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.
