Magneto-electric characterization of x (Na 0.5 K 0.5 ) 0.94 Li 0.06 NbO 3 - (1-x) NiFe 2 O 4 composite ceramics R. Rakhikrishna 1 & Johney Isaac 1 & Jacob Philip 2 Received: 8 October 2014 /Accepted: 26 October 2015 # Springer Science+Business Media New York 2015 Abstract Lead free magneto-electric composites of Sodium Potassium Lithium Niobate-Nickel Ferrite (NKLN-NFO) with different molar weight percent of NKLN are prepared by solid state reaction involving co-precipitation and sintering. Four different compositions of x NKLN-(1-x) NFO have been selected to perform systematic studies on their magneto-electric properties. The dielectric constant of dense samples is measured as functions of frequency, temperature and external magnetic field. Dielectric constant is found to decrease after poling, and show resonance/relaxation peaks in dielectric properties at certain frequencies. AC conductivity is determined to understand the mechanism of conductivity. Changes in dielectric constant with applied magnetic field (or magneto-dielectric effect) are also reported. The magneto- electric coefficient for the composition with x =0.8 is found to be 2.32×10 -2 V/cm-Oe while with x =0.85 it is 2.43×10 -2 V/cm-Oe. These are the highest values reported so far for a lead free composite material prepared by normal solid state reaction cum sintering route. We find that x NKLN- (1-x) NFO exhibits sufficiently high room temperature magneto-electric coefficient suitable for applications compared to other lead free composites prepared by solid state route. Keywords Sodium Potassium Lithium Niobate-Nickel ferrite . Magneto-electric coupling . Magneto-electric composites . Magneto-dielectric effect 1 Introduction Multiferroic magneto-electric materials possess great potential for a multitude of applications, such as magnetic field sensors, microelectronic and spintronic devices, magnetic memory el- ements etc. In general, a multiferroic material performs more than one task at a time. In magneto-electric materials electric polarization can be controlled by magnetic field and magneti- zation by electric field. Technological aspirations of miniatur- ization of devices enhance the interest in such materials [1]. Though magneto-electric effect was first observed in a single phase material [2], it was found unsuitable for any device application due to the weak magneto-electric effect at room temperature. To overcome this limitation artificial composites comprising of mixtures of piezoelectric and magnetostrictive phases have been proposed. Magneto-electric composites have the advantages of greater design flexibility and multi- functionality at room temperature than any single phase ma- terial [3]. The magneto-electric coupling factor is an important parameter that determines the efficiency and usefulness of these materials for any magneto-electric device application. Magneto-electric coupling arises either directly between elec- tric and magnetic ferroic orders or indirectly via strain. In strain mediated systems the coupling arises discretely from intimately connected phases of the material [2]. In the composite material investigated in this work the magneto-electric effect is expected to be mediated by lattice strain. In such a material one phase should be piezoelectric and the other magnetostrictive. On applying an external elec- tric or magnetic field, strain is induced in to the piezoelectric or magnetostrictive phase respectively and gets transferred through the interface. This stress causes a change in magneti- zation or polarization on the other phase. The interfacial area and interfacial couplings can be greatly enhanced by reducing the particle sizes to nanometer dimensions, which may * Jacob Philip jphilip6012@gmail.com 1 Department of Instrumentation, Cochin University of Science and Technology, Cochin 682 022, India 2 Amal Jyothi College of Engineering, Kanjirapally, Kottayam 686518, India J Electroceram DOI 10.1007/s10832-015-0003-0