Minimizing of power loss in Li–Cd ferrite by nickel substitution for power applications R.K. Kotnala b,n , M. Abdullah Dar a,b , Vivek Verma b , A.P. Singh b , W.A. Siddiqui a a Department of Applied Science, Jamia Millia Islamia University, New Delhi 110025, India b National Physical Laboratory (CSIR), Dr. K.S. Krishnan Road, New Delhi 110012, India article info Article history: Received 15 April 2010 Available online 27 July 2010 Keywords: Ferrite Dielectric Impedance Magnetic Power loss abstract The effect of Ni substitution on the microstructure, dielectric, impedance, magnetic and power loss properties has been investigated on a series of Li 0.35–0.5x Cd 0.3 Ni x Fe 2.35–0.5x O 4 (0.00 rx r0.08) ferrite prepared by citrate precursor method. Dielectric and impedance measurements have been determined in the frequency range 100 Hz–10 MHz. An enhancement in permittivity was observed with Ni concentration and exhibits the maximum value of 7  10 3 for x ¼0.02 sample. The impedance spectroscopy technique has been used to study the effect of grain and grain boundary on the electrical properties of all the samples. Power loss measurements have been carried out in the frequency range 50 kHz–5 MHz at induction condition of B ¼10 mT. Power loss has been found to be quite low, less than 100 kW/m 3 up to 500 kHz, with the substitution of Ni in Li 0.35–0.5x Cd 0.3 Ni x Fe 2.35–0.5x O 4 ferrite, which is useful for technological aspects. & 2010 Published by Elsevier B.V. 1. Introduction Magnetic particles have received considerable attention in the past few years due to their scientific and technological impor- tance. Pure and substituted lithium ferrites form an important class of magnetic material due to their high saturation magneti- zation, resistivity and Curie temperature. Magnetic and electrical properties of ferrites have been found to be sensitive to their composition and processing techniques [1–3]. Among the chemi- cal synthesis methods, citrate precursor method appears to be simple and convenient, which gives more uniformity of particles and magnetic properties are immensely improved [4,5]. Ferrites have many technological applications in the field of electronics and telecommunication industry such as in microwave devices, memory core applications, power transformers, etc. owing to their high saturation magnetization, Curie temperature and low power loss [6–9]. The role of substituent in modifying the properties of basic ferrites has been widely studied. Development of high quality, low cost and low loss for high frequency ferrite material for power applications is an ever challenging aspect for research- ers. Substituted lithium ferrites may be useful material for such applications because of their modified magnetic and electrical properties [10–12]. The main types of losses encountered in ferrites are the hysteresis loss (p h ), eddy current loss (p e ) and residual loss (p r ). Hysteresis loss (p h ) can be minimized if one reduces the hindrances to domain wall movements by reducing their concentration and their individual influence. This requires a low volume fraction of pores, impurities and dislocations, but also a low level of stresses, a small magneto-crystalline anisotropy, a small magneto-striction and a high saturation magnetization. The magneto-crystalline anisotropy, magneto-striction and sa- turation magnetization can be controlled by the chemical composition [13] according to the applications. The eddy current loss (p e ) becomes progressively more important at higher frequencies. It can be reduced by providing a high electrical resistivity, that is, to increase the resistivity of polycrystalline ferrites by increase in grain boundary resistivity either by careful control of the processing conditions or by adding glass-forming dopants, and to increase the resistivity inside the grains [14,15]. Residual loss (P r ) plays an important role in reducing power loss in the high frequency range. To reduce residual loss (P r ), the complex permeability has to be made to peak at the frequency as high as possible, and this can be achieved using fine-grained ferrites [16]. Small grains can be realized using finer powders, enabling sintering at lower temperatures during shorter periods. Also applying sinter acids, such as Bi 2 O 3 , may lower the sintering temperature and thus yield small grains [13,15]. Because of their low melting point, these oxides melt at grain boundaries and initially act as a grain growth inhibitor, but special attention should be paid to homogeneous distribution of the additives, otherwise secondary grain growth may deteriorate the ferrite. In applications like memory core devices, where high saturation magnetization is essential, Cd substitution is desirable as it Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/jmmm Journal of Magnetism and Magnetic Materials 0304-8853/$ - see front matter & 2010 Published by Elsevier B.V. doi:10.1016/j.jmmm.2010.07.033 n Corresponding author. Tel.: +91 11 45608599. E-mail address: rkkotnala@mail.nplindia.ernet.in (R.K. Kotnala). Journal of Magnetism and Magnetic Materials 322 (2010) 3714–3719