Dielectric and magnetic properties of sol–gel derived mullite-iron nanocomposite Debasis Roy & Biswajoy Bagchi & Sukhen Das & Papiya Nandy Received: 23 August 2011 / Accepted: 2 April 2012 / Published online: 26 April 2012 # Springer Science+Business Media, LLC 2012 Abstract Synthesis of highly crystallized mullite has been achieved at a temperature of 1000°C by sol–gel technique in presence of iron ions of different concentrations. XRD, FTIR spectroscopy, FESEM, LCR meter and HyMDC, Hys- teresis measurement instrument, characterized samples. Mullite formation was found to depend on the concentration of the ions. The dielectric properties (dielectric constant, tangent loss and a.c. conductivity) of the composites have been measured, their variation with increasing frequency and concentration of the doped metal was investigated, and magnetic behavior was observed from the hysteresis loops. All the experimentations were performed at the room temperature. The composite showed a minimum dielectric constant of 3.26 at 0.002(M) concentration of iron at 1.5 MHz and the magnetic properties of nanocomposites suggest that the iron nanoparticles show hysteresis loop in 0.10 M, 0.15 M and 0.20 M , hence acts like typical paramagnetic materials as is the case for other iron-doped ferrisilicates. Keywords Mullite . Sol–gel . XRD . Dielectric properties . Magnetic property 1 Introduction Microelectronics industry is continuously trying to develop processes that are more advanced and which lead to fore- casting transistor density, chip complexity, and operating speed or frequency for future technological developments. The main challenge is to carry electric power and to distrib- ute the clock signals that control the timing and synchronize the operation. This challenge extends beyond the material properties and technology and also involves system archi- tecture. The propagation velocity of electromagnetic waves will become increasingly important due to their unyielding constraints on interconnect delay. Interconnect technology is the main factor for signal delay. The impact of delay will undoubtedly increase as we move into the nanometer re- gion. Now the materials with low-k dielectrics will be suit- able for lowering signal delay. Hence, they can be used in high-speed circuits as well as in high package density substrate [1–4]. Mullite based composites have been increasingly gaining importance for high frequency circuit packaging and elec- tronic substrate application due to their low dielectric con- stant (~6) and low thermal expansion coefficient. Earlier, alumina was used as substrate but the comparatively high dielectric constant (~9) increases the signal transmission delay time (t d ).The dielectric constant of the medium deter- mines the speed of the signal passing through it. The signal transmission delay time (t d ) is given by t d 0 (є r *s)1/2/c, where, є r is the dielectric constant of the medium, s is the signal path length and c is the velocity of light. For high performance circuits ‘t d ’ should be as low as possible. Hence mullite with its low dielectric constant is most suit- able for such application [2–7]. Nanocomposite materials containing magnetic particles are very interesting in many applications since they exhibit new exciting electronic, magnetic and optical properties. Several reports have been published dealing with synthesis of mullite composites in presence of various ‘mineralizers’ D. Roy : B. Bagchi : S. Das (*) : P. Nandy Physics Department, Jadavpur University, Kolkata 700 032, India e-mail: debasis35@yahoo.co.in J Electroceram (2012) 28:261–267 DOI 10.1007/s10832-012-9725-4