Influence of transition metal ions (Cu, Cr) on the structural and magnetic properties of Mn-Zn ferrites

Abstract

Three series of Mn-Zn based ferrites have been prepared for investigation of the influence of transition metal ions (Cu, Cr) on their structural and magnetic properties. The three series of ferrite compositions are i) Mn0.50-xZn0.50CuxFe2O4 where the value x ranges from 0.0-0.3 at a step of 0.1, ii) Mn0.50Zn0.50-xCuxFe2O4 where the value x ranges from 0.00-0.50 at a step of 0.05 and iii) Mn0.50Zn0.50CrxFe2-xO4 where the value x ranges from 0.00-1.0 at a step of 0.10. Samples of all chemical compositions have been prepared by auto combustion method. Pellet- and toroid-shaped samples prepared from each composition and sintered at different sintering temperatures in air for 5 hours. Structural and surface morphology are carried out by X-ray diffraction (XRD) and optical microscopy, respectively. The magnetic properties of these ferrites such as complex permeability and temperature dependent permeability have been measured by a Wayne Kerr Impedance Analyzer. DC magnetization and B-H loops measurements at room temperature by SQUID magnetometer and an Automatic Magnetic Hysteresis Graph Tracer respectively. The XRD analyses revealed that all the samples of the three series crystallize in single phase and formed cubic spinel structure. There is a decrease of lattice constants due to Cu2+ and Cr3+ ion substitutions. The lattice constants of Mn0.50Zn0.50-xCuxFe2O4 and Mn0.50-xZn0.50CuxFe2O4 decrease linearly with Cu2+ ion obeying Vegard’s law. Theoretical density of these compositions is slightly greater than that of their bulk densities due to existence of some pores in the bulk sample. Bulk density depends on sintering temperature. It increases up to some optimum 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 uniformity in average grain size has significant influence on the magnetic properties such as permeability and magnetization. The microstructural study shows that both the sintering temperatures and the cations substitutions have great influence on the average grain size. The average grain sizes of all the samples increase with increasing Cu2+ ion substitution in Mn0.50-xZn0.50CuxFe2O4, decrease with Cr3+ ion substitution in Mn0.50Zn0.50CrxFe2-xO4. The average grain size increases with Cu2+ ion substitution in Mn0.50Zn0.50-xCuxFe2O4 up to x=0.20 thereafter it decreases. A significant change in initial permeability has been found (increase or decrease) by the Cu The average grain sizes of all the samples of the three series increases with increase in sintering temperatures. 2+ and Cr3+ ion substitution in Mn0.50-xZn0.50CuxFe2O4, Mn0.50Zn0.50- xCuxFe2O4 and Mn0.50Zn0.50CrxFe2-xO4. The initial permeability of all the samples increases with increasing Cu2+ ion substitution in Mn0.50-xZn0.50CuxFe2O4, decreases with Cr3+ ion substitution in Mn0.50Zn0.50CrxFe2-xO4. The initial permeability increases with Cu2+ ion substitution in Mn0.50Zn0.50-xCuxFe2O4 up to x=0.20 thereafter it decreases. The highest initial permeability (1061) is observed for x = 0.3 in Mn0.50- xZn0.50CuxFe2O4 sintered at 1300 °C which is greatly enhanced from 258 to 1061(∼400%) compared to parent composition. The highest relative quality factor (12800) has been found for the sample Mn0.50Zn0.40Cr0.10Fe2O4 sintered at 1300 °C. The temperature dependent initial permeability of all the samples increases with increasing Cu2+ ion substitution in Mn0.50-xZn0.50CuxFe2O4 and Mn0.50Zn0.50-xCuxFe2O4 where as it decreases with Cr3+ ion substitution in Mn0.50Zn0.50CrxFe2-xO4. The saturation magnetization (Ms), coercivity (Hc) and remanent induction (Br) have been calculated from the M-H and B-H loops at room temperature. Ms increases with the increase in Cu2+ in Mn0.50-xZn0.50CuxFe2O4 and decreases for increasing Cr3+ content in Mn0.50Zn0.50CrxFe2-xO4 but it increases up to x = 0.20 in Mn0.50Zn0.50CrxFe2-xO4 and for further increase in Cu2+ content it decreases. The Hc decreases with increasing Cu2+ content in Mn0.50-xZn0.50CuxFe2O4 whereas there is an increase of Ms and Br, Hc increases with Cr3+ in Mn0.50Zn0.50CrxFe2-xO4 due to decrease of anisotropy constant.