Effect of Zn Concentration on NiZnFe2O4 Nanoparticles

Effect of Zn Concentration on NiZnFe2O4 NanoparticlesCHAPTER-7EFFECT OF Zn CONCENTRATION ON MAGNETIC AND DIELECTRIC PROPERTIES OF NiZnFe2O4 NANOPARTICLES7.1 INTRODUCTIONNi (1-x) Zn (x) Fe2O4 (x=0.2, 0.4 and 0.6) nanoparticles are synthe coatd by using coprecipitation method. Zinc is a known metal, its role is important in the modification of ferrite properties by redistribution over the tetrahedral and octahedral sites of the spinel lattice. Rath et al (2002) describe the event of coat substitution on lattice statement and magnetised properties on Mn-Zn ferrites prepared by hydrothermal precipitation method. Arulmurugan et al (2005) studied the effect of surface substitution on Co-Zn and Mn-Zn ferrite nanoparticles prepared by coprecipitaion method.This chapter discusses the effect of zinc assiduousness on structural, magnetic and dielectric properties of NiZnFe2O4 nanoparticles prepared by co-precipitation method. The detailed experimental routine involved in the preparation of NiZn ferrite nanoparticles has been already reported in chapter IV. In this method three different organizations such as x=0.2, x=0.4 and x=0.6 were used in the chemical formula Ni (1-x) Zn(x) Fe2O4 to analyze the properties of the ferrite nanoparticles.7.2 RESULTS AND DISCUSSION 7.2.1 X-ray Diffraction (XRD) analysisThe average cryst solelyite size t and the lattice parameter a were calculated from X-ray diffraction data as reported in the chapter IV. The care fors of particle size and wicket door parameter of completely samples are likewise tabulated in Tables 7.1, 7.2 and 7.3.The particle size decreased from 24 to 12nm with the ontogeny of Zn tightfistedness. The same behavior of decrease in particle size with the increase of zinc constriction was also observed for the samples work at 600C and 900C. The decrease in particle size due to the increase of zinc concentration was 26 to 20nm for shape sample at 600C and 31 to 25 nm for mould sample at 900C respectively.T his variation of particle size with zinc concentration at the above mentioned sintering temperature of Ni Zn ferrites nano particles is shown in Fig.7.1. The above observation shows that the presence of zinc blocks the grain growth.The clear temperature affects the molecular concentration at the surface of the crystal, and hence, the crystal growth (Upadhyay et at 2004). The formation of Zn-ferrite is more exothermic as compared with the formation of Ni-ferrite (Navrotsky Kleppa 1968). Thus, the crystal surface temperature increases with addition of zinc, decreasing the molecular concentration at the crystal surface and hence, obstructing the grain growth.The effects of zinc concentration on structural, magnetic and dielectric properties of Ni-Zn ferrite nano particles were studied. Particle size decreased with the increase of concentration. This decreasing in particle size behavior was observed for all the categories of concentration variation at different sintering temperature l evels. The effect of zinc concentration on particle size showed a reverse effect compared with the effect of sintering temperature (chapter-IV), in which the particle sizes increased with the increase of sintering temperature.Table 7.1Particle size and Lattice parameter of as prepared Ni (1-x) Zn (x) Fe2O4(x= 0.2, 0.4 and 0.6) nano particlesTable 7.2 Particle size and Lattice parameter of Ni (1-x) Zn (x) Fe2O4(x= 0.2, 0.4 and 0.6) nano particles mold at 600CTable 7.3 Particle size and Lattice parameter of Ni (1-x) Zn (x) Fe2O4(x= 0.2, 0.4 and 0.6) nano particles sintered at 900CFrom Tables 7.1, 7.2 and 7.3 it is also observed that the lattice parameter increases with the increase of zinc concentration. The lattice parameter take to be for as prepared are increased from 8.33 to 8.37 with the increase of zinc. For the samples sintered at 600C the lattice parameter value for lower zinc concentration (x=0.2) is 8.63 and high zinc concentration (x=0.6) is 8.66 . The similar behavior o f increase in lattice parameter with zinc concentration is also observed as 8.64 to 8.68 in the samples sintered at 900C. This increase of lattice parameter with zinc concentration for all sintering temperatures of Ni Zn ferrites nano particles are also shown in Fig.7.2. The addition of Zn2+ in Ni-ferrite causes the Fe3+ ions to emigrate from A site to B site. The larger ionic radius of zinc (0.82), compared with ferric ion (0.67 ), makes the A site and thus the lattice expands, increasing the lattice parameter. A similar variation of particle size and lattice parameter with zinc content had been observed by Joshi Kulkarrni (1986) for Mg-Zn Ferrite.Fig.7.1 renewing of particle size with zinc concentration for all sintering temperaturesFig.7.2Variation of lattice parameter with zinc concentration forall sintering temperature7.2.2 Magnetic PropertiesThe room temperature B-H hysteresis loops of Ni (1-x) Zn (x) Fe2 O4 nano particles for different zinc concentration (x = 0.2, 0.4 and 0.6) sintered at 600C and 900C are shown in Figs.7.3 (a), 7.3 (b) and 7.3 (c). The variations of magnetic properties such as fertilization magnetic intensity (Ms), and coercivity (Hc) for different zinc concentrations (x = 0.2, 0.4 and 0.6) at particular sintering temperature were calculated from the hysteresis data and tabulated in Tables 7.4, 7.5 and 7.6.Table 7.4 Saturation magnetisation and coercivity values of as preparedNi (1-x) Zn (x) Fe2O4 (x= 0.2, 0.4 and 0.6) nano particlesTable 7.5 Saturation magnetization and coercivity values of Ni (1-x) Zn (x) Fe2O4(x= 0.2, 0.4 and 0.6) nano particles sintered at 600CTable 7.6 Saturation magnetization and coercivity values of Ni (1-x) Zn (x) Fe2O4(x= 0.2, 0.4 and 0.6) nano particles sintered at 900CThe effect of zinc concentration on magnetic properties such as impregnation magnetization and coercivity of all compositions of Ni Zn ferrite nano particles sintered at 600C and 900C are shown in Figs.7.4 and 7.5. The Fig.7.4 reveals tha t the intensity magnetization (Ms) decreases with the increase of zinc concentration. The saturation magnetization value decreased from 29.73 to 6.98 emu/g with the increase of zinc concentration for as prepared samples. The saturation magnetization value for the 600C sintered samples at lower zinc concentration (x=0.2) was 32.78 emu/g and high zinc concentration (x=0.6) was 25.80 emu/g. A similar behavior of decrease in saturation magnetization with zinc concentration was also observed in the samples sintered at 900C as 64.34 to 39.50 emu/g.Fig.7.3 Hysteresis loops of Ni (1-x) Zn (x) Fe2 O4 nano particles for different zinc concentration (x = 0.2, 0.4 and 0.6)(a) as prepared (b) 600C sintered (c) 900C sintered samplesThis decreasing of saturation magnetization with the increase of non magnetic Zn concentration is due to the interaction created by the zinc in the tetrahedral and octahedral sites. This shows the weakening of A-B interaction, whereas B-B interaction changes from fer romagnetic to antiferromagnetic state. The occurrence of pip-squeak decrease in saturation magnetization is also evidenced from the dielectric study, because it shows that there is a minor increase in dielectric unvarying. This reason leads to the closedown that saturation magnetization variation with respect to concentration for 600C and 900C samples did not cause a rapid decrease in saturation magnetization like as prepared sample.Fig.7.5 shows that the coercivity values of NiZn ferrite nanoparticles decrease with the increase of zinc concentration. The coercivity values of as prepared nanoparticles decrease from 324.36 to 306.56 Gauss. Similarly the variation of coercivity values of nanocrystalline NiZn ferrite particles with increase of Zn concentration sintered at 600C and 900C are in the range of 347.31- 340.72 Gauss and 386.67-351.34 Gauss. This is due to the decreases of magneto crystalline anisotropy constant quantity. The magneto crystalline anisotropy constant is negat ive for both Ni and Zn ferrites. The absolute value of magneto crystalline anisotropy constant larger for Ni ferrites than that of Zn ferrites (Verma et al 2000). The total anisotropy is personify to the sum of their individual anisotropy. So magneto crystalline anisotropy constant and hence coercivity decreases with the increase in Zn concentration. Also reasons behind the decrease in saturation magnetization and decrease in coercivity are clearly identified from the formation of smaller particle size even at the higher Zn concentration at all sintering temperatures.Fig.7.4 Variation of saturation magnetization with zinc concentrationFig.7.5 Variation of coercivity with zinc concentration7.2.3 insulator propertiesThe effect of zinc concentration on dielectric constant of all samples of Ni (1-x) Zn (x) Fe2 O4 nano particles are shown in Figs.7.6 (a), 7.6 (b) and 7.6 (c). The values of dielectric constant and dielectric loss are tabulated in Tables 7.7, 7.8 and 7.9.Fig.7.6 insulator constant curves of Ni (1-x) Zn (x) Fe2 O4 nano particles fordifferent zinc concentration (x = 0.2, 0.4 and 0.6)(a) as prepared (b) 600C sintered (c) 900C sintered samplesFig. 7.7 Dielectric loss curves of Ni (1-x) Zn (x) Fe2 O4 nano particles for different zinc concentration (x = 0.2, 0.4 and 0.6)(a) as prepared (b) 600C sintered (c) 900C sintered samplesThe dielectric constant attained for zinc concentration x =0.6 led to a higher value for all the samples. The variations of dielectric constant with zinc concentration for all samples are also shown in Fig. 7.8. For all as prepared samples, the dielectric constant value increased from 10.92 to 25.08 with the increase of zinc concentration. The dielectric constant value for the samples sintered at 600C in lower zinc concentration (x=0.2) was 15.33 and it increased to 32.86 at higher zinc concentration (x=0.6). A similar behavior of increase in dielectric constant with increase in zinc concentration was also observed in the samples s intered at 900C as 19.37 to 48.18.Table 7.7 Dielectric constant and Dielectric loss values as preparedNi (1-x) Zn (x) Fe2O4 (x= 0.2, 0.4 and 0.6) nano particlesTable 7.8 Dielectric constant and Dielectric loss values ofNi (1-x) Zn (x) Fe2O4 (x= 0.2, 0.4 and 0.6) nano particlessintered at 600CTable 7.9 Dielectric constant and Dielectric loss values ofNi (1-x) Zn (x) Fe2O4 (x= 0.2, 0.4 and 0.6) nano particlessintered at 900CFigs.7.7 (a), 7.7 (b) and 7.3 (c) show the effect on zinc concentration on dielectric loss factor of all samples of Ni (1-x) Zn (x) Fe2 O4 nano particles. The variation of dielectric loss factor value with zinc concentration for all sintering temperatures is also shown in Fig. 7.9. For all as prepared samples the dielectric loss factor value increased from 0.59 to 1.36 with the increase of zinc concentration. For the samples sintered at 600C the dielectric loss factor value for lower zinc concentration (x=0.2) was 0.68 and at higher zinc concentration (x=0.6) it was 1.61. A similar behavior of increase in dielectric loss with increase in zinc concentration was also observed in the samples sintered at 900C as 1.34 to 2.14.In Ni-Zn ferrites Zn occupies A site and Ni occupies Bsite, while Fe occupies both A and B sites. When Zn2+ is added in the place of Ni2+, with increase in Zn composition x, some of the Fe3+ ions get converted into Fe2+ ions. This increases the hopping between Fe3+ and Fe2+ ions, thereby decreasing the resistance of the grain. This increases the probability of electrons reaching the grain boundary. Hence the polarization and the dielectric constant increase.Fig.7.8 Variation of dielectric constant with zinc concentrationFig.7.9 Variation of dielectric loss with zinc concentration7.3 CONCLUSIONThe effects of zinc concentration on structural, magnetic and dielectric properties of Ni-Zn ferrite nano particles were studied. The increase in zinc concentration obstructed the grain growth and decreased the particles size. The larg er ionic radius of Zn, increased the lattice parameter values of NiZn ferrite nanoparticles with the increase of its concentration. The non magnetic property of zinc, decreased the saturation magnetization and coercivity values of NiZn ferrite nanoparticles. The dielectric constant and dielectric loss factor values also increased with the increase of zinc concentration due to the increase of probability of electrons reaching the grain boundary. Low value of particle size obtained at higher zinc concentration in the present work indicated that NiZn ferrite nano particles in lower nanometer scale could be obtained at higher zinc concentration.