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Synthesis, structural and magnetic behavior studies of Zn–Al substituted cobalt ferrite nanoparticles
Accepted Manuscript Synthesis, Structural and Magnetic behavior studies of Zn-Al substituted cobalt ferrite nanoparticles Samad Zare, Ali A. Ati, Shadab Dabagh, R.M. Rosnan, Zulkafli Othaman PII: DOI: Reference:
S0022-2860(15)00091-5 http://dx.doi.org/10.1016/j.molstruc.2015.02.006 MOLSTR 21304
To appear in:
Journal of Molecular Structure
Received Date: Revised Date: Accepted Date:
27 August 2014 15 December 2014 3 February 2015
Please cite this article as: S. Zare, A.A. Ati, S. Dabagh, R.M. Rosnan, Z. Othaman, Synthesis, Structural and Magnetic behavior studies of Zn-Al substituted cobalt ferrite nanoparticles, Journal of Molecular Structure (2015), doi: http:// dx.doi.org/10.1016/j.molstruc.2015.02.006
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Synthesis, Structural and Magnetic behavior studies of Zn-Al substituted cobalt ferrite nanoparticles Samad Zare, Ali A. Ati, Shadab Dabagh, R. M. Rosnan, Zulkafli Othaman* Ibnu Sina Institute For Fundamental Science Studies, Universiti Teknologi Malaysia, 81310 UTM Johor Bahru, Johor, Malaysia
Corresponding author Tel:+60 01127507519. E-mail address: [email protected]
Abstract A series of nano-sized Zn-Al substituted cobalt ferrite Co(1-x)Zn(x)Fe2-xAlxO4 with 0.0 ≤ x≤ 1.0 have been synthesized by chemical co-precipitation technique. The XRD spectra revealed the single phase spinel structure of Co(1-x)Zn(x)Fe2xAlxO4 with
average size of nanoparticles are estimated to be 17–30 nm. These
are small enough to achieve the suitable signal to noise ratio, which is important in the high-density recording media. The FTIR spectra show the characteristic of two strong absorption bands at 560-600 cm-1 corresponds to the intrinsic stretching vibrations of the metal at the tetrahedral site and lowest band is observed at 370-410 cm-1 corresponds to octahedral site. The crystalline structures of nanoparticles composite were characterized by Field Emission Scanning Electron Microscopy (FE-SEM). The magnetic properties such as saturation magnetization, remanence magnetization, and coercivity were calculated from the hysteresis loops. Saturation magnetization were found to increase up to x=0.4 while remanence magnetization and coercivity continuously decrease with increasing Zn–Al concentration. The stability in coercivity while increase in saturation magnetization confirms that the
Co0.6Zn0.4Fe1.6Al0.4O4 ferrite sample is suitable for applications in high-density recording media.
Keywords: Zinc-Aluminum substitution; Cobalt ferrites; Co-precipitation; nanoparticles, saturation magnetization, remanence magnetization.
1.
Introduction
Magnetic ferrite is a group of technologically important magnetic materials. For this the synthesis of nanocrystalline spinel ferrites has been intensively investigated in recent years due to potential applications in electrical components, memory devices, magnetostriction, microwave devices and highdensity magnetic recording over a wide range of frequencies because of their high resistivity and low losses [1-3]. The field of ferrites is well cultivated, due to their various potential applications and the interesting physics involved in them. The exciting magnetic and electric characters of the ferrites are found to be sensitive to their shape, size, purity and magnetic stability, which in turn are dependent on the processing conditions and different synthesis routes. Among these materials, spinel nanoferrites with formula MFe2O4 where M = Ni, Co, Zn and Mn are the most significant magnetic oxides. In spinel oxide, magnetic order depends on the competition between various kinds of super-exchange interactions among A and B site cations , i.e., JAB (A–O–B), JBB (B–O–B), and JAA (A–O–A). Certain amount of site exchange of cations is sufficient to change JAB and JBB interactions and has drastically shown different magnetic behavior in nanoparticles spinel in comparison with the bulk one [4]. In these spinels, the strong surface spin canting effect occurs when the particle size reduces to nanometer range. The competition between the disordered (canted) surface spins and the ordered core spins determines the magnetic ground state and
3
usually exhibits the decreasing of magnetization and ordering temperature in nanoparticles spinel [5]. The structural and magnetic properties of ferrites are found to be sensitive to their composition and microstructure, which in turn are dependent on the processing conditions and different synthesis routes. Recently fine particles of spinel ferrites synthesized by chemical methods were shown to have magnetic properties markedly different from those prepared by the ceramic method [6, 7]. In fact, there are numerous publications on synthesis of transition metal substituted cobalt ferrites by various methods. These various methods include, which are used for the synthesis nanosized spinel ferrite powders such as mechanical milling [8, 9], sol–gel [10-12], reverse micelle [1315], citrate–gel [16, 17] and microemulsion [18, 19], etc. However, most of these methods cannot be applied on a large scale production and noneconomical because they require expensive and often toxic reagents, complicated synthetic steps, high reaction temperature, and long reaction time. The selection of an appropriate synthetic procedure often depends on the desired properties and the final applications. Among these methods, the coprecipitation method has advantages over other methods such as free from contamination, simplicity, lower cost, more homogeneous mixing of the components and good control over the particle size of the powder. The objective of this study is to produce nano-sized cobalt ferrite powders of magnetic material and to investigate the effect of zinc aluminum substitution on the morphology, and magnetization properties of powders prepared by coperception method. The results of these investigations are analyzed in terms of powder size, surface area, mean crystalline size, and magnetization of cobalt ferrite powders. We are able to reduce the coercivity and improve the magnetic properties such as saturation magnetization and remanence.
2.
Experimental
Co(1-x)Zn(x)Fe2-xAlxO4 ferrite nanoparticles with x = 0.0, 0.2,0.4, 0.6, 0.8, 1.0 have been prepared by chemical co-precipitation route using ferric nitrate [Fe(NO3)3.9H2O](98.5%,
Merck),
zinc
nitrate
[Zn(NO3)2.6H2O](98.5%,
Merck), cobalt acetate [Co(CH3COO)2.4H2O](99%, Merck), aluminum nitrate [Al(NO3)3.9H2O] (98%, Sigma-Aldrich) and sodium hydroxide. In order to obtain
the
desired
compositions,
stoichiometric
amounts
of
Co(CH3COO)2.4H2O, Fe(NO3)3.9H2O, Zn(NO3)2.6H2O and Al(NO3)3.9H2O were dissolved in de-ionized water to prepare the solution of required concentration. These solutions were mixed in a beaker with constant stirring and heated up to 75 °C. 2M of sodium hydroxide solution was then added drop wise to the reaction mixture for precipitation while pH was kept between 11~12. Precipitates were then formed and washed several times with de-ionized water and filtered. The product was dried in an oven at a temperature of 150 °C to remove water content. These precipitates were then calcined in air at 900 °C for 10 h with a heating rate of 3 °C/min in order to examine the effects of the starting materials.
Confirmation for the formation of spinel phase and determination of its purity, were performed by X-ray diffractometer (XRD, D8 Advanced) with Cu Kα radiations as source. The 2θ scanning range was from 20o to 80o with a slow speed scanning ~2o/ min and a resolution of 0.011. Scherrer’s equation was used to determine the size of ferrite nanoparticles. Fourier transformed infrared (FTIR) spectra were recorded using Perkin Elmer 5DX FTIR after mixing 1 mg of ferrite sample with 100 mg of potassium bromide (KBr). The contents were thoroughly ground in a mortar with a pestle for 5 min until a fine mixture was obtained, which was further used to make pellets in a die of 1 cm diameter. FESEM operated at 30 kV was used to record images. The room temperature
5
magnetic properties were measured employing vibrating sample magnetometer (VSM, Lake Shore 7303-9309 VSM). Each sample with powder form was calcined for 10h at 900 oC prior to the measurement.
3.
Results and Discussion
The powder X-ray diffraction patterns of the as-prepared and calcinated Co(1x)Zn(x)Fe2-xAlxO4
samples are shown in Figure1. All the observed diffraction
peaks of ferrite samples annealed at 900 °C, are indexed on the basis of the face centered cubic unit cell (JCPDS files No.10-0325). The absence of any additional peaks indicates that the synthesized samples have single-phase cubic spinel structure [20]. The broad peaks in the XRD patterns indicate that the ferrite particles are in nanoscale. All peaks in the diffraction pattern have been indexed and the lattice parameter was refined using Powder X indexing software [21]. The crystalline size of each composition were calculated from line width of (311) peak using Scherrer’s formula after taking into account the instrumental broadening [22].
(1)
Where K is a constant taken as 0.89, λ is the wavelength of X-ray in Ǻ , β is the full width at half-maximum (FWHM) in radians in 2θ scale, θ is the Bragg angle, and DXRD is the crystallite size in nm. The average particle size was found to be in the range of 17-30 nm. Our nanoparticles were much smaller compared to those reported earlier (45–49 nm, 40 nm, 1500 nm and 92 nm) [11, 23-25] . These nanocrystallites were small enough to achieve suitable signal-tonoise ratio detrimental for high-density recording media. The lattice constant
(a), cell volume (V) and the density were calculated from the XRD spectra using the following relations [26]:
(2)
V = a3
(3)
=
య
(4)
Figure 2 presents the variation of lattice parameter as a function of substituents concentration (Zn2+ and Al3+) extracted from the XRD spectra. The increase in ‘a’ with increasing Zn-Al contents except at x=0.8 is summarized in Table 1.This increase is attributed to the preferential occupation of Zn2+ and Al3+ ions on A and B sites by replacing Fe3+ions. The decrease in ‘a’ at x=0.8 supports the assumption that more amount of Al3+ ions with smaller ionic radii (0.51 Ǻ) are entering both the A and B sites. The X-ray density as a function of Zn-Al ions content is shown in Figure 3. The decrease in X-ray density with increasing Zn-Al content is due to the small molar masses of substituent ions. From the table it is conceivable that, variation values of lattice parameters at different zinc-aluminum contents were obtained using different types of surfactant. In addition, the lattice parameter was slightly changed with increasing Zn-Al content. According to Shannon (1967) [27], the ionic radius of Zn2+ ions (0.74 Å) is slightly higher than that of Al3+ions (0.51 Å). It is well known that, Zn2+ ions have a stronger preference for the tetrahedral sites, while most of the Al3+ ions prefer to occupy the octahedral and tetrahedral sites. Fe3+ ions can distributed between both sites though they prefer the B site while, Co2+ ion exclusively occupy the octahedral site [28-30]. Thus, the subsequent replacement of iron ions of ionic radii (0.67Å) by aluminum-zinc at A and B sites, in the investigated system is expected to have slight effect on the values of the lattice parameter [27].
7
The morphology of the ferrite powder was observed by Field-Emission Scanning Electron Microscope (FE-SEM) and is presented in Figure 4. It shows the uniform nature of the ferrite particles with fine grains and some agglomeration due to the interactions of magnetic nanoparticles. The surface morphology of all the particles as seen from the FE-SEM consists of homogeneous grain distribution with relatively well crystallized grains and an average grain size smaller than 100 nm. The observed difference in particle size calculated by XRD and as observed by FE-SEM may be due to the molecular structural disorder and lattice strain, which resulted the different ionic radii and/or clustering of the nanoparticles. Particle size decreases with increasing Al3+ substitution. The reduction in particle size was may be due to the mechanically induced contraction in ferrite samples due to the deformation of Fe2+–O2-–Fe3+ [31]. The agglomeration of the particles might have resulted during annealing from the driving force provided by the net decrease in the solid–solid and the solid–vapor interface free energy provides the driving force for the grain growth during the annealing process. Another reason for the agglomeration of particles might be due to the reason that particles at nanoscale have a larger surface to volume ratio, which results in the highly interfacial surface tension. The agglomeration is the indication of high reactivity of the prepared sample with heat treatment, which may arise from the magneto-static or exchange interactions between particles. Mainly the nanoparticles tend to agglomerate when they experience of nanoparticles for a permanent magnetic moment proportional to their volume [32]. The degree of agglomeration decreases with increasing aluminum substitution which might be due to the replacement of magnetic Fe3+ ions by diamagnetic Al3+ ions in A and B sites. This then leads to the decrease in magnetic moment, which in turn decreases the grain size [29, 30]. It is known that Fe3+ and Al3+ ions distribute over A- and B-sites [33], while Zn2+ ions have strong preference for A-site [29,
30], which increase the net magnetization. However, at higher substitution level, a decrease in magnetization occurs [34]. The reason for this is that low Zn concentrations lead to a decrease in the number of spins occupying the A sublattices causing an increase in the net magnetization. As the Zn content is increased the exchange interactions are weakened and the B spins are no longer held rigidly parallel to the few remaining A spins. The decrease in the B-sublattice moment, interpreted as a spin departure from co-linearity, causing the effect known as canting. It is clear from the FE-SEM micrographs that the nanostructure changes with Zn-Al substitution. A closer look at these nanostructures has found that the grains are nearly spherical in shape.
The FTIR spectra, which help to identify the formation of spinel structure in ferrites are shown in Figure 5. The IR spectra have been used to locate the characteristic vibration frequency corresponding to Fe–O bonds in the ferrite system. The IR spectra of all the samples annealed at 900 °C exhibit two main absorption bands below 1000 cm-1, corresponding to the vibrational modes of all the spinel compounds, confirming the formation of the metal oxides [35]. The assignments for the absorption bands are summarized in Table 1. Following Waldron (1955) [36], ferrites can be described as continuously bonded crystals in which the atoms are bonded to all nearest neighbors by equivalent strength of ionic, covalent or van der Waals interactions. In ferrites, the metal ions occupy two different sub-lattices designated as tetrahedral (Asite) and octahedral (B-site) with respect to the geometrical configuration of the oxygen nearest neighbors. The observed band with higher wavenumber (ν1) in the range of 584–610 cm-1 corresponds to the intrinsic stretching vibrations of the metal at the tetrahedral site (Mtetra↔O). The other band (ν2) appears around 385–450 cm-1 is attributed to the octahedral-metal stretching (Mocta↔O) [37, 38]. The noticeable change in the band positions are the result of different Fe3+–
9
O2- ions distance associated with the octahedral and tetrahedral complexes. Interestingly, the characteristic band ν1 shows a shift towards lower frequency region with increasing substituents contents. The observed increase in the metal–oxygen stretching frequency is related to the higher atomic mass of substituents contents.
Figure 6 presents the hysteresis loops for the samples synthesized by the coprecipitation method. The narrow loops for all the samples indicate the soft nature of the ferrite nanoparticles. Various magnetic properties such as saturation magnetization (Ms), remanence (Mr) and coercivity (Hc) were calculated from the hysteresis loop and summarized in Table 2. The behavior of saturation magnetization, remanence and coercivity as a function of Zn–Al content is shown in Figure 7. The saturation magnetization for CoFe2O4 sample is found to be lower than their bulk counterpart with 93.3 emu/g for CoFe2O4 compared to 76.508 emu/g for this sample. This result is in good agreement with the observation by Lee et al. (1998) which was 76.5 emu/g [39]. Furthermore, the Ms values for the as synthesized samples are slightly greater than those obtained by Karimiet al. (2014) [40] and S T Alone et al. (2008) [41]. Furthermore, Table 3 shows the comparison of these values obtained for the cobalt ferrite prepared at various temperatures using different methods. Figure 7 (a), (b) and (c) show the variation of Hc, Mr and Ms as a function of Zn-Al contents. As the substituent concentration was increased from 0.2 to 0.4 the value of Ms was increased from 33.47 to 94.99 emu/g while Mr was increased from 9.15 to 20.14 emu/g. However, the Ms and Mr values show a decrement at x = 0.6, 0.8 and 1.0. The increase in the values of Ms and Mr can be explained on the basis of Neel’s theory and the distribution of cations at tetrahedral (A) and octahedral (B) sites as CoFe2O4 being an inverse spinel having formula (CoFe)B (Fe)A. The spins of electron at A and B sites are
antiparallel to each other that resulting in cancellation of magnetic moment. The net magnetization on sub-lattice B is higher than A [34]. The enhancement of saturation magnetization and remanence are both ascribed to the increase of unpaired electrons at B site due to the replacement of Fe3+ ion from the tetrahedral sites by nonmagnetic Al3+ ion. The sudden decrease in the Ms and Mr for x = 0.4, 0.6 and 0.8 may be related to the presence of excess nonmagnetic cation that weakens the interaction between A and B sites. The total number of unpaired electrons is reduced because the migration of Fe3+ ions towards the tetrahedral site. In addition, the change of Hc from 726.15 Oe to 98.085 Oe (Table 2) with increasing substituents concentration is originated from the decrease in the magneto-crystalline anisotropy [42]. Similar results were reported on other ferrite systems [43, 44]. The rapid drop in the values of Ms and Mr with further addition of Zn-Al is majorly attributed to the weakening of the moments on A-site to affect the moments on B-site which results in a sudden drop in the net moment by decreasing the B–B interaction [45, 46]. In addition, the initial formation of non-magnetic phase results from solid state reaction at 900 ºC is also responsible for such a decrement [47]. The particles agglomeration, as appeared from FE-SEM images, can be considered as one of the reasons that probably explain of the visual absence of any hysteresis loop for superparamagnetic particles at the room temperature range [48]. Another reason can be the effect of relaxation of particles magnetization, which has been described by Hergt (1998) [49] when the characteristic time of the measurement is much longer than the relaxation time. The low magnetization and consequently the low magnetic moment exhibited by all samples can be attributed to the larger surface-to-volume ratio. Also, the finite size effect of the nanoparticles leads to a non-colinearity or canting of spins on their surface, which leads to a spin disorder and thereby reduces the magnetization [50]. In addition, the substitution of Fe3+ ions with magnetic moment of 5 µ B replaced
11
by Al3+ ions with magnetic moment of 0 µ B, in the tetrahedral and octahedral sites, and Zn2+ ions with magnetic moment of 0 µ B replaces Fe3+ ions at tetrahedral-site, causes a lowering of the A-sublattice and B-sublattice magnetization as well as the weakening of the A–B interaction. Theses result are in agreement with the well-known tendency for a change in saturation magnetization of spinel ferrite when non-magnetic ions are substituted for cations in the tetrahedral site (Zn2+) and the (Al3+) are distributed between tetrahedral and octahedral sites. The high density recording media requires saturation magnetization as much as possible and the coercivity value as low as possible [51]. In this work, the saturation magnetization and remanence is improved and the coercivity value is also
so
much
below
600
Oe.
So
the
sample
with
composition
Co0.6Zn0.4Fe1.6Al0.4O4 can be used for applications in high density recording media.
4. Conclusion
A simple and economic co-precipitation route was employed to synthesize Co-ferrite nanoparticles. The effect of Zn-Al ions on structural and magnetic properties is reported. The ability to control the particle size, sample homogeneity and successful formation of spinel structure were confirmed by XRD analyses. The obtained spinel type of structures shows excellent crystallinity and reproducibility. The crystallite size is in the range of 17–30 nm for the Zn-Al substituted Co-ferrite and is small enough for obtaining the suitable signal-to-noise ratio in the high density recording media. The FTIR spectra consisting of two absorption bands confirm the presence of A and B sub-lattices. The room temperature ferromagnetic behaviors of Zn-Al substituted Co ferrite nanoparticles were performed by VSM measurements. The enhancement in the magnetic properties with increasing Zn-Al contents is attributed to anisotropic nature of the ions. The role played by Zn-Al ions in improving the magnetic response is explained using various mechanisms. The formation and transition of single phase spinel structure with good crystallinity was taken place at around 900 °C. The results for the achieved modification and tunable magnetic properties of the synthesized nanoparticles may be nominated for many potential applications.
Acknowledgments The authors would like to thank the Universiti Teknologi Malaysia for the funding of the project and Ibnu Sina Institute for Fundamental Science Studies and Physics Department of UTM for the technical supports.
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[40] Z. Karimi, Y. Mohammadifar, H. Shokrollahi, S.K. Asl, G. Yousefi, L. Karimi, Magnetic and structural properties of nano sized Dy-doped cobalt ferrite synthesized by co-precipitation, Journal of Magnetism and Magnetic Materials, 361 (2014) 150-156. [41] S. Alone, K. Jadhav, Structural and magnetic properties of zinc-and aluminum-substituted cobalt ferrite prepared by co-precipitation method, Pramana, 70 (2008) 173-181. [42] S. Singhal, T. Namgyal, S. Bansal, K. Chandra, Effect of Zn substitution on the magnetic properties of cobalt ferrite nano particles prepared via sol-gel route, Journal of Electromagnetic Analysis and Applications, 2 (2010) 376-381. [43] R.G. Kharabe, S.A. Jadhav, A.M. Shaikh, D.R. Patil, B.K. Chougule, Magnetic properties of mixed Li–Ni–Cd ferrites, Materials Chemistry and Physics, 72 (2001) 77-80. [44] S.A. Masti, A.K. Sharma, P.N. Vasambekar, A.S. Vaingankar, Influence of Cd2+ and Cr3+ substitutions on the magnetization and permeability of magnesium ferrites, Journal of Magnetism and Magnetic Materials, 305 (2006) 436-439. [45] M.A. Gabal, R.M. El-Shishtawy, Y.M. Al Angari, Structural and magnetic properties of nano-crystalline Ni–Zn ferrites synthesized using egg-white precursor, Journal of Magnetism and Magnetic Materials, 324 (2012) 2258-2264. [46] S.A. Mazen, N.I. Abu-Elsaad, Analogous study in low magnetic field between Cu–Ge and Cu–Si ferrites, Journal of Magnetism and Magnetic Materials, 322 (2010) 265-274. [47] N.M. Deraz, M.M. Hessien, Structural and magnetic properties of pure and doped nanocrystalline cadmium ferrite, Journal of Alloys and Compounds, 475 (2009) 832-839. [48] T.N. Brusentsova, V.D. Kuznetsov, Synthesis and investigation of magnetic properties of substituted ferrite nanoparticles of spinel system Mn1−xZnx[Fe2−yLy]O4, Journal of Magnetism and Magnetic Materials, 311 (2007) 22-25. [49] R. Hergt, W. Andra, C.G. d'Ambly, I. Hilger, W.A. Kaiser, U. Richter, H.-G. Schmidt, Physical limits of hyperthermia using magnetite fine particles, Magnetics, IEEE Transactions on, 34 (1998) 3745-3754. [50] R.H. Kodama, Magnetic nanoparticles, Journal of Magnetism and Magnetic Materials, 200 (1999) 359-372. [51] M.J. Iqbal, M.N. Ashiq, P. Hernandez-Gomez, J.M. Munoz, Magnetic, physical and electrical properties of Zr–Ni-substituted co-precipitated strontium hexaferrite nanoparticles, Scripta Materialia, 57 (2007) 1093-1096.
17 [52] U.B. Sontu, V. Yelasani, V.R.R. Musugu, Structural, electrical and magnetic characteristics of nickel substituted cobalt ferrite nano particles, synthesized by self combustion method, Journal of Magnetism and Magnetic Materials, 374 (2015) 376-380. [53] H. Malik, A. Mahmood, K. Mahmood, M.Y. Lodhi, M.F. Warsi, I. Shakir, H. Wahab, M. Asghar, M.A. Khan, Influence of cobalt substitution on the magnetic properties of zinc nanocrystals synthesized via micro-emulsion route, Ceramics International, 40 (2014) 94399444. [54] I.H. Gul, A. Maqsood, M. Naeem, M.N. Ashiq, Optical, magnetic and electrical investigation of cobalt ferrite nanoparticles synthesized by co-precipitation route, Journal of Alloys and Compounds, 507 (2010) 201-206. [55] L.J. Zhao, Q. Jiang, Effects of applied magnetic field and pressures on the magnetic properties of nanocrystalline CoFe2O4 ferrite, Journal of Magnetism and Magnetic Materials, 322 (2010) 2485-2487. [56] A.M. Ibrahim, M.M.A. El-Latif, M.M. Mahmoud, Synthesis and characterization of nanosized cobalt ferrite prepared via polyol method using conventional and microwave heating techniques, Journal of Alloys and Compounds, 506 (2010) 201-204. [57] C. Murugesan, M. Perumal, G. Chandrasekaran, Structural, dielectric and magnetic properties of cobalt ferrite prepared using auto combustion and ceramic route, Physica B: Condensed Matter, 448 (2014) 53-56.
Table caption
Table 1
Structural parameters of the synthesized Co(1-x)Zn(x)Fe2-xAlxO4 (0.0 ≤ x ≤1.0) at 900 °C temperature.
Table 2
The
room
temperature
magnetic
parameters
for
each
composition. Table 3
Saturation magnetization of CoFe2O4 synthesized by different routes.
19
Table 1
Composition
ν1(cm-1)
ν2(cm-1)
DXRD(nm)
Lattice const.(a )(Å)
Cell vol. (V)(Å3)
CoFe2O4
567.007
379.206
17.2001
8.3532
582.8524
2.9533
5.3438
Co0.8Zn0.2Fe 1.8Al 0.2O4
574.47
379.206
29.7158
8.2903
569.7846
2.9310
5.3603
Co0.6 Zn0.4Fe1.6Al0.4O4
576.02
370.41
30.6753
8.3903
590.6530
2.9664
5.0729
Co 0.4 Zn 0.6Fe1.4Al0.6O4
595.552
398.732
29.4641
8.4079
594.3778
2.9726
4.9427
Co0.2 Zn0.8Fe1.2Al 0.8O4
595.55
407.75
28.0664
8.3887
590.3152
2.9658
4.8769
ZnFeAlO4
595.55
379.20
18.1653
8.4567
604.7874
2.9898
4.6627
jump length L(Å)
X-ray density (ρx-ray)/g cm-3
Table 2 composition
Hc(Oe)
Ms(emu/g)
Mr(emu/g)
Mr/Ms
Magneton number
CoFe2O4
726.15
76.508
15.747
0.2058
3.00
Co0.8Zn0.2Fe1.8Al 0.2O4
143.15
33.478
9.158
0.2735
3.40
Co0.6 Zn0.4Fe1.6Al0.4O4
143.81
94.996
20.142
0.2120
3.80
Co0.4Zn0.6Fe1.4Al 0.6O4
109.63
88.614
13.581
0.1532
4.20
Co0.2Zn0.8Fe1.2Al 0.8O4
98.085
53.157
7.9702
0.1499
4.60
ZnFeAlO4
230.88
0.67445
33.890*10-3
50.248*10-3
5
Table 3 Synthesis route Combustion micro-emulsion Co-precipitation emulsion Polyol method
ceramic method Co-precipitation
Temperature °C 600 700 800 800 800 1150 900
Particle size(nm) 35.24 19 17 30 23 301 17.2
Saturation magnetization emu/g 60.5 21.29 61.5 62.9 51.46 66.7 76.5
References [52] [53] [54] [55] [56] [57] This study
Figure caption
Figure 1
XRD spectra for Co(1-x)Zn(x)Fe2-xAlxO4 with the Gaussian fit of the peak (311).
Figure 2
Composition dependent variation of lattice constant.
Figure 3
Plot for X-ray density against Zn2+- Al3+content (x).
Figure 4
The scanning electron micrograph of Co(1-x)Zn(x)Fe2-xAlxO4 ferrite NPs.
Figure5
FTIR spectra of Co(1-x)Zn(x)Fe2-xAlxO4 ferrite NPs at room temperature.
Figure 6
The room temperature M–H curves of Co(1-x)Zn(x)Fe2-xAlxO4 ferrite NPs.
Figure 7
Compositional variation of coercivity (a), remanent magnetization (b) and saturation magnetization (c) Of Co(1-x)Zn(x)Fe2-xAlxO4 NPs.
21
Figure 1
15 0 0
G u a s s ian fit F W H M :0 .25 ° p e ac k p o s itio n :3 5.5 3 °
10 0 0
[511]
[440]
[400]
[220]
x= 0.0
[222]
Intensity(a.u. )
[311]
In te n s ity (a .u . )
20 0 0
500 3 5 .0
3 5.5
3 6.0
36 .5
2 θ ( d egr ee )
x= 0.2 x= 0.4 x= 0.6 x= 0.8 x= 1.0
20
25
30
35
40
45
50
55
2θ(Degree)
60
65
70
75
80
O
Lattice Constant (A)
Figure 2 8.48 8.46 8.44 8.42 8.40 8.38 8.36 8.34 8.32 8.30 8.28 0.0
0.2 0.4 0.6 0.8 1.0 3+ Zn2+- Al Content (x)
23
Figure 3
5.4
Density (g/cm3)
5.3 5.2 5.1 5.0 4.9 4.8 4.7 4.6
0.0
0.2 0.4 0.6 0.8 Zn2+-Al3+ Content (x)
1.0
Figu F uree 4
X= 0.2
X= = 0..4
X= = 0..6
X= 0.8
25
Figure 5
Co(1-x)Zn(x)Fe2-xAlxO4
Intensity (a. u.)
x= 0.0
x= 0.2 x= 0.4 x= 0.6 x= 0.8 x= 1.0
1000 900 800 700 600 500 400 300 Wavenumber (cm-1)
Magnetization (emu/g)
Figure 6 120 80 40 0 -40 -80 -120 120 80 40 0 -40 -80 -120 120 80 40 0 -40 -80 -120
X= 0.0 -10000
-10000
0
10000
0
120 80 40 0 -40 X= 0.4 -80 -120 10000
X= 0.8 -10000
120 80 40 0 -40 -80 -120
0
10000
X= 0.2 -10000
0
10000
X= 0.6 -10000
0
0.8 0.4 0.0 -0.4 -0.8
10000
X= 1.0 -10000
0
10000
Applied Magnetic Field (Oe)
27
Figure 7 (a)
Coercivity Field (Oe)
800 700 600 500 400 300 200 100 0
0.0
0.2 0.4 0.6 0.8 1.0 3+ Zn2+- Al Content (x)
0.0
0.2 0.4 0.6 0.8 1.0 3+ Zn2+ - Al Content (x)
Remanence Magnetization(emu/g)
Figure 7 (b)
20 15 10 5 0
Saturation Magnetization (emu/g)
Figure 7 (c)
100 80 60 40 20 0 0.0
0.2 0.4 0.6 0.8 1.0 3+ Zn2+ - Al Content (x)
29
Highlights
1- Zn-Al substituted cobalt ferrites were prepared by co-precipitation method. 2- The effect of Zn-Al substitution on Structural and magnetic properties was studied. 3- The samples were characterized using XRD, FT-IR, FE-SEM and VSM techniques. 4- IR and XRD spectra reveals the formation of single phase cubic spinel structure. 5- Our synthesis method is simple, economic, environmental friendly and yet accurate suitable for controlled growth of high quality and stable ferrite nanoparticles.
S0022-2860(15)00091-5 http://dx.doi.org/10.1016/j.molstruc.2015.02.006 MOLSTR 21304
To appear in:
Journal of Molecular Structure
Received Date: Revised Date: Accepted Date:
27 August 2014 15 December 2014 3 February 2015
Please cite this article as: S. Zare, A.A. Ati, S. Dabagh, R.M. Rosnan, Z. Othaman, Synthesis, Structural and Magnetic behavior studies of Zn-Al substituted cobalt ferrite nanoparticles, Journal of Molecular Structure (2015), doi: http:// dx.doi.org/10.1016/j.molstruc.2015.02.006
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Synthesis, Structural and Magnetic behavior studies of Zn-Al substituted cobalt ferrite nanoparticles Samad Zare, Ali A. Ati, Shadab Dabagh, R. M. Rosnan, Zulkafli Othaman* Ibnu Sina Institute For Fundamental Science Studies, Universiti Teknologi Malaysia, 81310 UTM Johor Bahru, Johor, Malaysia
Corresponding author Tel:+60 01127507519. E-mail address: [email protected]
Abstract A series of nano-sized Zn-Al substituted cobalt ferrite Co(1-x)Zn(x)Fe2-xAlxO4 with 0.0 ≤ x≤ 1.0 have been synthesized by chemical co-precipitation technique. The XRD spectra revealed the single phase spinel structure of Co(1-x)Zn(x)Fe2xAlxO4 with
average size of nanoparticles are estimated to be 17–30 nm. These
are small enough to achieve the suitable signal to noise ratio, which is important in the high-density recording media. The FTIR spectra show the characteristic of two strong absorption bands at 560-600 cm-1 corresponds to the intrinsic stretching vibrations of the metal at the tetrahedral site and lowest band is observed at 370-410 cm-1 corresponds to octahedral site. The crystalline structures of nanoparticles composite were characterized by Field Emission Scanning Electron Microscopy (FE-SEM). The magnetic properties such as saturation magnetization, remanence magnetization, and coercivity were calculated from the hysteresis loops. Saturation magnetization were found to increase up to x=0.4 while remanence magnetization and coercivity continuously decrease with increasing Zn–Al concentration. The stability in coercivity while increase in saturation magnetization confirms that the
Co0.6Zn0.4Fe1.6Al0.4O4 ferrite sample is suitable for applications in high-density recording media.
Keywords: Zinc-Aluminum substitution; Cobalt ferrites; Co-precipitation; nanoparticles, saturation magnetization, remanence magnetization.
1.
Introduction
Magnetic ferrite is a group of technologically important magnetic materials. For this the synthesis of nanocrystalline spinel ferrites has been intensively investigated in recent years due to potential applications in electrical components, memory devices, magnetostriction, microwave devices and highdensity magnetic recording over a wide range of frequencies because of their high resistivity and low losses [1-3]. The field of ferrites is well cultivated, due to their various potential applications and the interesting physics involved in them. The exciting magnetic and electric characters of the ferrites are found to be sensitive to their shape, size, purity and magnetic stability, which in turn are dependent on the processing conditions and different synthesis routes. Among these materials, spinel nanoferrites with formula MFe2O4 where M = Ni, Co, Zn and Mn are the most significant magnetic oxides. In spinel oxide, magnetic order depends on the competition between various kinds of super-exchange interactions among A and B site cations , i.e., JAB (A–O–B), JBB (B–O–B), and JAA (A–O–A). Certain amount of site exchange of cations is sufficient to change JAB and JBB interactions and has drastically shown different magnetic behavior in nanoparticles spinel in comparison with the bulk one [4]. In these spinels, the strong surface spin canting effect occurs when the particle size reduces to nanometer range. The competition between the disordered (canted) surface spins and the ordered core spins determines the magnetic ground state and
3
usually exhibits the decreasing of magnetization and ordering temperature in nanoparticles spinel [5]. The structural and magnetic properties of ferrites are found to be sensitive to their composition and microstructure, which in turn are dependent on the processing conditions and different synthesis routes. Recently fine particles of spinel ferrites synthesized by chemical methods were shown to have magnetic properties markedly different from those prepared by the ceramic method [6, 7]. In fact, there are numerous publications on synthesis of transition metal substituted cobalt ferrites by various methods. These various methods include, which are used for the synthesis nanosized spinel ferrite powders such as mechanical milling [8, 9], sol–gel [10-12], reverse micelle [1315], citrate–gel [16, 17] and microemulsion [18, 19], etc. However, most of these methods cannot be applied on a large scale production and noneconomical because they require expensive and often toxic reagents, complicated synthetic steps, high reaction temperature, and long reaction time. The selection of an appropriate synthetic procedure often depends on the desired properties and the final applications. Among these methods, the coprecipitation method has advantages over other methods such as free from contamination, simplicity, lower cost, more homogeneous mixing of the components and good control over the particle size of the powder. The objective of this study is to produce nano-sized cobalt ferrite powders of magnetic material and to investigate the effect of zinc aluminum substitution on the morphology, and magnetization properties of powders prepared by coperception method. The results of these investigations are analyzed in terms of powder size, surface area, mean crystalline size, and magnetization of cobalt ferrite powders. We are able to reduce the coercivity and improve the magnetic properties such as saturation magnetization and remanence.
2.
Experimental
Co(1-x)Zn(x)Fe2-xAlxO4 ferrite nanoparticles with x = 0.0, 0.2,0.4, 0.6, 0.8, 1.0 have been prepared by chemical co-precipitation route using ferric nitrate [Fe(NO3)3.9H2O](98.5%,
Merck),
zinc
nitrate
[Zn(NO3)2.6H2O](98.5%,
Merck), cobalt acetate [Co(CH3COO)2.4H2O](99%, Merck), aluminum nitrate [Al(NO3)3.9H2O] (98%, Sigma-Aldrich) and sodium hydroxide. In order to obtain
the
desired
compositions,
stoichiometric
amounts
of
Co(CH3COO)2.4H2O, Fe(NO3)3.9H2O, Zn(NO3)2.6H2O and Al(NO3)3.9H2O were dissolved in de-ionized water to prepare the solution of required concentration. These solutions were mixed in a beaker with constant stirring and heated up to 75 °C. 2M of sodium hydroxide solution was then added drop wise to the reaction mixture for precipitation while pH was kept between 11~12. Precipitates were then formed and washed several times with de-ionized water and filtered. The product was dried in an oven at a temperature of 150 °C to remove water content. These precipitates were then calcined in air at 900 °C for 10 h with a heating rate of 3 °C/min in order to examine the effects of the starting materials.
Confirmation for the formation of spinel phase and determination of its purity, were performed by X-ray diffractometer (XRD, D8 Advanced) with Cu Kα radiations as source. The 2θ scanning range was from 20o to 80o with a slow speed scanning ~2o/ min and a resolution of 0.011. Scherrer’s equation was used to determine the size of ferrite nanoparticles. Fourier transformed infrared (FTIR) spectra were recorded using Perkin Elmer 5DX FTIR after mixing 1 mg of ferrite sample with 100 mg of potassium bromide (KBr). The contents were thoroughly ground in a mortar with a pestle for 5 min until a fine mixture was obtained, which was further used to make pellets in a die of 1 cm diameter. FESEM operated at 30 kV was used to record images. The room temperature
5
magnetic properties were measured employing vibrating sample magnetometer (VSM, Lake Shore 7303-9309 VSM). Each sample with powder form was calcined for 10h at 900 oC prior to the measurement.
3.
Results and Discussion
The powder X-ray diffraction patterns of the as-prepared and calcinated Co(1x)Zn(x)Fe2-xAlxO4
samples are shown in Figure1. All the observed diffraction
peaks of ferrite samples annealed at 900 °C, are indexed on the basis of the face centered cubic unit cell (JCPDS files No.10-0325). The absence of any additional peaks indicates that the synthesized samples have single-phase cubic spinel structure [20]. The broad peaks in the XRD patterns indicate that the ferrite particles are in nanoscale. All peaks in the diffraction pattern have been indexed and the lattice parameter was refined using Powder X indexing software [21]. The crystalline size of each composition were calculated from line width of (311) peak using Scherrer’s formula after taking into account the instrumental broadening [22].
(1)
Where K is a constant taken as 0.89, λ is the wavelength of X-ray in Ǻ , β is the full width at half-maximum (FWHM) in radians in 2θ scale, θ is the Bragg angle, and DXRD is the crystallite size in nm. The average particle size was found to be in the range of 17-30 nm. Our nanoparticles were much smaller compared to those reported earlier (45–49 nm, 40 nm, 1500 nm and 92 nm) [11, 23-25] . These nanocrystallites were small enough to achieve suitable signal-tonoise ratio detrimental for high-density recording media. The lattice constant
(a), cell volume (V) and the density were calculated from the XRD spectra using the following relations [26]:
(2)
V = a3
(3)
=
య
(4)
Figure 2 presents the variation of lattice parameter as a function of substituents concentration (Zn2+ and Al3+) extracted from the XRD spectra. The increase in ‘a’ with increasing Zn-Al contents except at x=0.8 is summarized in Table 1.This increase is attributed to the preferential occupation of Zn2+ and Al3+ ions on A and B sites by replacing Fe3+ions. The decrease in ‘a’ at x=0.8 supports the assumption that more amount of Al3+ ions with smaller ionic radii (0.51 Ǻ) are entering both the A and B sites. The X-ray density as a function of Zn-Al ions content is shown in Figure 3. The decrease in X-ray density with increasing Zn-Al content is due to the small molar masses of substituent ions. From the table it is conceivable that, variation values of lattice parameters at different zinc-aluminum contents were obtained using different types of surfactant. In addition, the lattice parameter was slightly changed with increasing Zn-Al content. According to Shannon (1967) [27], the ionic radius of Zn2+ ions (0.74 Å) is slightly higher than that of Al3+ions (0.51 Å). It is well known that, Zn2+ ions have a stronger preference for the tetrahedral sites, while most of the Al3+ ions prefer to occupy the octahedral and tetrahedral sites. Fe3+ ions can distributed between both sites though they prefer the B site while, Co2+ ion exclusively occupy the octahedral site [28-30]. Thus, the subsequent replacement of iron ions of ionic radii (0.67Å) by aluminum-zinc at A and B sites, in the investigated system is expected to have slight effect on the values of the lattice parameter [27].
7
The morphology of the ferrite powder was observed by Field-Emission Scanning Electron Microscope (FE-SEM) and is presented in Figure 4. It shows the uniform nature of the ferrite particles with fine grains and some agglomeration due to the interactions of magnetic nanoparticles. The surface morphology of all the particles as seen from the FE-SEM consists of homogeneous grain distribution with relatively well crystallized grains and an average grain size smaller than 100 nm. The observed difference in particle size calculated by XRD and as observed by FE-SEM may be due to the molecular structural disorder and lattice strain, which resulted the different ionic radii and/or clustering of the nanoparticles. Particle size decreases with increasing Al3+ substitution. The reduction in particle size was may be due to the mechanically induced contraction in ferrite samples due to the deformation of Fe2+–O2-–Fe3+ [31]. The agglomeration of the particles might have resulted during annealing from the driving force provided by the net decrease in the solid–solid and the solid–vapor interface free energy provides the driving force for the grain growth during the annealing process. Another reason for the agglomeration of particles might be due to the reason that particles at nanoscale have a larger surface to volume ratio, which results in the highly interfacial surface tension. The agglomeration is the indication of high reactivity of the prepared sample with heat treatment, which may arise from the magneto-static or exchange interactions between particles. Mainly the nanoparticles tend to agglomerate when they experience of nanoparticles for a permanent magnetic moment proportional to their volume [32]. The degree of agglomeration decreases with increasing aluminum substitution which might be due to the replacement of magnetic Fe3+ ions by diamagnetic Al3+ ions in A and B sites. This then leads to the decrease in magnetic moment, which in turn decreases the grain size [29, 30]. It is known that Fe3+ and Al3+ ions distribute over A- and B-sites [33], while Zn2+ ions have strong preference for A-site [29,
30], which increase the net magnetization. However, at higher substitution level, a decrease in magnetization occurs [34]. The reason for this is that low Zn concentrations lead to a decrease in the number of spins occupying the A sublattices causing an increase in the net magnetization. As the Zn content is increased the exchange interactions are weakened and the B spins are no longer held rigidly parallel to the few remaining A spins. The decrease in the B-sublattice moment, interpreted as a spin departure from co-linearity, causing the effect known as canting. It is clear from the FE-SEM micrographs that the nanostructure changes with Zn-Al substitution. A closer look at these nanostructures has found that the grains are nearly spherical in shape.
The FTIR spectra, which help to identify the formation of spinel structure in ferrites are shown in Figure 5. The IR spectra have been used to locate the characteristic vibration frequency corresponding to Fe–O bonds in the ferrite system. The IR spectra of all the samples annealed at 900 °C exhibit two main absorption bands below 1000 cm-1, corresponding to the vibrational modes of all the spinel compounds, confirming the formation of the metal oxides [35]. The assignments for the absorption bands are summarized in Table 1. Following Waldron (1955) [36], ferrites can be described as continuously bonded crystals in which the atoms are bonded to all nearest neighbors by equivalent strength of ionic, covalent or van der Waals interactions. In ferrites, the metal ions occupy two different sub-lattices designated as tetrahedral (Asite) and octahedral (B-site) with respect to the geometrical configuration of the oxygen nearest neighbors. The observed band with higher wavenumber (ν1) in the range of 584–610 cm-1 corresponds to the intrinsic stretching vibrations of the metal at the tetrahedral site (Mtetra↔O). The other band (ν2) appears around 385–450 cm-1 is attributed to the octahedral-metal stretching (Mocta↔O) [37, 38]. The noticeable change in the band positions are the result of different Fe3+–
9
O2- ions distance associated with the octahedral and tetrahedral complexes. Interestingly, the characteristic band ν1 shows a shift towards lower frequency region with increasing substituents contents. The observed increase in the metal–oxygen stretching frequency is related to the higher atomic mass of substituents contents.
Figure 6 presents the hysteresis loops for the samples synthesized by the coprecipitation method. The narrow loops for all the samples indicate the soft nature of the ferrite nanoparticles. Various magnetic properties such as saturation magnetization (Ms), remanence (Mr) and coercivity (Hc) were calculated from the hysteresis loop and summarized in Table 2. The behavior of saturation magnetization, remanence and coercivity as a function of Zn–Al content is shown in Figure 7. The saturation magnetization for CoFe2O4 sample is found to be lower than their bulk counterpart with 93.3 emu/g for CoFe2O4 compared to 76.508 emu/g for this sample. This result is in good agreement with the observation by Lee et al. (1998) which was 76.5 emu/g [39]. Furthermore, the Ms values for the as synthesized samples are slightly greater than those obtained by Karimiet al. (2014) [40] and S T Alone et al. (2008) [41]. Furthermore, Table 3 shows the comparison of these values obtained for the cobalt ferrite prepared at various temperatures using different methods. Figure 7 (a), (b) and (c) show the variation of Hc, Mr and Ms as a function of Zn-Al contents. As the substituent concentration was increased from 0.2 to 0.4 the value of Ms was increased from 33.47 to 94.99 emu/g while Mr was increased from 9.15 to 20.14 emu/g. However, the Ms and Mr values show a decrement at x = 0.6, 0.8 and 1.0. The increase in the values of Ms and Mr can be explained on the basis of Neel’s theory and the distribution of cations at tetrahedral (A) and octahedral (B) sites as CoFe2O4 being an inverse spinel having formula (CoFe)B (Fe)A. The spins of electron at A and B sites are
antiparallel to each other that resulting in cancellation of magnetic moment. The net magnetization on sub-lattice B is higher than A [34]. The enhancement of saturation magnetization and remanence are both ascribed to the increase of unpaired electrons at B site due to the replacement of Fe3+ ion from the tetrahedral sites by nonmagnetic Al3+ ion. The sudden decrease in the Ms and Mr for x = 0.4, 0.6 and 0.8 may be related to the presence of excess nonmagnetic cation that weakens the interaction between A and B sites. The total number of unpaired electrons is reduced because the migration of Fe3+ ions towards the tetrahedral site. In addition, the change of Hc from 726.15 Oe to 98.085 Oe (Table 2) with increasing substituents concentration is originated from the decrease in the magneto-crystalline anisotropy [42]. Similar results were reported on other ferrite systems [43, 44]. The rapid drop in the values of Ms and Mr with further addition of Zn-Al is majorly attributed to the weakening of the moments on A-site to affect the moments on B-site which results in a sudden drop in the net moment by decreasing the B–B interaction [45, 46]. In addition, the initial formation of non-magnetic phase results from solid state reaction at 900 ºC is also responsible for such a decrement [47]. The particles agglomeration, as appeared from FE-SEM images, can be considered as one of the reasons that probably explain of the visual absence of any hysteresis loop for superparamagnetic particles at the room temperature range [48]. Another reason can be the effect of relaxation of particles magnetization, which has been described by Hergt (1998) [49] when the characteristic time of the measurement is much longer than the relaxation time. The low magnetization and consequently the low magnetic moment exhibited by all samples can be attributed to the larger surface-to-volume ratio. Also, the finite size effect of the nanoparticles leads to a non-colinearity or canting of spins on their surface, which leads to a spin disorder and thereby reduces the magnetization [50]. In addition, the substitution of Fe3+ ions with magnetic moment of 5 µ B replaced
11
by Al3+ ions with magnetic moment of 0 µ B, in the tetrahedral and octahedral sites, and Zn2+ ions with magnetic moment of 0 µ B replaces Fe3+ ions at tetrahedral-site, causes a lowering of the A-sublattice and B-sublattice magnetization as well as the weakening of the A–B interaction. Theses result are in agreement with the well-known tendency for a change in saturation magnetization of spinel ferrite when non-magnetic ions are substituted for cations in the tetrahedral site (Zn2+) and the (Al3+) are distributed between tetrahedral and octahedral sites. The high density recording media requires saturation magnetization as much as possible and the coercivity value as low as possible [51]. In this work, the saturation magnetization and remanence is improved and the coercivity value is also
so
much
below
600
Oe.
So
the
sample
with
composition
Co0.6Zn0.4Fe1.6Al0.4O4 can be used for applications in high density recording media.
4. Conclusion
A simple and economic co-precipitation route was employed to synthesize Co-ferrite nanoparticles. The effect of Zn-Al ions on structural and magnetic properties is reported. The ability to control the particle size, sample homogeneity and successful formation of spinel structure were confirmed by XRD analyses. The obtained spinel type of structures shows excellent crystallinity and reproducibility. The crystallite size is in the range of 17–30 nm for the Zn-Al substituted Co-ferrite and is small enough for obtaining the suitable signal-to-noise ratio in the high density recording media. The FTIR spectra consisting of two absorption bands confirm the presence of A and B sub-lattices. The room temperature ferromagnetic behaviors of Zn-Al substituted Co ferrite nanoparticles were performed by VSM measurements. The enhancement in the magnetic properties with increasing Zn-Al contents is attributed to anisotropic nature of the ions. The role played by Zn-Al ions in improving the magnetic response is explained using various mechanisms. The formation and transition of single phase spinel structure with good crystallinity was taken place at around 900 °C. The results for the achieved modification and tunable magnetic properties of the synthesized nanoparticles may be nominated for many potential applications.
Acknowledgments The authors would like to thank the Universiti Teknologi Malaysia for the funding of the project and Ibnu Sina Institute for Fundamental Science Studies and Physics Department of UTM for the technical supports.
References
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Table caption
Table 1
Structural parameters of the synthesized Co(1-x)Zn(x)Fe2-xAlxO4 (0.0 ≤ x ≤1.0) at 900 °C temperature.
Table 2
The
room
temperature
magnetic
parameters
for
each
composition. Table 3
Saturation magnetization of CoFe2O4 synthesized by different routes.
19
Table 1
Composition
ν1(cm-1)
ν2(cm-1)
DXRD(nm)
Lattice const.(a )(Å)
Cell vol. (V)(Å3)
CoFe2O4
567.007
379.206
17.2001
8.3532
582.8524
2.9533
5.3438
Co0.8Zn0.2Fe 1.8Al 0.2O4
574.47
379.206
29.7158
8.2903
569.7846
2.9310
5.3603
Co0.6 Zn0.4Fe1.6Al0.4O4
576.02
370.41
30.6753
8.3903
590.6530
2.9664
5.0729
Co 0.4 Zn 0.6Fe1.4Al0.6O4
595.552
398.732
29.4641
8.4079
594.3778
2.9726
4.9427
Co0.2 Zn0.8Fe1.2Al 0.8O4
595.55
407.75
28.0664
8.3887
590.3152
2.9658
4.8769
ZnFeAlO4
595.55
379.20
18.1653
8.4567
604.7874
2.9898
4.6627
jump length L(Å)
X-ray density (ρx-ray)/g cm-3
Table 2 composition
Hc(Oe)
Ms(emu/g)
Mr(emu/g)
Mr/Ms
Magneton number
CoFe2O4
726.15
76.508
15.747
0.2058
3.00
Co0.8Zn0.2Fe1.8Al 0.2O4
143.15
33.478
9.158
0.2735
3.40
Co0.6 Zn0.4Fe1.6Al0.4O4
143.81
94.996
20.142
0.2120
3.80
Co0.4Zn0.6Fe1.4Al 0.6O4
109.63
88.614
13.581
0.1532
4.20
Co0.2Zn0.8Fe1.2Al 0.8O4
98.085
53.157
7.9702
0.1499
4.60
ZnFeAlO4
230.88
0.67445
33.890*10-3
50.248*10-3
5
Table 3 Synthesis route Combustion micro-emulsion Co-precipitation emulsion Polyol method
ceramic method Co-precipitation
Temperature °C 600 700 800 800 800 1150 900
Particle size(nm) 35.24 19 17 30 23 301 17.2
Saturation magnetization emu/g 60.5 21.29 61.5 62.9 51.46 66.7 76.5
References [52] [53] [54] [55] [56] [57] This study
Figure caption
Figure 1
XRD spectra for Co(1-x)Zn(x)Fe2-xAlxO4 with the Gaussian fit of the peak (311).
Figure 2
Composition dependent variation of lattice constant.
Figure 3
Plot for X-ray density against Zn2+- Al3+content (x).
Figure 4
The scanning electron micrograph of Co(1-x)Zn(x)Fe2-xAlxO4 ferrite NPs.
Figure5
FTIR spectra of Co(1-x)Zn(x)Fe2-xAlxO4 ferrite NPs at room temperature.
Figure 6
The room temperature M–H curves of Co(1-x)Zn(x)Fe2-xAlxO4 ferrite NPs.
Figure 7
Compositional variation of coercivity (a), remanent magnetization (b) and saturation magnetization (c) Of Co(1-x)Zn(x)Fe2-xAlxO4 NPs.
21
Figure 1
15 0 0
G u a s s ian fit F W H M :0 .25 ° p e ac k p o s itio n :3 5.5 3 °
10 0 0
[511]
[440]
[400]
[220]
x= 0.0
[222]
Intensity(a.u. )
[311]
In te n s ity (a .u . )
20 0 0
500 3 5 .0
3 5.5
3 6.0
36 .5
2 θ ( d egr ee )
x= 0.2 x= 0.4 x= 0.6 x= 0.8 x= 1.0
20
25
30
35
40
45
50
55
2θ(Degree)
60
65
70
75
80
O
Lattice Constant (A)
Figure 2 8.48 8.46 8.44 8.42 8.40 8.38 8.36 8.34 8.32 8.30 8.28 0.0
0.2 0.4 0.6 0.8 1.0 3+ Zn2+- Al Content (x)
23
Figure 3
5.4
Density (g/cm3)
5.3 5.2 5.1 5.0 4.9 4.8 4.7 4.6
0.0
0.2 0.4 0.6 0.8 Zn2+-Al3+ Content (x)
1.0
Figu F uree 4
X= 0.2
X= = 0..4
X= = 0..6
X= 0.8
25
Figure 5
Co(1-x)Zn(x)Fe2-xAlxO4
Intensity (a. u.)
x= 0.0
x= 0.2 x= 0.4 x= 0.6 x= 0.8 x= 1.0
1000 900 800 700 600 500 400 300 Wavenumber (cm-1)
Magnetization (emu/g)
Figure 6 120 80 40 0 -40 -80 -120 120 80 40 0 -40 -80 -120 120 80 40 0 -40 -80 -120
X= 0.0 -10000
-10000
0
10000
0
120 80 40 0 -40 X= 0.4 -80 -120 10000
X= 0.8 -10000
120 80 40 0 -40 -80 -120
0
10000
X= 0.2 -10000
0
10000
X= 0.6 -10000
0
0.8 0.4 0.0 -0.4 -0.8
10000
X= 1.0 -10000
0
10000
Applied Magnetic Field (Oe)
27
Figure 7 (a)
Coercivity Field (Oe)
800 700 600 500 400 300 200 100 0
0.0
0.2 0.4 0.6 0.8 1.0 3+ Zn2+- Al Content (x)
0.0
0.2 0.4 0.6 0.8 1.0 3+ Zn2+ - Al Content (x)
Remanence Magnetization(emu/g)
Figure 7 (b)
20 15 10 5 0
Saturation Magnetization (emu/g)
Figure 7 (c)
100 80 60 40 20 0 0.0
0.2 0.4 0.6 0.8 1.0 3+ Zn2+ - Al Content (x)
29
Highlights
1- Zn-Al substituted cobalt ferrites were prepared by co-precipitation method. 2- The effect of Zn-Al substitution on Structural and magnetic properties was studied. 3- The samples were characterized using XRD, FT-IR, FE-SEM and VSM techniques. 4- IR and XRD spectra reveals the formation of single phase cubic spinel structure. 5- Our synthesis method is simple, economic, environmental friendly and yet accurate suitable for controlled growth of high quality and stable ferrite nanoparticles.