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Study of Structural, Electrical and Magnetic Properties of Manganese Doped Cobalt Ferrite Nanoparticles with Non-stoichiometric Composition



Author(s)

M. Z. Ahsan1,2 and F. A. Khan2

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DOI:10.17265/2159-5348/2017.06.005

1. Department of Physics, Military Institute of Science and Technology (MIST), Dhaka-1216, Bangladesh 2. Department of Physics, Bangladesh University of Engineering and Technology (BUET), Dhaka-1000, Bangladesh

The nanoparticles of Co_1+xMn_xFe_2-xO₄ (0≤x≤0.5) ferrite system are synthesized by solid-state reaction route using planetary ball milling technique to investigate structural, electrical and magnetic properties. The X-ray diffraction patterns confirm the inverse spinel structure with residual oxide phases. Three distinct regions of frequency response on dielectric constant are observed Co_1.25Mn_0.5Fe_1.75O₄ as determined by the Wayne Kerr Impedance Analyzer. The first two regions of frequency response 1.13-4.5 MHz and 4.5-6.5 MHz exhibit the normal behavior but the last region 6.5-10.5 MHz indicates its anomalous behavior due to concurrent contribution of O^2-, Fe³⁺, Co²⁺ and Mn³⁺ ions in the relaxation process for sintering effects (sintered at 700 °C). This anomalous behavior is found to be pronounced and significant for the sample of composition Co_1.25Mn_0.25Fe_1.75O₄, which may be suitable to be used in the frequency band filter over wide range of frequencies. The single peak of imaginary part of dielectric constant (ε") indicates that the conduction process in this sample is due to the grain boundary resistance. The pronounced increase of capacitance (C) as observed from 100 °C to 125 °C in temperature dependent measurement (30-125 °C) is expected to cause from the change of polarization across the grain boundary due to redistribution of ions by the thermal agitation. The variation of resistance (R) with temperature (30-125 °C) is found to exhibit semiconducting behavior that resulted from the p-type carriers (Co²⁺/Co³⁺). A significant increase of Z from 105 °C with the increase of temperature indicates the signature of phase transition from ferrimagnetic-to-ferromagnetic, which may be ascribed to the increase of Co content. The appearance of the single semicircular arc in the Cole-Cole plot may be attributed to the contribution of grain boundary resistance and correspond to the parallel equivalent circuit of resistor-capacitor (R-C) combination with single relaxation time. Saturation magnetization of Co_1.25Mn_0.25Fe_1.75O₄ and Co_1.375Mn_0.375Fe_1.625O₄ is found to be greater than the literature value (61.5 emu/g) of un-doped cobalt ferrite in the measurement of their initial magnetization using Lakeshore vibrating sample magnetometer. The negative real part of AC permeability of Co_1.5Mn_0.5Fe_1.5O₄ signifies the diamagnetic behavior in the frequency range 0.13-25.2 MHz and expected to cause from the formation of magnetic dipoles opposite to the applied field due to Mn²⁺ in the B site. The samples are expected to be suitable for dielectric heating and high frequency applications.

Cobalt ferrite, dielectric constant, capacitance, resistance, impedance, cole-cole plot, magnetization.