American Journal of Applied Sciences 4 (2): 80-84, 2007 ISSN 1546-9239 © 2007 Science Publications Corresponding Author: Noorhana Yahya, Advanced Materials Laboratory, Institute of Advanced Technology, Universiti Putra Malaysia, 43400 UPM Serdang, Malaysia 80 High Saturation Induction for Bi-Substituted Yttrium Iron Garnet Prepared Via Sol Gel Technique Noorhana Yahya and Goh Kah Hean Advanced Materials Laboratory, Institute of Advanced Technology, Universiti Putra Malaysia 43400 UPM Serdang, Malaysia Department of Physics, Faculty of Science, Universiti Putra Malaysia, 43400 UPM Serdang, Malaysia Abstract: Y 3.0-x Bi x Fe 5 O 12 samples (x = 0.2 and 0.4) were prepared via novel sol-gel and conventional solid-state techniques. The effect of bismuth in both techniques was investigated in terms of shrinkage, density, hysteresis and initial permeability. Sharp and clear diffraction XRD lines with highest peak appear at about 32° of the 2θ, for all the powders sintered at 900°C and 1250°C for both techniques. In evaluating the magnetic properties, it was observed that the saturation induction (1.1902kG) of sample prepared via sol-gel technique (Y 2.8 Bi 0.2 Fe 5 O 12 ) is more than 200% higher than sample with the same formula prepared via conventional technique. Fine grained microstructure with average grain size of about 5 µ m and higher shrinkage, about 11% were observed from the samples prepared via sol gel technique. It is concluded that samples prepared via sol gel technique appear to be an attractive route due to the possible reduction of cost of production and the enhanced magnetic and structural properties of the sample. Key words: Conventional solid state, hysteresis, initial permeability, sol gel technique, C (conventional) S (sol-gel) INTRODUCTION Ferrites may be defined as magnetic materials composed of oxide containing ferric ions as the main constituent. The term is often restricted to such materials having mineral spinel cubic crystal structure, but it is also loosely applied to magnetic oxides in general irrespective of their crystallic structure. Yttrium iron garnet (YIG) has been studied intensively by researchers for decades now. It prides itself as being one of the most well known soft ferrites hitherto. Its grandeur can be justified by its application in microwave devices such as spatial light modulators, guided wave optical isolators [1] , optical Faraday rotator [2] , phase shifters, switches and sensors [3,4] . Doped YIG were also subjected to scrutiny. The magnetic and electric properties of these YIG compounds changed slightly or drastically based on the type and quantity of dopant as well as substituent employed. Recent studies involved the work of Marysko [5] , who studied the properties of cobalt doped YIG films and the work of Xhang et al. that focused on the magneto-optical properties of Nd substituted YIG [6] . This work however deals with preparation of Bi- Y 3 Fe 5 O 12 samples using conventional, solid-state and novel, sol-gel techniques. The magnetic and structural properties of all the samples were investigated and compared. MATERIALS AND METHODS The raw materials used for the conventional technique in this project are bismuth oxide (purity: 99.98%), yttrium oxide (purity: 99.9%) and iron oxide (purity: 99.99%). For conventional technique, raw materials were wet mixed in milling machine for 16 hours to get a homogeneous mixture and subsequently, filtering, drying and pre-sintering were done at 1150 o C in air. On the other hand, stoichiometric mixtures of nitrates, comprise of iron (III) nitrate, Fe(NO 3 ) 3 .9H 2 O, bismuth (III) nitrate, Bi(NO 3 ) 3 .9H 2 O and yttrium nitrate, Y(NO 3 ) 3 .6H 2 O were weight and dissolve in an aqueous solution of citric acid for the sol-gel technique. The nitrates were dissolved by stirring them with a magnetic stirrer at 300 r.p.m at room temperature for three days. The solution was then heated up to 80°C with the same stirring rate until the gel was obtained. The gel was then dried at 110°C in an oven for another 24 hours. The dried powders were then sent for x-ray diffraction measurements to discern the reaction pathway and to study the gel to crystalline transformation. The samples were then pre-sintered at 1150°C (solid-state) and 800°C (sol-gel) in air for 5 hours. All the pre-sintered green powders were wet crushed for 6 hours using Planetary Micromill to obtain fine particles granules. The green powders were moulded to a toroidal shape using hydraulic machine at 60kN. 1.5% of PVA acted as binder and 1.5% of zinc