spectroscopic and x-ray diffraction studies of structural and magnetic properties of heat-treated (Ni0.5Zn0.5)Fe2O4 nanoparticles

Because of their high electrical resistivity and high magnetic permeability, nickel–zinc ferrites are among the best soft magnetic materials for high-frequency applications. In this work, a precursor of nanostructured (Ni0.5Zn0.5)Fe2O4 was obtained by a sol–gel method modified for large quantity production. Six heat-treated samples were produced by calcining the precursor for 3 h at 450, 500, 600, 650, 700, and 1100 °C, respectively. X-ray diffraction peak width data have been used to estimate the particle sizes of the calcined samples. Room-temperature and low-temperature Fe57 Mössbauer effect experiments allowed us to determine whether the heat-treated nanoparticles are crystalline or amorphous, whether there is a superparamagnetic phase, and which calcining temperature is optimum for obtaining a large magnetic hyperfine field and a homogeneous magnetic phase. Room-temperature Mössbauer spectra revealed that the precursor is paramagnetic, while the heat-treated samples have the ferrimagnetic phase. The samples heat treated at a calcining temperature of 650 °C or higher showed no residual paramagnetic phase, indicating that 650 °C is the threshold calcining temperature for homogeneous (Ni0.5Zn0.5)Fe2O4 nanoparticles. A comparison between low-temperature and room-temperature Mössbauer spectra demonstrated that the precursor is paramagnetic, whereas the heat-treated (500 °C) sample has a component that shows superparamagnet relaxation.