1. 2. Sample Structure Effect of sintering temperature on dielectric loss, conductivity relaxation process and activation energy in Ni 0.6 Zn 0.4 Fe 2 O 4 ferrite M. A. Ali 1, M. N. I. Khan 2, F. -U. -Z. Chowdhury 1, S. Akhter 2, B. Anjuman 2, A. Parveen 2 and M. M. Uddin 1 1 Department of Physics, Chittagong University of Engineering and Technology (CUET), 2 Materials Science Division, Atomic Energy Center, Dhaka. National Conference on Physics Research and Education in Bangladesh. 24-25 April, 2015, AEC, Dhaka, Bangladesh. Polycrystalline ferrite with basic chemical composition Ni 0.6 Zn 0.4 Fe 2 O 4 has been prepared by solid state reaction at different sintering temperatures (T s ) 1200 °C, 1250 °C and 1300 °C. Transport properties of the sample have been measured at room temperature. DC-resistivity decreases with increasing T s which confirms the semiconducting behavior of the prepared ferrites. Activation energy decreases with increasing T s. Dielectric properties such as dielectric constant (ε´), dielectric loss factor (ε´´) and dielectric loss tangent (tanδ) have also been measured. The relaxation frequency(f R ) has been obtained from frequency dependent imaginary part of electric modulus (M´´) at different T s. The value of relaxation times (  ) are found to be 53, 8, and 8 ns for T s = 1200 °C, 1250 °C and 1300 °C, respectively. Keywords: DC-resistivity, activation energy, dielectric constants, electric modulus. Ni-Zn ferrite. Abstract Ni–Zn ferrites have been received a great deal of interest for many years due to its low magnetic coercivity, high resistivity values, low eddy current loss in high frequency operations (10–500 MHz) [1-2]. Although the effect of sintering temperature, T s, on the structural, dielectric, resistivity and magnetic properties of (Ni,Zn)Fe 2 O 4 ferrite have been investigated [3-5]. To the best of our knowledge, the effect of T s on the non-Debye type dielectric relaxation, electron spin life time, and electric modulus in conventional double sintering derived Ni 0.6 Zn 0.4 Fe 2 O 4 ceramics have not been reported yet. In this report, we have investigated structural and transport properties of Ni 0.6 Zn 0.4 Fe 2 O 4 ceramics over a wide frequency range, prepared by the conventional double sintering method. 1. Introduction 2. Materials and Methods Frequency dependence of the dielectric permittivity (  ) 3. Results and Discussion Fig. 3. Variation of (a) dielectric constants and (b) dielectric loss tangent with frequency. The real part (M) and imaginary part (M) of electric modulus as a function of frequency at different T s has been depicted in Fig.4 (a). The value of M reaches a maximum at high frequency region with reaching to zero at low frequency indicates that the electrode polarization contribution is negligible. The frequency dependence M’’(ω) is characterized by a clearly resolved peak which shifts towards higher with sintering temperature. The characteristic frequency at which M’’(ω) is maximum (M’’ max ) corresponds to relaxation frequency and is used for the evaluation of relaxation time. The obtained value of relaxation time at different T s is shown in Fig. 4 (b). Fig. 4. Variation of (a) electric modulus with frequency and (b) relaxation time with Ts. (b) (a) 4. Summary Single phase spinel structure of the Ni 0.6 Zn 0.4 Fe 2 O 4 ferrites at different T s is obtained. A decrease in resistivity as well as activation energy with T s has been observed. An increase in dielectric constant may be attributed to the conversion of trivalent Fe 3+ ions to the divalent Fe 2+ state via electron hopping. The collective contribution of both types of carriers to the dielectric polarization yields a clear peak (tanδ) with the frequency. The value of spin relaxation time (  ) is found to be several nanosecond, such a long relaxation time in NZFO ceramics can be very useful in nanoscale spintronic devices. Ts (°C) DC-resistivity (Ω-cm × 10 5 ) Activation energy (eV) Dielectric consts. (at 1 KHz) 12003.32 0.511.34×10 5 12500.58 0.257.76×10 5 13000.18 0.191.67×10 6 Table 1. Variation of DC-resistivity, activation energy, Dielectric constants with Ts References: 1.Anil Kumar et al. Mater. Lett. 27 (1996) 293–296. 2.Tsay et al. J. Magn. Magn. Mater. 209 (2000) 189– 192. 3.Costa et al. J. Magn. Magn. Mater. 256 (2003) 174–182. 4.Kothawale et al., Solid State Physics (India) Vol. 57 (2012). 5.Akther Hossaina et al., J. Magn. Magn. Mater. 312 (2007) 210–219. (b) The general preparation procedure of ferrite comprises of the following operations as shown in the flow chart below: Weighing by different mole percentage Dry mixing by Milling Pre-sintering MillingPressing to desired shape SinteringFinish Product Oxide of raw materials (Fe 2 O 3, NiO, ZnO) Fig. 1. (a)XRD pattern and (b) SEM images at different T s. Fig. 1 (a) shows the powder XRD patterns which reveal single phase spinel structure of Ni 0.6 Zn 0.4 Fe 2 O 4. It is also observed that the diffraction peaks become narrower and sharper with the augment of T s, indicating an increase of the crystallite size, which has been confirmed by SEM images as shown in Fig. 1(b). (a) (b) T s =1200°C T s =1250°C T s =1300°C Fig. 2. logρ vs 1/T graph at different T s. (a) Fig. 3. (a) depicts that the values dielectric constant decreases with the increase of frequency. A remarkable increase in the value of  has been observed for the higher T s sample. Frequency dependent tan  at different T s for NZFO is shown in Fig. 3 (b). The curve shows the dielectric relaxation processes (peaks) at the particular frequency that are shifted at the higher frequency value. The activation energy of electrical resistivity of the sample was calculated in eV unit from the slope of the plot 1 (b) as follows: E g = slope ×4.606×8.62×10-5