Magnetic properties of Ni-Zn ferrites prepared by microwave sintering method M. Penchal Reddy & W. Madhuri & N. Ramamanohar Reddy & K. V. Siva Kumar & V. R. K. Murthy & R. Ramakrishna Reddy Received: 28 November 2009 / Accepted: 22 November 2011 / Published online: 2 December 2011 # Springer Science+Business Media, LLC 2011 Abstract The effect of zinc ion substitution for nickel on structural and magnetic properties of NiZn ferrites is reported. The spinel ferrite system Ni 1-x Zn x Fe 2 O 4 with x 0 0.2, 0.3, 0.4 and 0.5 was prepared by microwave sintering method. The uniaxially pressed samples were sintered at various temperatures such as 900°C, 1000°C and 1100°C for 30 min. X-ray diffraction patterns of the samples indicate the formation of single-phase cubic spinel structure. SEM micrographs show that grain size increases with increasing zinc content and sintering temperature. The elemental composition of these ferrites was analyzed by EDS. Lattice constant increases with increase in zinc content, obeying Vegard’ s law. The effect of composition and sintering temperature on initial permeability as the function of frequency and temperature was studied. The initial permeability of NiZn ferrite increases great- ly with increasing Zn content and sintering temperature. The dependence of initial permeability with respect to temperature shows the decrease in the Curie point with increase in zinc content, is the normal behavior of ferrites. The relative loss factor ðtan d μ i = Þ of the order of 10 -2 to 10 -5 in the frequency range from 100 Hz to 1 MHz indicates that the prepared ferrites have relatively high purity. Keywords Ceramics . X-ray diffraction . Microstructure . Magnetic properties 1 Introduction Ceramic ferrites are magnetic materials composed of selected oxides with iron oxides. The most common commercial soft magnetic materials are spinel ferrites, Ni-Zn and Mn-Zn ferrites having the general structure AB 2 O 4 . The Ni-Zn ferrite is preferred for low and higher frequency applications generally for power transformers, power inductors, micro wave devices, read and write heads for high speed digital tape, etc. because of their high resistivity, low losses, mechanical hardness, high Curie temperature and chemical stability [1–6]. The magnetic properties of ferrites are highly dependent on chemical composition, crystal structure, grain size and porosity. It is a well-known fact that the properties of ferrite materials are strongly influenced by the material’ s composition and microstructure. Due to their various technological applications, NiZn ferrites have attracted recently considerable research interest. The ferrites, in powder, pillets or in thin film forms, were prepared by the high-temperature solid state reaction method [7], coprecipitaion [8], sol–gel method [9], pulsed laser deposi- tion [10], high-energy ball milling [11], hydrothermal tech- nique [12], and flash combustion technique [13]. Several workers have successfully prepared Ni-Zn ferrites by the microwave sintering technique [14–18]. Use of microwave energy for synthesis and processing of materials is an exciting new field in material science with M. P. Reddy (*) : K. V. S. Kumar : R. R. Reddy Department of Physics, Ceramic Composite Materials Laboratory, Sri Krishnadevaraya University, Anantapur 515 055, India e-mail: penchu321@gmail.com W. Madhuri School of Advanced Sciences, VIT University, Vellore 632014, India N. R. Reddy Department of Materials Science and Nanotechnology, Yogi Vemana University, Kadapa 516 227, India V. R. K. Murthy Microwave laboratory, Indian Institute of Science, Chennai 600 036, India J Electroceram (2012) 28:1–9 DOI 10.1007/s10832-011-9670-7