M.U. Islam

STUDY OF SINTERING BEHAVIOR AND ELECTRICAL PROPERTIES OF Cu-Zn-Fe-O SYSTEM

Copper zinc ferrites (Cu1−xZnxFe2O4) with x = 0.1, 0.2, 0.3 were prepared by solid state reaction technique. The samples were presintered at 900°C for 40 to 45 hrs and finally at 950°C for 4 hrs followed by air quenching. The lattice parameter, X-ray densities (Dm), grain size, bulk densities (D) and porosity (P) were measured for each sample after successive heat treatments and the effect on the above mentioned properties was studied. Electrical resistivity of the samples after final heat treatment was measured in the temperature range of 50 to 230°C. The Arrhenius plots of these samples exhibit linear behavior from which the activation energy of the system has been derived. The room temperature resistivity after quenching from 950°C shows change of species of charge carriers that is from n-type at lower Zn concentration to p-type at higher Zn concentration.

Cation distribution and magnetic interactions in Zn-substituted CuFe2O4 ferrites

Abstract A series of Cu 1− x Zn x Fe 2 O 4 , spinel ferrites with x =0, 0.25, 0.50, 0.75 and 1.0, respectively, were prepared by standard ceramic method to study the relationship between structural parameters and concentration of the substituted non-magnetic (Zn) ion. Determination of crystal structure oxygen positional parameter and cation distribution using X-ray diffraction (XRD) and R -factor method revealed that these ferrites belong to the family of mixed or partially inverse spinels. The magnetic interaction has been calculated from ac susceptibility measurements using mutual inductance technique as a function of concentration of the substituted ions in these mixed ferrites. The dominant interaction in all ferrite samples is A–B interaction which is due to the negative values of paramagnetic Curie temperature θ (K) and the distribution of cations among A and B sites showing that the magnetic ordering is antiferromagnetic. The Curie temperature ( T c ) rises upto x =0.75 possibly due to increase in exchange interaction and magnetic moments. For x >0.75, T c decreases due to cation distribution (normal) on A and B-sites resulting in the weakening of A–B interaction due to the presence of triangular spin arrangement of Y–K type on B-sublattice.

Temperature dependent electrical resistivity of Co–Zn–Fe–O system

Abstract Cobalt zinc ferrites with composition Co 0.2 Zn 0.73 Fe 2 O 4 , Co 0.30 Zn 0.60 Fe 2 O 4 , Co 0.37 Zn 0.51 Fe 2 O 4 and Co 0.5 Zn 0.34 Fe 2 O 4 , were prepared by solid state reaction technique in a single phase form. The electrical resistivity, X-ray density, bulk density and porosity of each sample have been measured. A change of slope has been observed in the Arrhenius plots indicating the presence of two regions of activation energy.

EFFECT OF Mg2+ SUBSTITUTIONS ON THE STRUCTURAL AND MAGNETIC PROPERTIES OF Co–Mg W-TYPE HEXAGONAL FERRITE

W-type hexagonal ferrites having the formula BaCo2-xMgxFe16O27 with x = 0, 0.4, 0.8, 1.2, 1.6, 2.0 were synthesized by the chemical coprecipitation method. XRD analysis shows that the structure of all the compositions is W-type hexagonal ferrite. The c/a ratio varies from 5.48 to 5.52, consistent with the standard values. It was observed that the bulk density and X-ray density decrease whereas porosity increases with increasing concentration of Mg2+. Room temperature resistivity increases, from 103 to 107 (Ω cm) by increasing the concentration of Mg2+, due to an increased number of grain boundaries. The remanence and saturation magnetization decrease with increasing Mg2+ content while coercivity increases as the Mg2+ increases according to the relation Hc ∝ 1/r. The measured coercivity values are suitable for use in high frequency applications such as microwave absorber materials.

MAGNETIC PROPERTIES OF CO-PRECIPITATED MnZn FERRITE-SiO2 COMPOSITES

A series of composite ferrites with chemical formula (1–x)[Mn0.5Zn0.5Fe2O4]·x[SiO2](x = 0.0, 0.20, 0.30, 0.40, 0.50) were prepared by the co-precipitation technique. The samples were finally sintered at 1150°C followed by air quenching. The x-ray diffraction analysis confirms the phases precipitated out in the samples. AC magnetic susceptibility of these samples has been measured using the low field mutual inductance technique over the temperature range 298 K to 550 K at a frequency of 250 Hz. The magnetic parameters like Curie constant, C, Curie temperature, Tc, Lande splitting factor, g, effective magnetic moment, Peff, exchange integral, J/kB, and characteristic temperature, θ(K) were calculated. The reciprocal of susceptibility versus temperature curves of each sample follows the Curie Weiss behaviour above the Curie temperature. Below the Curie temperature, all the samples show the ferrimagnetic behaviour. It was concluded that the magnetic properties were enhanced by the addition of silicon as is evident by the variation of magnetic interactions J, with Si-concentration and followed subsequently by the Peff, θ(K) and Tc etc.