Investigation of structural and magnetic properties of lanthanum substituted Ni-Mg-Cu-Zn ferrites

Abstract

PolycrystalHne Nio IMg,:usCuowlno5oFe2_xLax04 (with x = 0.00, 0,025, 0.050 and 0.075) were prepared by conventional solid state reaction technique. Pellet and toroid shaped samples were preJlllred from each composition and were sintered at various temperatures (T,) in air for 5 hours. The influences of microstructure, La substitution in place of Fe and T, on the complex permeability of above mentioned samples are discllssed. A possible correlation among T" C()mplex permeability and density is also discussed. The Neel temperature (TN) of the samples is measllred from the temperature dependent real part of initial permeability (11:). X-ray diffraction patterns of the samples show the formation of cubic spinel structure. Lattice parameter increases with increasing La substitution. This result is explained with the help of ionic radii of snbstituted cations. The average grain size slightly decreases with increasing La substitution whereas increases with increasing T,. Theoretical density (P'h) and bulk density (Ps) both increase with increasing La C()nten!. This can be explained on the basis of atomic weight. The PB increases with increasing T, np to 1200°C then decreases for a further increase of T. up to 1250°C. On the other hand porosity has the opposite trend. The p; decreases with increasing La substitution probably due to the decrease of average grain size. It is also ObselVedthat P,' increases with increa5ing T, for all ferrites up to 1200°C then decrea5es for sample sintered at 1250°C. It is expected that there might have a correlation between PH and permeability. The J.I: remains fairly constant in the frequency range up to 10 kHz or greater for parent composition and I MHz or greater for La doped compositions. The imaginary pari of initial permeability starts raising beyond this freqllency which is an indication of dispersion or resonance. At high frequency, the loss factor of all La doped compositions is lower than parent composition and decreases with increasing La substitution. The relative quality factor is found to be maximwn in Nio,12Mgo,l!CUo,2(lZnQ.5oFeL915U1<JsGin7te5r0e4d at 1250°c. The TN was found to decreases with La substitution up to x=0.050 beyond which TN increases. The decrease of the TN is dlle to the weakening of the A-B exchange interaction and vice versa The magnetization of all samples increases linearly with increasing applied magnetic field up to 0.1 T. Beyond this fieid, magnetization increases slowly and then saturation occurs. Saturation magnetization decreases with increasing La substillltion.