Effect of Calcination Temperature on Physical properties of Ni0.6Zn0.4Fe2O4 Ferrite nanoparticles

The inuence of Calcination temperature on the physical properties of Ni 0.6 Zn 0.4 Fe 2 O 4 ferrite nanoparticles were investigated. These ferrite nanoparticles have been synthesized by sol-gel auto combustion method using citric acid as fuel agent at different calcination temperatures (400 0 C, 500 0 C and 600 0 C). The Morphological investigation, average crystallite size and microstructure of the material were examined by using X-ray diffraction (XRD) and conrmed by eld emission scanning electron microscope (FESEM) and FTIR spectra. The Effects of calcination temperature on the dielectric and magnetic properties were calculated by using LCR meter and vibrating sample magnetometer (VSM). The XRD result shows a single-phase cubic spinel structure with average crystallite size increases from 27 to 29.5 nm, with an increase of temperature. The highest saturation magnetization was found at a calcination temperature 600 0 C with value 80.39 emu/g, and the value coercive eld (H c ) was inverse with the crystallite size.


Introduction
The spinel ferrites have concerned much attention in recent years due to their exceptional magnetic, electrical properties and chemical stabilities [1][2][3]. Nanoscale NiFe 2 O 4 is one of the versatile and technologically important soft ferrite materials with signi cant qualities such as low coercivity, high electrical resistivity and chemical stabilities, catalytic behaviour, etc. Because of these properties, NiFe 2 O 4 nanoparticles have various potential applications in magnetic uids, electrodes, catalysis, sorbent, gas sensor, and biomedicine [4][5][6][7][8]. In general, the spinel ferrites attained a chemical formula is AB 2 O 4 , where 'A' and 'B' can indicate the tetrahedral and octahedral sites, respectively. In other words, the divalent cations such as Ni + 2 , Mg + 2 , Zn + 2 , Co + 2 , Cu + 2 and Mn + 2 can occupy the A-site while the B site can be occupied by trivalent cation like Fe + 3 [9,10]. For example, NiFe 2 O 4 and ZnFe 2 O 4 can exhibit a cubic spinel structure [11,12]. Nevertheless, these spinel structures will be again classi ed into three types (normal spinel, inverse spinel and mixed spinel) based on the degree of inversion (0 < δ < 1). The δ = 1, δ = 0 and δ = 0.25 for normal spinel, inverse spinel and mixed spinels, respectively [13]. Normally, the degree of inversion was inter-linked to the cation distribution between A and B-sites. This cation distribution was observed to be different for bulk and nano ferrites. Both Ni and Zn ferrites are known to have a dominant preference for tetrahedral and octahedral locations, whereas nickel ferrite is an inverse spinel ferrite and zinc ferrite is a normal spinel ferrite. The composite Ni -Zn ferrites, however, are known to exist as a completely mixed spinel structure. The variation of elemental composition in these ferrites results in the redistribution of metal ions over the tetrahedral and octahedral sites, which can alter the properties of ferrites. The properties of these ferrite nanoparticles can also be tailored by altering parameters such as doping concentration or the synthesis process [14]. Because of this NiZn ferrites are prepared and studied for distinct physical properties.

Experimmental
The chemical formula of considered Mg-doped Zn ferrite is Ni 0.6 Zn 0.4 Fe 2 O 4 was prepared using the solgel auto combustion method.  3 ) is for maintaining the pH level of solution. The nitrates were dissolved using distilled water separately in a glass beaker. They were mixed into a large beaker using magnetic stirrer after the individual chemicals had been fully dissolved. After some time a clear solution was formed, maintain citric acid to nitrate ratio as 1:3 by adding two solutions. From the previous works of literature, we consider 1:3 molar ratio is suitable for obtaining less agglomeration and tiny sized particles.
Maintaining pH value equal to 7 by adding ammonia (NH 3 ) drop by drop under constant stirring. The previous works of literature also indicate that the size of the particles depends on the pH value. After a few hours, during the stirring and heating stage observed the homogenous solution. By continuous heating and stirring at 150°C, water molecules evaporated continuously after some time a dense and extremely sticky gel was found.
This gel was heated in the temperature range180 0 C-220 0 C. After some time, evapourate the water molecules completely, at the time of instant observe the burning of gel automatically give rise to auto combustion, it is very quick due to the evolution of gaseous products. Moreover, after a while, the full gel transformed to ashes or smouldered, "erupting like a volcano from the lower of the beaker to the upper. This process was completed in no moment. The obtained powders colures in dark brown ash were produced at temperature 250 0 C in the form of a tree structure. Finally, the powder was cooled to room temperature. The complete preparation steps are shown in Fig. 1 The agate mortar is used to grind the powder for 30 minutes, then samples are obtained in the form of incredible dense.
Finally obtained powder specimen is calcinated under standard circumstances at temperature 400 0 C, 500 0 C and 600 0 C about 4 hours and maintain room temperature. Also, all prepared powder samples are tested for structural analyses, using various techniques XRD, SEM and EDS. VSM is used for magnetic study and LCR meter for dielectric study. of 20 0 to 80 0 angle. The peak intensity equivalent to a structure is displayed in terms of % of miller indices as shown in Fig. (2). The obtained X-ray diffraction pattern suitable with JCPDS card no.10-325. There was a change in the Zn ferrite structure with the addition of Ni content [15].
The pattern of Ni 0.6 Zn 0.4 Fe 2 O 4 can be indexed as a pure cubic spinel structure and found to the presence of secondary phases. The doping of Ni content, extra peaks arises corresponding to the nickel composition as indicating with the "♦" symbol shown in gure(2) [15]. The most intense (311) peak of cubic spinel ferrite observed as a measure of its degree of good crystallinity. The crystallite size (D) of Ni 0.6 Zn 0.4 Fe 2 O 4 sample was calculated by using the Scherrer formula is given by Where k = 0.9 is Scherrer's constant, λ = 1.5406 Å is the wavelength of the incident x-rays, β is the full width at half maximum (FWHM) of diffraction peak, and θ is the Bragg's angle of diffraction. The SEM analysis is used to study the morphology of all the samples. Figure (4) shows SEM micrographs of Ni 0.6 Zn 0.4 Fe 2 O 4 specimen. All micrographs showed the same magni cations. From the SEM images, it can be found that synthesized samples contain nanoparticles. Hence, the prepared nanoparticles look like spherical, dispersed and less agglomeration. From SEM study, the observations on grain size reveal that increasing nature with an increase of calcination temperature and changed like the XRD analysis.     Table 3. IR results indicate two prominent bands around 600 and 400 cm − 1 in all samples due to vibrations of tetrahedral and octahedral sites [18]. Hence, con rm the prepared samples having a single phase with a homogenous structure.  The observed frequency bands (ν 1 ) in the range of 557 to 577 cm − 1 are considered as the high-frequency bands (strong absorption), whereas the frequency bands (ν 2 ) in the range of 418 to 420 cm − 1 are considered to be the low-frequency bands (weak absorption). The increase in calcination temperature causes an increase in the high-frequency bands and lower frequency bands [19]. The dielectric constant (K) described based on the Maxwell-Wagner type of interfacial polarization that has an adequate agreement with Koop's theory [20]. Ferrites comprise of conducting grain with weak grain boundaries. Initially, the electrons follow the applied eld and piled up at the grain boundaries through the exchange mechanism that forms polarization. However, at a speci c frequency, the hopping of electrons between Fe 2+ /Fe 3+ ions can not follow the eld, and it consumes a de nite time to align in the eld direction that triggers to reduce the polarization. Hence the dielectric constant decreases.   Declarations