RESEARCH PAPER Enhancement of electrical conductivity and dielectric constant in Sn-doped nanocrystlline CoFe 2 O 4 Atta ur Rahman • Muhammad Aftab Rafiq • Masood ul Hasan • Maaz Khan • Shafqat Karim • Sung Oh Cho Received: 28 January 2013 / Accepted: 6 May 2013 / Published online: 15 May 2013 Ó Springer Science+Business Media Dordrecht 2013 Abstract We have investigated the dielectric con- stant and capacitance of pure and tin-doped cobalt ferrite nanoparticles. The nanoparticles with spinel structure were synthesized by chemical co-precipita- tion method. The average particle size of the samples was 20 ± 2 nm. Room temperature impedance spec- troscopy of the nanoparticles was performed in the frequency range of 100 Hz–2 MHz. The conductivity and dielectric response of the nanoparticles were found to increase with tin doping (20 % by atoms) in cobalt ferrite nanoparticles. The observed value of high-dielectric response at low frequencies has been attributed to the presence of grain boundaries in these nanoparticles. Keywords Ferrites  Conductivity  Coprecipitation  Dielectric  Polarization Introduction Spinel ferrites fall in the category of semiconductor ceramics and have high dielectric constant that are of considerable interest due to their potential applications in the future technology. Cobalt ferrite is used in magnetic, magneto-optical recording, electromag- netic, and spintronics devices (Zhao et al. 2008). The electrical properties strongly depend on the composi- tion, annealing conditions, grain sizes, and dopant materials (George et al. 2007; Shaikh et al. 2005). Dielectric properties of cobalt ferrite have been studied with various dopant materials and concentra- tions (Shinde and Jadhav 1998; Farea et al. 2008). In most of these studies, a decrease of dielectric constant and conductivity of the materials with dopant con- centration has been reported. Contrary to the previous analyses, we report an increasing behavior of conduc- tivity and dielectric constant with 20 % doping of tin in cobalt ferrite nanoparticles. The materials with high-dielectric constants (C10 3 ) have become immense interest for the miniaturized memory devices that are based on the capacitive components or energy storage principles (Homes et al. 2001, 2003; Krohns et al. 2009). The high values of dielectric constant A. u. Rahman  M. A. Rafiq  M. u. Hasan Micro and Nano Devices Group, Department of Metallurgy and Materials Engineering, Pakistan Institute of Engineering and Applied Sciences, P.O. Nilore, Islamabad, Pakistan e-mail: attaurrahman555@yahoo.com M. A. Rafiq e-mail: fac221@pieas.edu.pk M. Khan (&)  S. Karim Nanomaterials Research Group, Physics Division, PINSTECH, P.O. Nilore, Islamabad 45650, Pakistan e-mail: maaz@impcas.ac.cn S. O. Cho Department of Nuclear and Quantum Engineering, Korea Advanced Institute of Science and Technology (KAIST), 373-1 Guseong, Yuseong, Daejeon 305-701, Republic of Korea 123 J Nanopart Res (2013) 15:1703 DOI 10.1007/s11051-013-1703-5