Study of microstructure, magnetic and gas sensing properties of porous Ni0.4+xZn0.6-xCeyFe2-yO4 magnetic nanoparticles.

Abstract

The spinel ferrite systemsNi0.4+xZn0.6􀀀 xCeyFe2􀀀 yO4 (0 ≤ x+ y ≤ 0.3) were synthesized by a modified glycolthermal technique. X-ray diffractometer (XRD) confirmed formation of single phase cubic spinel structure with average crystallite sizes 8–21 nm. The crystallite sizes were found to be in agreement with the particle sizes obtained from the high resolution transmission electron microscopy (HRTEM) indicating formation of single domain nanoparticles. Scanning electron microscopy (SEM) showed a homogeneous spread of semi-spherical nanoparticles. Brunauer-Emmett-Teller (BET) revealed specific surface area ranging between 64 and 108 m2/ g, while Barrett-Joyner-Halenda (BJH) showed the pore sizes varying between 48 and 126 nm. Cation distribution obtained from Rietveld refinement revealed all Ce3+ occupied B- sites whilst Ni2+, Zn2+, Fe3+ occupied both A and B sites. Magnetization measurements were performed using the vibration samples magnetometer (VSM). The saturation magnetization varied between 51 and 60 emu/g, while the coercivity dropped from 114 to 89Oe. The remnant magnetization varied between 3 and 12 emu/g. A correlation was observed between the saturation magnetization and the effective magnetic moments confirming cation distribution to be reliable. A strong correlation between initial susceptibility and unit cell volume was found. The crystallite sizes varied inversely with initial magnetic susceptibility. The magnetic characteristics of presented materials make them useful in high frequency device applications and has potential use as contrast agent in magnetic resonance imaging (MRI). 57Fe M¨ossbauer spectroscopy revealed the strengthening of ferromagnetic coupling. Gas sensing tests revealed a decrease in sensing response with the transition from paramagnetic state to ferromagnetic state. The Ni0.4Zn0.6Fe2O4 sample showed the best sensing response to SO2 at 100 ◦C compared to CO gas. However, at 150 ◦C the sample was more sensitive to CO gas than SO2 gas.