Spinel ferrites have been investigated for decades due to their interesting structural and magnetic properties . These materials can be synthesized at relatively lower temperatures, just by variation of the trivalent and divalent ions into the spinel lattice, therefore high speed devices can be fabricated from these materials for microwave and magnetic recording applications . Magnetite is known for its role in spintronics and is extensively used in traditional recording media . In the unit cell of spinel structure, there are 32-octahedral sites and 64-tetrahedral sites. Due to 16-octahedral and 8-tetrahedral sites, electrical neutrality is established by trivalent and divalent ions . From the discretion of structures, the ferrites are super-lattices . They have octahedral B-sites and tetrahedral A-sites in AB2O4 crystal structures . Depending on cations A and B sites, they can exhibit paramagnetic, antiferromagnetic, and ferromagnetic behavior . It is also investigated that structural and magnetic properties of the spinel ferrites are strongly affected by the presence of these metal ions in the spinel ferrite lattice, which prefer to settle down at the octahedral B-site in spinel as well as at tetrahedral A-site in spinel ferrite . The paramagnetic, ferromagnetic and antiferromagnetic characteristics of the compounds are attributed to the presence of these metal ions, which significantly influence the magnetic properties of the spinel ferrites .
Metal-oxide nanoparticles, which differ from their bulk counter parts, recently attracted the scientific community on account of their wide array of applications in optoelectronic industry. These significant properties also make the Metal oxide nanoparticles promising candidates for a large number of applications in recording technology as well as in biomedical . Moreover, synthesis of these spinel ferrites is a key parameter to achieve the required electrical and magnetic properties. It is well known fact that the synthesis of ferrites at lower temperatures has many potential advantages such as energy efficiency, low processing cost, and high production rate . There is a range of synthesis methods for production of spinel ferrites, including micro-emulsion, chemical co-precipitation, hydrothermal, ceramic method, sol-gel, etc. [11, 12]. However, over the last few years, the co-precipitation method has been intensively used to synthesize a variety of mixed-metal oxides, nano-scale materials, organic–inorganic hybrids and nano-porous oxides [13, 14, 15]. Recently, for the preparation of different aluminates, garnets and superconductors we elaborated co-precipitation and ball milling process route [16, 17, 1318]. It has been noted that the ball milling process offers considerable advantages over its counterparts, such as excellent chemical homogeneity as well as better mixing of the source materials in the final product. Moreover, the molecular level mixing of the precursors to form extended networks may also enhance the structural evolution thereby lowering the crystallization temperature .
In high frequency devices, the performance of spinel ferrites can be improved by the introducing the rare earth ions in the formulation and changing the texture and structure of the product . B-sites occupied with these ions may decrease the motion of Fe2+ due to an increase in resistivity .
Metal-oxide nano particles, which differ from their bulk counterparts, recently attract the researchers due to their wide range of applications in optoelectronic industry. The unique properties of these particles also make them promising candidates for a large number of applications in recording technology as well as in biomedical . Moreover, synthesis of these spinel ferrites was the key parameter to achieve the required electrical and magnetic properties . The objective of the given work was to synthesize a sufficiently dense ferrite material by decreasing the porosity at higher temperatures and to investigate the phases developed by substituting ZnO content in the investigated materials. The fine powders of Mgx-Zn1-x-Fe2O4 ferrite were produced using co-precipitations technique followed by ball-milling and characterized for the effect of composition on their morphological and structural properties.
Materials and methods
A number of synthesis methods are being used to produce the spinel ferrites, however a standard co-precipitation technique and double sintering method were followed in the presented work. Fine particles of Mgx-Zn1-x-Fe2O4 were co-precipitated, ball milled and sintered to investigate the effect of the ferrite composition on its properties. The AR grade chemicals including hexa hydrated manganese chloride, hexa hydrated zinc chloride, hexa hydrated ferric chloride (FeCl3.6H2O), sodium hydroxide (NaOH) and acetone (CH3COCH5) were imported from Sigma- Aldrich (Germany). All the chemicals and reagents, used in the conducted research work, were of high purity. To obtain the desired ferrite composition, the salts of stoichiometric amounts of manganese chloride, zinc chloride and ferric chloride were dissolved in distilled water and subjected to magnetic stirring. The precipitant agent (NaOH) was used to attain the desired pH of the mixture. Additionally, NaOH also worked to accelerate the reaction and to limit the formation of the other non-crystalline phases.
Different samples of Mgx-Zn1-x-Fe2O4 ferrite were synthesized by varying the ‘x’ value in the composition (0.1, 0.3, 0.7, 0.75, and 0.9). The beaker containing dark brown precipitates was immersed in a pre-heated water bath. After 90 min of heat at constant temperature of 90 °C, the precipitates were settled down to the bottom of the beaker. These precipitates were filtered and washed several times with distilled water and acetone, in order to remove the sodium and chloride ions. The final product was dried for 4 h in an electric oven at heating temperature of 60 °C. The fully dried samples were grinded to obtain the desired particle size. At this end, PM400 Planetary type ball mill was used to grind the ferrite particles, as shown schematically in Figure 1. Fifty balls of four grams each were used to convert the ferrite particles into fine power. Thereafter, sintering of the precursors was carried out using double sintering technique. The source materials were initially mixed thoroughly and pre-fired twice at 600 °C. The prepared samples having different compositions were finally heated up to 800 °C for nearly 12 h and then allowed to cool down to the room temperature under ambient conditions. The sintered samples were size reduced in a ball mill operated at 35 rpm. The ratio of the steel balls to the powder was maintained as 10:1 for effective grinding . As the method for grinding is so called wet method, toluene was used as a grinding medium during ball milling. The samples were collected at periodic intervals for further analysis and characterization.
Results and discussion
Mgx-Zn1-x-Fe2O4 nanoparticles were successfully synthesized using co-precipitation technique. The concentration effect on crystal structure, crystal size, volume of the unit cell, density of the unit cell, lattice parameters and microstructures of the produced spinel ferrites was elaborated from XRD spectra and SEM micrographs. XRD spectra of Mgx-Zn1-x-Fe2O4 powders are shown in Figure 2. These spectra confirmed the formation of ferrite phases in the identified crystal structures. Sharp diffraction peaks, consistent with the face centered cubic spinel structure, were noticed in XRD patterns of the investigated samples. The lattice parameter ‘a’ was determined using the relation ‘a=d2(h2 + k2 + l2)1/2ʹ whereas X-ray density of the ferrite samples was determined using the formula ‘D=8M/Na3ʹ. In density relation, ‘M’ is the molecular weight, ‘N’ is the Avogadro’s number and ’a’ is the lattice constant of the sample. The crystal size of the ferrite samples was determined by considering the most intense diffraction peaks in XRD spectra. In this study, the Debye-Scherrer formula (T=0.9 λ/βCosθ) was used to calculate the crystal size of the tested samples. The volume of the unit cell of the synthesized samples was calculated using the respective lattice constant values. A relationship between the volume and the lattice constant existed in the form ‘V=a3ʹ.
In Figure 2, XRD patterns of MgO, ZnO and α-Fe2O3 showed only the individual reflections of the starting phase of ZnO, MgO and α-Fe2O3. However, in Mgx-Zn1-x-Fe2O4, the major ferrite phase was seen along with a small amount of α-Fe2O3 phase, which remained unreacted . In Figure 3, the broad width of the peaks revealed the growth of the ferrite phase with very small particle size. The intensity ratios of the individual reflections were in accordance with the stoichiometric composition of the mixture. The particle size reduced down sharply with an increase in peak width. The content of ZnO decreased quickly and became zero with an increase in milling time and concentration , whereas the α-Fe2O3 content exhibited slow decrease over milling time.
Peaks at 2θ of 30.55°, 35.98°, 37.52°, 43.58°, 57.66° and 63.32° were referred to XRD diffraction planes (220), (311), (222), (400), (333) and (440), respectively. These peaks confirmed the formation of cubic spinel nickel copper ferrite when compared with JCPDS card 070–2674. XRD results of calcined sample of Mgx Zn1-x Fe2O4 confirmed the ferrite phase formation with the Bragg’s angles of 31.9°, 35.7°, 36.3°, 54.2° and 56.8°. Then sample was calcined at temperature of 600 °C for one hour in a furnace for comparative phase transition studies. Five out of seven peaks revealed 71 % purity of calcined Mg0.1Zn0.9Fe2O4 ferrite and 43 % purity of uncalcined ferrite. The peaks at 35.7°, 36.4° and 62.8°, as observed in MgxZn1-xFe2O4 at x=0.3, 0.7, 0.75, 0.9, revealed that the ferrite phase dominates after calcination. The maximum purity of the sample was measured about 57 % while uncalcined sample revealed relatively lower purity of 43 %. It was due to accumulation of the energy during ball milling through repeated fragmentation and rewelding of the small grains, which led to formation of Mg–Zn ferrite phase. This phenomenon can be manifested during contraction or expansion of the lattice parameters of the above discussed phases .
Other phases have also been presented with the Bragg’s angles of 24.2°, 33.3°, 41.0°, 49.5°, 62.6° and 64.1°, which were removed by increasing the milling time . Due to high-energy impact, lattice parameter of MgO, ZnO and Fe2O3 phases came down to nanometric order within a very short duration of milling. It indicates that contamination in the sample, produced by the ball milling, was heterogeneous in nature . All MgxZn1-xFe2O4 structures, obtained with concentrations of 0.1, 0.3, 0.7, 0.75, 0.9, exhibited FCC geometry . The crystal size of the ferrite samples was determined by considering the most intense diffraction peak (311) in XRD patterns. In this study, the Debye-Scherrer formula was used to calculate the crystal size of the tested samples. The average crystal sizes were measured as 34, 54, 49, 40 and 45 nm whereas the average lattice parameter remained as 0.8 nm for all concentrations, as shown in Figure 4. The X-ray density was found in the range of 5.3–4.6 g/cm3.
A decreasing trend in crystallite size of the synthesized ferrite particles was found with an increase in concentration from 0.3 to 0.9. On increasing the value of ‘x’, Mg2+ ions in the sample and crystal size were also increased . An increase in Mg2+ ions could be attributed to the ionic size difference, since the unit cell had to expand when substituted by ions with large ionic sizes. Zn2+ ions had larger ionic radius (0.82 Å) than Mg2+ ions (0.66 Å), which when substituted reside on A-site and displaced small Fe3+ ions from A-site to B-site. MgO and ZnO were cold welded during mechanical milling and finally the crystal size was further reduced due to heating at 600 °C. The atoms were diffused and replaced by the other atoms, which have smaller ionic radii like Mg2+. This replacement resulted in a decrease in crystal size .
An increasing trend has been found in lattice parameter of ionic crystals of uncalcined samples with an increase in concentration from 0.1 to 0.7. On the other hand, a sudden decrease in lattice parameter has been observed between 0.7 and 1. This initial increment and then decrease of the crystallite size value is attributed to the well-known fracturing (reduction) and re-welding (increment) processes that happen usually in high energy ball milling. Thermal heat treatment at 600 °C for one hour grew the ferrite phase with a very high value of lattice parameter .
The X-ray density was decreased with an increase in concentration. This decrease in density was attributed to a continuous reduction in α-Fe2O3 phase content at a moderate rate during the course of milling. X-ray density of normal spinel was relatively larger than uncalcined sample and reduced slowly in the course of calcination; trend line also explained decreasing behavior. X-ray density of uncalcined samples showed a continuous behavior between concentrations of 0.1 and 0.3. Such variations in X-ray density with increasing concentration clearly indicate that if the lattice parameter increases the X-ray density will decrease . The volume of these newly grown ionic crystals in the calcined sample increases with a rise in concentration from 0.1 to 0.7. After value of 0.7 lattice parameter was suddenly dropped down and this initial reduction and then increment in the particle size is attributed to the well-known fracturing (reduction) and re-welding (increment) process that happens usually in high energy ball milling. When the sample was placed in the furnace at 600 °C, the ferrite phase grew and the value of the lattice parameter decreased. The plots in Figure 4 show that in the uncalcined sample, the ferrite phase grows with a very high value of lattice parameter and then drops due to ball milling .
Calcined ferrite samples were also analyzed by SEM technique for evaluation of their microstructures and grain size. Figure 5 shows the SEM micrographs of calcined samples: (a) Mg0.1 Zn0.9Fe2O4., (b) Mg0.3Zn0.7Fe2O4, (c) Mg0.7 Zn0.3Fe2O4, and (d) Mg0.9 Zn0.1Fe2O4. It can be observed that all the samples exhibit different grain sizes but similar grain shape. The grains are homogenously distributed. The grain size was calculated by the line intercept method and found in the range of 0.5–2 mµ, depending on the contents into the spinel lattice . Moreover, the grain size was found larger and homogenous for the ferrites, substituted with MgO and ZnO. These results are in line with XRD data where the lattice parameter values increased with increasing MgO and ZnO contents and produced larger unit cell volumes for the substituted samples. Similar types of results have been reported in literature for rare earth substituted spinel ferrites [32, 33].
The fine powders of Mgx-Zn1-x-Fe2O4 ferrite were produced, ball milled and characterized for the effect of composition on their morphological and structural properties. XRD patterns revealed the formation of impurity free single phase spinel structures of Mgx-Zn1-x-Fe2O4. The lattice parameter increased with an increase in ‘x’ content in the ferrite composition. The lattice parameters of the calcined and uncalcined ferrite samples exhibited an initial increase upto a certain value and thereafter suddenly dropped down due to fracturing and re-welding processes. Overall, the lattice parameter ‘a’ varied from 0.80 to 0.85 nm, crystallite size from 34 to 80 nm, unit cell volume from 0.528 × 10−21 to 0.62 × 10−21 cm3 and X-ray density from 5.8 to 4.5 g/cm3. The grain size was found larger and homogenous for the ferrites substituted with MgO and ZnO. X-ray density of normal spinel was relatively larger than uncalcined sample, which was reduced slowly in the course of calcination. X-ray density of uncalcined samples showed a continuous behavior between concentrations of 0.1 and 0.3. These findings suggested that the synthesized ferrites can potentially be used as core material in high frequency devices.
C. Yao, Q. Zeng, G.F. Goya, T. Torres, J. Liu, H. Wu, M. Ge, Y. Zeng, Y. Wang and J.Z. Jiang, J. Phys. Chem. C, 111 (2007) 12274–12278. Google Scholar
B.L. Yang, D.S. Cheng and S.B. Lee, Appl. Catal ., 70 (1991) 161–173. Google Scholar
Y.M. Chung, Y.T. Kwon, T.J. Kim, S.J. Lee and S.H. Oh, Catal. lett., 131 (2009) 579–586. Google Scholar
T.T. Ahmed, I.Z. Rahman and M.A. Rahman, J. mater. process. technol., 153–154 (2004) 797–803. Google Scholar
A.K.M.A. Hossain, M. Seki, T. Kawai and H. Tabata, J. appl. phys ., 96 (2004) 1273–1275. Google Scholar
P.P. Hankare, R.P. Patil, K.M. Garadkar, R. Sasikala and B.K. Chougule, Mater. res. bull., 46 (2011) 447–452. Google Scholar
V.A.M. Brabers, Chapter 3 in Handbook of Magnetic Materials edited by K. H. J Buschow, Elsevier B. V., North Holland (1995), pp. 189–324. Google Scholar
M. Niaz Akhtar, N. Yahya, A. Sattar, M. Ahmad, M. Idrees, M. Hasan Asif and M. Azhar Khan, Int. J. Appl ceram. technol. ., 12 (2015) 625–637. Google Scholar
S.H. Lee, R. Deshpande, D. Benhammou, P.A. Parilla, A.H. Mahan and A.C. Dillon, Thin solid films, 517 (2009) 3591–3595. Google Scholar
J.B. Silva, W.D. Brito and N.D.S. Mohallem, Mater. sci. eng. B, 112 (2004) 182–187. Google Scholar
S. Shukrullah, N.M. Mohamed and M.S. Shaharun, Diamond relat. mater., 58 (2015) 129–138. Google Scholar
J.M. Montes, F.G. Cuevas and J. Cintas, Appl. phys. A, 92 (2008) 375–380. Google Scholar
C.N. Chinnasamy, A. Narayanasamy, N. Ponpandian, K. Chattopadhyay, H. Guérault and J.M. Greneche, J. phys.: condens. matter ., 12 (2000) 7795. Google Scholar
D. Makovec, A. Kodre, I. Arčon and M. Drofenik, J. Nanopart. res., 13 (2010) 1781–1790. Google Scholar
S. Shukrullah, N.M. Mohamed, M.S. Shaharun and M.Y. Naz, Main group chem., 13 (2014) 251–259. Google Scholar
K. Patil, Curr. opin. solid state mater. sci ., 2 (1997) 158–165. Google Scholar
S. Bid and S.K. Pradhan, Mater. chem. phys., 82 (2003) 27–37. Google Scholar
S.A. Mazen and N.I. Abu-Elsaad, Appl. nanosci., 5 (2014) 105–114. Google Scholar
J.M. Yang and K.L. Yang, J. Nanopart. res., 11 (2008) 1739–1750. Google Scholar
I. Ahmad, T. Abbas, A.B. Ziya and A. Maqsood, Ceram. int., 40 (2014) 7941–7945. Google Scholar
D. Chen, D.Y. Li, Y.Z. Zhang and Z.T. Kang, Ultrason. sonochem., 20 (2013) 1337–1340. Google Scholar
S. Ghatak, G. Chakraborty, M. Sinha, S.K. Pradhan and A.K. Meikap, Phys. B: condens. matt., 406 (2011) 3261–3266. Google Scholar
M. Sinha and S.K. Pradhan, J. Alloy. compd ., 489 (2010) 91–98. Google Scholar
Z.V. Marinković, L. Mančić, P. Vulić and O. Milošević, J. Eur. ceram soc., 25 (2005) 2081–2084. Google Scholar
M. Kanakadurga, P. Raju and S.R. Murthy, J. Magn. Magn. Mater ., 341 (2013) 112–117. Google Scholar
T. Feczkó, A. Muskotál, L. Gál, J. Szépvölgyi, A. Sebestyén and F. Vonderviszt, J. nanopart. res., 10 (2008) 227–232. Google Scholar
K. Nadeem, S. Rahman and M. Mumtaz, Prog. nat. sci.: mater. int ., 25 (2015) 111–116. Google Scholar
A.M. Gismelseed, K.A. Mohammed, A.D. Al-Rawas, A.A. Yousif, H.M. Widatallah and M.E. Elzain, Hyperfine interact., 226 (2014) 57–63. Google Scholar
K. Maria, S. Choudhury and M. Hakim, Int. nano lett., 3 (2013) 1–10. Google Scholar
S.K. Pradhan, S. Bid, M. Gateshki and V. Petkov, Mater. chem. phys., 93 (2005) 224–230. Google Scholar
M.W. Mukhtar, M. Irfan, I. Ahmad, I. Ali, M.N. Akhtar, M.A. Khan, G. Abbas, M.U. Rana, A. Ali and M. Ahmad, J. magn. magn. mater., 381 (2015) 173–178. Google Scholar
Y.Y. Kim, B.H. Kong, M.K. Choi and H.K. Cho, Mater. sci. eng. B., 165 (2009) 80–84. Google Scholar
C. Wu, Y. Lu, D. Shen and X. Fan, Chinese sci. bull., 55 (2010) 90–93. Google Scholar
About the article
Published Online: 2017-01-27
Published in Print: 2018-01-26
The authors would like to extend their sincere appreciation to The Deanship of Scientific Research (DSR) at King Saud University, Riyadh, Saudi Arabia for supporting this work through the Research Group Project No. RG-1436-012.