INTRODUCTION:
Ni-Zn ferrites are materials have versatile applications including biomedical, industrial, and high frequency fields, because of their reduced magnetic losses [1]. In the spinel ferrite, Zn2+ ions mostly occupying tetrahedral sites (A) while Ni2+ prefer in octahedral site (B) [2]. The system of spinel structure ZnNiFe2O4 with a formula, [Fe1-xZn2+x]A [Ni1-xFe1+x]BO4. Magnetic properties of Ni-Zn are due to the presence of magnetic (Fe3+) ions situated at A and B sites and their interaction with surrounding oxygen ions. These oxygen ions affect the electronic configuration of the enclosed Fe3+ ions and provide the super exchange interaction between the Fe ions in different sites [3].
There are various methods to prepare nanoferrites such as co-precipitation, citrate gel method, precursor method and hydrothermal methods. Among these, sol–gel auto combustion is suitable, effective and low cost method [4] for production of ferrite nanoparticles. This process involves a self-sustained reaction in homogeneous solution of different oxidizers (metal nitrates) and fuel (urea). Due to extraordinary properties of Ni-Zn ferrite, it has found potential applications in the fields, such as magnetic feeder for transmitter, Hyperthermia, microwave communication system pulsed current monitor and gas sensors [5]. The present research work deals with synthesis of Zr4+ substituted Ni-Zn ferrite, various concentrations of Zr4+ are doped at the crystal structure of Ni-Zn ferrite to know the behavior of structural, electrical and magnetic effect of Zr4+ content [6]. Zirconium substituted Ni-Zn ferrite with composition ZrxZn0.5-xNi0.5-xFe2O4 (x = 0.10, 0.20, 0.30) were synthesized by solution combustion method.
EXPERIMENTAL:
MATERIALS:
ZrxZn0.5-xNi0.5-xFe2O4 (x = 0.10, 0.20, 0.30) nanoparticles were synthesized by sol-gel auto combustion method using urea as a fuel. Stoichiometric proportions of metal nitrate separately dissolved in 10 ml double distilled water and adding 1 mole urea in it, where x= 0.1, 0.2 and 0.3. The resulting solutions were mixed and stirred at room temperature. The mixed solution was then heated at 60°C till one-fourth solution is left, up to the mark of formation of viscous gel, then the gel were kept in microwave oven for instant fire at 600 watt. The dried gel started and finally powder was obtained. Prepared ferrite powder was grinded for 4 hrs and annealed at 800 0C for 4 hrs in muffle furnace. At last the powdered material is grinded in agate mortar for another four hour to obtain final product.
Characterization of materials:
The phase identification of materials were obtained by using X-Ray Diffraction (XRD) using Cu Kα- radiation in the range of 10 -80° of the 2θ. The morphologies of the powder samples were analyzed by transmission electron microscopy (TEM). The magnetic measurements were made by using vibrating sample magnetometer (VSM) at room temperature. DC electrical measurement was carried out using two probe method and digital multimeter.
RESULTS AND DISCUSSION:
X-ray diffraction analysis:
Figure 1 shows the X-Ray Diffraction (XRD) patterns of ZrxZn0.5-xNi0.5-xFe2O4 (0.1≤x≤0.30), of Ni-Zn ferrite. The cubic spinel structure of nickel ferrite is confirmed from the (hkl) planes (200), (311), (222), (400), (422), (333) and (440). Crystallite size D was calculated using the Debye–Scherrer equation [7].
Where ‘λ’ is the wavelength of Cu Kα- radiation, ‘β’ is the full width half maximum of diffraction peak, and ‘θ’ is the Bragg angle. The XRD measurements were carried out using Cu Kα radiation (λ = 1.54 Å). The unit cell volume is 596.3098 Å3 and average crystallite size D is 47 nm. All the peaks are impeccably match with the cubic crystalline phase of Ni-Zn ferrite (JCPDS Card No. 008-0234) [8]. The diffraction peaks move towards the minimum angle with a small increase in Zr ions concentration. The miller indices and intensities of ZrxZn0.5-xNi0.5-xFe2O4 nanoparticles as a function of Zr substitution (x) are shown in figure 1. It has been seen that all samples have single phase of cubic spinel structure. The lattice parameter (a) was find out using the relation [9]
Where ‘h’, ‘k’ and ‘l’ are miller indices of plane. The lattice parameter (a) of ZrxZn0.5-xNi0.5-xFe2O4 nanoparticles as a function of Zr substitution (x) is shown in figure 2. We know that the ionic radius of Zr4+= 0.79 Å, Zn2+= 0.74 Å, Ni2+= 0.72 Å and Fe3+= 0.64 Å which indicates that the lattice parameter grow with further increase in zirconium substitution concentration. The attraction force of oxygen ions for tetravalent zirconium is more than those for trivalent (Fe3+) and divalent (Ni2+ and Zn2+) ions. Thus bond length and lattice parameter do not increase drastically. Therefore, the comparison between ionic radii and attraction forces is responsible for linear graph of lattice parameter [10].
Fig.1: XRD pattern of ZrxZn0.5-xNi0.5-xFe2O4
Fig.2: Lattice parameter variation of ZrxZn0.5-xNi0.5-xFe2O4
Structure analysis:
Figure 3 shows the morphologies of ZrxZn0.5-xNi0.5-xFe2O4 nanoparticles with the help of transmission electron microscope (TEM). It exhibit the grain size of particles is symmetrical with Zr substitution and the average grain size is about 58 nm, 52nm and 43 nm with x = 0.10, 0.20, and 0.30 respectively [11], which signify that the average grain size decreases with the increase of Zr concentration in sample [12]. The outcome of TEM analysis can be describedin terms of the increased pore mobility due to the formation of large amount of cation vacancies, therefore higher valence cations creates excess of cation vacancy in the cubic system. In the present case Zr4+ substitution reduces the grain growth of Ni-Zn ferrite nanoparticles as reaction center by the increase of the bulk diffusion due to the aberration and activation of crystal lattice, which is caused by Zr substituted [13].
Fig.3: TEM images of ZrxZn0.5-xNi0.5-xFe2O4
Magnetic Properties studies:
The vibrating sample magnetometer (VSM) was used for analyzing the Magnetic properties of the samples with the applied magnetic fields between +15000 Gauss to - 15000 Gauss measured at room temperature. Figure 4.shows the variation of magnetization B (emu/g) versus the applied magnetic field H (Gauss) of ZrxZn0.5-xNi0.5-xFe2O4 nanoparticles. It is noted that hysteresis loops of Zr doped Ni-Zn nanoparticles seems to be typical ferrimagnetic nature [14]. The coercivity (Hc), saturation magnetization (Ms) of Zr substitution nanoferrites are shown in figure5. The saturation magnetization (Ms) decreases step by step with the increase of zirconium substitution and reaches its lowest value at x= 0.30 and coercivity (Hc) reaches minimum at 0.10 [15]. Saturation magnetization (Ms) reaches the minimum (18.24 emu/g) at x=0.30 and Retentivity (Mr) reaches the minimum (0.11 emu/g) with Zr substitution (x= 0.20). In addition of Zirconium ions the saturation magnetization decreases, because the average magnetic domain size of the particle is changing and the atomic spins are getting more and more aligned in the direction of the applied magnetic field [16].
Fig.4: VSM of Zr doped ZrxZn0.5-xNi0.5-xFe2O4
Squareness ratio of ZrxZn0.5-xNi0.5-xFe2O4
The saturation magnetization (Ms), coercivity (Hc), retentivity (Mr) and squareness ratio (Mr/Ms) are given in table1.
Table 1 shows that initially Hc decreases first up to x=0.20 then suddenly rise for x = 0.30. The retentivity is directly proportional to porosity [17], thus with the increase in Zr concentration from x = 0.10 to x = 0.20, the porosity decreases and thus retentivity also decreases whereas when the porosity starts increasing after x =0.20 and the retentivity also starts increasing. The porosity were calculated from TEM images using ‘Image –J software’ shown in table 1. The low retentivity and low coercivity of soft magnets used for hyperthermia and transformer core [18].
DC electrical studies
DC electrical resistivity is one of the important characterization techniques to understand its conductivity mechanism. The electrical resistivity with different concentration for Zr4+ doped nanoparticles is shown in figure 5. The variation in resistivity with increase in concentration has been noted therefore the present sample is highly resistive in nature [19]. Figure 5 shows variation of resistivity at room temperature with the increase in doping concentration of zirconium ions. Resistivity decreases from a value of 850.68 MΩcm for the doping content x = 0.10 and reaches 100.26 MΩcm for x = 0.20, but moderately increases with further increase in the doping concentration and obtain 150.76 MΩcm for x = 0.30. This is due to the hopping of electrons between Fe ions with variable of divalent and trivalent valence at the octahedral sites. The conductivity of solid crystal depends on electrons density, height and width of the tunneling barrier [20]. It is observed that the resistivity of ZrxZn0.5-xNi0.5-xFe2O4 samples falls between 850.68 MΩcm to 100.26 MΩcm. Thus the material has large electron density and low tunneling barrier all the above phenomenon happened due to the substitutions and distribution of Zr and Fe ions in the lattice site. Because of larger valance the zirconium and iron are surrounded by oxygen anions which can spilled the energy level of electron orbital of respective atoms, larger energy gap exponentially increase the solid crystal in a poor conductor perhaps an insulator or a semiconductor. The electrical resistivity (ρ) has been calculated by using the below formula
Where ‘R’ is the resistance, ‘A’ is the area of pellet and ‘l’ is the thickness of pellet.
Fig.5: Resistivity versus concentration for ZrxZn0.5-xNi0.5-xFe2O4
Table 2: Electrical resistivity of Zr substituted Ni-Zn ferrite nanoparticles
|
Concentration (x) |
Resistance (R) MΩ |
Area of pellet (A) cm2 |
Thickness of pellet (l) cm |
Resistivity (ρ) MΩcm |
|
0.10 |
1083.67 |
0.157 |
0.2 |
850.68 |
|
0.20 |
127.39 |
0.157 |
0.2 |
100.26 |
|
0.30 |
192.06 |
0.157 |
0.2 |
150.76 |
CONCLUSION:
Zirconium substituted Ni-Zn ferrite nanoparticles have been successfully synthesized by sol-gel auto combustion method. XRD analysis indicates the diffraction peaks move towards the lower angle and the lattice parameter increases with substitution zirconium. TEM analysis shows the concentration Zr4+ ions is inversely proportional to average grain size of Ni-Zn ferrite nanoparticles. The magnetic properties of synthesized Zr doped nano materials have an exclusive superparamagnetic property which can be used for hyperthermia. The electrical resistivity study shows that the resistivity value range between 100.26 MΩcm to 850.68 MΩcm, thus the material is well suited for applications of high frequency and power supply transformers due to low power loss caused by hysteresis and eddy currents.
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Received on 18.11.2017 Modified on 22.01.2018 Accepted on 29.01.2018 ©A&V Publications All right reserved Research J. Science and Tech. 2018; 10(1): 13-18 DOI:0.5958/2349-2988.2018.00003.7 |
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