Magnesium and yttrium doped superparamagnetic manganese ferrite nanoparticles for magnetic and microwave applications

Magnesium and yttrium doped manganese ferrite nanoparticles based on chemical formula MgxMn1-xYxFe2-xO4 (x = 0.0, 0.05, 0.10, 0.15) have been prepared by chemical coprecipitation technique and calcined to 600 C. Thereafter, structural, morphological, optical, magnetic and dielectric investigations were performed. X-ray diffraction (XRD) suggests that the grown composition is cubic spinel. Parameters like crystallite size, lattice parameter, unit cell volume and theoretical density were determined. The crystallite size has been found to decrease from 47 nm to 37 nm for x = 0.0-0.15 respectively. Scanning electron microscope (SEM) equipped with energy dispersive X-ray (EDAX) has been used to investigate the morphology and elemental analysis. The optical band gap calculated using Kubelk-Munk (K-M) method increases from 1.84 eV for x = 0 to 2.35 eV for x = 0.15. The spin characteristics investigated through electron paramagnetic resonance (EPR) spectroscopy gives various parameters like g-value, resonance field (H-r), peak to peak line width (H-pp) and relaxation time (tau(2)). The value of g is determined and comes out to be 2.086, 2.047, 2.043 and 2.039 for x = 0.0, 0.05, 0.10 and 0.15 respectively. The hysteresis curves obtained using vibrating sample magnetometer (VSM) shows ferrimagnetic behavior of composition. Saturation magnetization (M-s), retentivity (M-r), coercivity (H-c), remenance ratio (M-r/M-s), anisotropy constant (K-1) and Bohr magneton number (n) were determined. The value of saturation magnetization decreases from 18.12 emu/g to 7.4 emu/g when the doping concentration increases from x = 0.0 to 0.15. M-r and H-c values are small representing the superparamagnetism. M-r/M-s suggests the single domain structure. The dielectric constant shows frequency dispersion which is typical in spinel ferrites. The value of dielectric constant is high in pure manganese ferrite and decreases with increase in Mg2+ and Y3+ content e.g., at 2.5 kHz the value of dielectric constant is 62 for x = 0.0 and 22 for x = 0.15.