Comparison studies of electrical and magnetic behavior of Li-Cd ferrite

Abstract

In the past few years many physicists and chemists have studied the electrical and magnetic properties of polycrystalline ferrites in view of their many applications due to their large magnetic permeability and very high dielectric constant at relatively low frequency. The manufacture of most microwave devices depends mainly on such ferrites where their properties are governed according to the preparation conditions. The high conductivity grains which are formed in polycrystalline ferrites make them of great importance and the material behaves as an inhomogeneous dielectric. Most of the spinel ferrites are of technical importance and they find intensive applications especially at microwave frequencies. In particular, mixed systems containing Zn or Cd have received much attention in the past few years [1–4] where the saturation magnetization of these systems increases linearly with the diamagnetic ion content and then decreases after certain limits. Since many properties of ferrites are strongly dependent on their exact chemical composition and microscopic physical structure, the methods of preparation are of great importance. It was found by M. A. Amer [5] that the hyper fine parameters of the tetrahedral and octahedral sites are determined as a function of the composition. The magnetic susceptibility is used to discuss the behavior of cations and anions in A (tetrahedral) and B (octahedral) sites respectively. The porosity of the samples which is a function of preparation conditions affects directly the magnetic and electrical properties [6]. In some ferrites such as Ni-Zn ferrite [7], the initial magnetic permeability of a pore-free sample was independent of the grain size and the number of pores in the coarse-grained sample was less than that in the fine grained one, but the pores were of a larger size. Recently it was found by many authors [6–8] that there is a strong correlation between the magnetic and electric properties of ferrites. The present work is a part of more extensive program dealing with the effect of electric and magnetic fields on dielectric and magnetic properties respectively for Li0.5−x/2Cdx Fe2.5−x/2 O4; 0.2≤ x ≤ 0.8. Analar grade Li oxide, Cd oxide and Fe2O3 were used as starting material for preparing the samples Li0.5−x/2Cdx Fe2.5−x/2 O4; 0.2≤ x ≤ 0.8. The standard ceramic technique [9] was used in which molar ratios of Li2O, CdO and Fe2O3 [PDH] were mixed in the stoichiometric ratio and then ground to a very fine powder using an agate mortar for 4 h. After that the samples were transferred to an electric shaker for another 4 h. The samples were compressed into pellet form with a diameter of 10 mm and thickness 2.5 mm under a pressure of 1.5× 107 N/m2. Presintering was carried out at 800 ◦C with a heating rate of 6 ◦C/min for 4 h and final sintering at 1200 ◦C with the same rate as above and then cooled to room temperature with cooling rate of 6 ◦C/min using a Lenton furnace (England) UAF 16/5 with micro processor to control both heating and cooling rates. X-ray diffraction patterns were recorded using a Philips PW 1730 X-ray unit with Co Kα radiation to determine the formation of the spinel structure. For measuring the electrical properties of the samples, the two surfaces of each pellet were polished, coated with silver paste and checked for good conduction. An RLC bridge (Hioki model 3530 Japan) was used to measure the dielectric properties for the investigated samples. A K-type thermocouple connected to a digital thermometer (USA) with a junction in contact with the sample was used to measure the temperature of the sample with an accuracy ±1 ◦C. The magnetic susceptibility was measured using the conventional Faraday’s method in which a very small quantity of the sample was inserted in the nonhomogeneous field (at the maximum force point). The relation between the electric dipole moments and Cd concentration as a function of absolute temperature is represented in Fig. 1 at a frequency of 100 kHz. The