Microwave Processing and Magnetic Characterization of ZnO:Co Samples Synthesized in Single Mode (H 011 ) Resonant Cavity Subhash C. Kashyap*, Charu Lata Dube , D. C. Dube Department of Physics, Indian Institute of Technology Delhi, Hauz Khas, New Delhi-110016, India Corresponding author: skashyap@physics.iitd.ac.in Abstract: In the present work, polycrystalline samples of ZnO doped with cobalt have been prepared in a H 011 single mode cylindrical microwave (MW) resonant cavity at a temperature of nearly 1000 o C in 40 minutes. The x-ray diffractograms of the microwave processed samples establish the incorporation of cobalt in ZnO lattice in the MW processed samples. Room temperature magnetic (M-H) measurements of the starting mixture and Co-substituted samples indicate that the nature of magnetic interaction changes on incorporation of Co into ZnO lattice. Keywords: Microwave processing, Zinc oxide, Ferromagnetism Introduction: Microwave (MW) processing of metals, semiconductors and ceramics has opened a new vista of research due to its unique advantages, possibilities and industrial applications [1, 2]. Microwave heating is volumetric, rapid and energy efficient technique for sintering, calcinations and/or phase- transformation [3, 4] the technique is material-property as well as - structure sensitive [5]. In some cases the interaction of MW with materials leads to formation of new phases also [4]. Transition metal doped oxide semiconductors (ZnO, TiO 2 and SnO 2 ), exhibiting room temperature ferromagnetism (RTFM) are potential candidates for spintronic devices. Transition metal (Co) doped ZnO has been prepared in nanocrystalline [6] and thin film [7, 8] forms by chemical coprecipitation and spray pyrolysis techniques, respectively. These samples have revealed room temperature ferromagnetism with a magnetization value of nearly