Influence of various cations substitution on structural and magnetic properties of some Co-based spinel ferrites

Abstract

In this research three series of ferrites have been prepared for investigation of the effect of substitution of divalent and trivalent cations in various Co-based ferrites. The three series are Co0.5-xMnxZn0.5Fe2O4, Co0.5Zn0.5CrxFe2-xO4 and Co0.5Cu0.5CrxFe2-xO4, where the value of x ranges from 0 to 0.4. All chemical compositions have been prepared by a conventional solid state reaction technique. Pellet- and toroid-shaped samples are prepared from each composition and are sintered at different sintering temperatures in air for 5 hours. Structural and surface morphology are carried out by X-ray diffraction and optical microscopy, respectively. The magnetic properties of these ferrites such as complex permeability and temperature dependent permeability have been measured by Wayne Kerr Impedance Analyzer and DC magnetizations by SQUID magnetometer. All compositions are single phase and formed spinel structure. There is an increase or decrease of lattice constants due to Mn and Cr substitutions. No noticeable change in lattice constant for different sintering temperatures. Theoretical density of these compositions is slightly greater than that of their bulk density due to existence of some pores in the bulk sample. Bulk density depends on sintering temperature. It increases up to some optimum sintering temperature (depending on composition) due to uniform grain growth and thereafter it is decreased due to discontinuous grain growth. Porosity of these compositions follows the opposite trend. The microstructural study shows that both the sintering temperatures and the cations substitutions have great influence on the average grain size. The average grain size increases with increasing Mn substitution in Co0.5-xMnxZn0.5Fe2O4, decreases with Cr substitution in Co0.5Zn0.5CrxFe2-xO4, and increases up to x = 0.2 and thereafter decreases with Cr substitution in Co0.5Cu0.5CrxFe2-xO4. A significant change in initial permeability (increase/decrease) has been found by the Mn/Cr ion substitution in Co0.5-xMnxZn0.5Fe2O4/Co0.5Zn0.5CrxFe2-xO4, whereas it is increased up to x = 0.2 and is decreased for x > 0.2 for Cr substitution in Co0.5Cu0.5CrxFe2-xO4. The highest initial permeability (137) is observed for x = 0.4 sintered at 1573 K in Co0.5-xMnxZn0.5Fe2O4., which is double of the parent composition. The highest relative quality factor (2522) is obtained for the sample Co0.2Mn0.3Zn0.5Fe2O4 sintered at 1523 K. The saturation magnetization, coercivity and remanent magnetization have been calculated from the M-H loops at 300 and 10 K. The saturation magnetization increases for x = 0.1 and decreases for increasing both Mn and Cr content in Co0.5-xMnxZn0.5Fe2O4 and Co0.5Cu0.5CrxFe2-xO4. It decreases with increasing Cr content in Co0.5Zn0.5CrxFe2-xO4. The coercivity decreases with increasing Mn content in Co0.5-xMnxZn0.5Fe2O4, increases with Cr in Co0.5Zn0.5CrxFe2-xO4 due to decrease or increase of anisotropy constant while it increases up to x = 0.2 and decreases for higher Cr concentration in Co0.5Cu0.5CrxFe2-xO4. A reentrant spin glass behavior is confirmed for both Co0.5-xMnxZn0.5Fe2O4 and Co0.5Zn0.5CrxFe2-xO4 compositions at low temperature. The Néel temperature is found to decrease with increasing Mn/Cr content in above mentioned three series due to weakening the super-exchange interaction. The Néel temperature of Cr substitution in Co0.5Cu0.5CrxFe2-xO4 has been found quite high in comparison to other Mn and Cr substitution in Co0.5Cu0.5CrxFe2-xO4 and Co0.5-xMnxZn0.5Fe2O4. The DC resistivity is found to increase with increasing Mn content in Co0.5-xMnxZn0.5Fe2O4 and Cr content in Co0.5Zn0.5CrxFe2-xO4. The AC electrical properties of Co0.5Cu0.5CrxFe2-xO4 were measured as a function of frequency in the range of 20 Hz to 120 MHz. An increasing dielectric constant and dielectric loss with increasing Cr content up to x = 0.2 are found and above x > 0, they are found to decrease. On the other hand, AC resistivity follows the opposite trend.