Investigation of structural and magnetic properties of Gd substituted Mn-Ni-Zn ferrites

Abstract

Polycrystalline Mn0.5Ni0.1Zn0.4Fe2-xGdxO4 (x = 0.0, 0.015, 0.03, 0.06, and 0.1) ferrites are prepared by standard solid state reaction technique. The samples prepared from each composition are sintered at various temperatures (1150, 1200, 1250, 1300, and 1350 ºC) in air for 3 hours. Structural, surface morphology and compositional analysis are characterized by X-ray diffraction (XRD), Scanning Electron Microscopy (SEM) and Energy Dispersive X-ray (EDX) spectroscopy, respectively. The magnetic properties of these ferrites such as frequency and temperature dependent complex initial permeability are measured by Wayne Kerr Impedance Analyzer and the DC magnetizations as a function of applied magnetic field are performed by Vibrating Sample Magnetometer (VSM). The frequency dependent dielectric properties are also studied by Impedance Analyzer. The XRD patterns confirm the formation of spinel structure with the appearance of very few impurity peaks. The exact lattice parameter, ao, decreases with the Gd content up to x = 0.03 then it increases with the increase of Gd content. The bulk density decreases and the corresponding porosity of the samples increases with the increase of Gd content, but they show opposite trend with the increase of sintering temperature. The average grain size goes on decreasing with the Gd content and increases with the sintering temperatures. EDX analysis reveals that the concentration of Gd element in the grain boundaries is more than that in the grains. The real part of initial permeability is found to decrease considerably with the substitution of Gd content and increases gradually with increasing sintering temperature. Highest value of initial permeability (μi / = 315) is observed for Mn0.5Ni0.1Zn0.4Fe1.97Gd0.03O4 sample sintered at 1350 ºC. The resonance frequency for all the samples increases with the increase of Gd content, which is found within the range of 5.8~36.3MHz. The magnetic loss factor for the Gd substituted samples is comparably less than the un-substituted samples at frequency greater than 106Hz. The Néel temperature, TN, increases considerably with increasing Gd content (about 200 ºC for the sample with x = 0.03 higher than that with x = 0). For x > 0.03, TN decreases but its value is still much higher than that of the un-substituted sample. The variation of magnetization with applied magnetic field confirms that all compositions show the behavior of soft ferrites at room temperature. It is found that the saturation magnetization slightly increases for x = 0.015 and then it decreases with increasing Gd-content. The dielectric loss tangent, tanδ, is considerably lower than that of the un-substituted sample at frequency greater than 104Hz, which can be the potential applications of these materials in high-frequency microwave devices.