Cation distribution and magnetic properties of Zn^sup 2+^ substituted MnFe^sub 2^O^sub 4^ nanoparticles

Mn-Zn ferrite nanoparticles of the composition Mn1-xZnxFe2O4 (x = 0, 0.2, 0.4, 0.6, 0.8 and 1) have been synthesized by a low temperature chemical co-precipitation method. The X-ray diffraction pattern confirms the synthesis of single crystalline phase of Mn-Zn ferrite nanoparticles. Crystallite size is of the order of 4-8 nm for all these samples. The lattice parameter decreases from 8.5075 to 8.4281 Å with increase in zinc concentration. Formation of the spinel Mn-Zn ferrite was also supported by Fourier Transform Infrared Spectroscopy. Transmission electron microscopy was used to confirm the nanocrystalline nature of the samples. The magnetic measurements show superparamagnetic nature of the samples with zero remanence and coercivity. The saturation magnetization increases with increase in zinc concentration, reaches maximum at x = 0.4 and decreases for further increase in zinc concentration. The variation in saturation magnetization can be correlated to the modifications in cation distribution as a result of replacement of Mn-ion by Zn-ion thereby modifying the superexchange interaction between the A and B sublattices. Electron paramagnetic resonance (EPR) studies revealed that superexchange interaction between magnetic ions with oxygen ion and magnetic dipole interactions among nanoparticles are the two main factors, which determine EPR resonance parameters. The Curie temperature for MnFe2O4 nanoparticles is 394 °C and decreases to 95 °C for x = 0.6. Thus the relative composition of Mn and Zn can tune the Curie temperature of Mn-Zn ferrite nanoparticles which is very important for preparing the temperature sensitive ferrofluid that has the applications in the thermal management of the electronic systems.