- Email: [email protected]
Effect of Mg substitution on the magnetic properties of NiCuZn ferrite nanoparticles prepared through a novel method using egg white
ARTICLE IN PRESS Journal of Magnetism and Magnetic Materials 321 (2009) 3144–3148
Contents lists available at ScienceDirect
Journal of Magnetism and Magnetic Materials journal homepage: www.elsevier.com/locate/jmmm
Effect of Mg substitution on the magnetic properties of NiCuZn ferrite nanoparticles prepared through a novel method using egg white M.A. Gabal Chemistry Department, Faculty of Science, King Abdul Aziz University, Jeddah, Saudi Arabia
a r t i c l e in f o
a b s t r a c t
Article history: Received 17 March 2009 Received in revised form 19 April 2009 Available online 29 May 2009
Nanocrystalline Mg-substituted NiCuZn ferrites were successfully synthesized, for the first time, by using metal nitrates and freshly extracted egg white. The thermal decomposition process of the nitrate–egg white precursors was investigated by thermogravimetric (TG) technique. X-ray diffraction (XRD) revealed that, single-phase cubic ferrites with average particle size of 23.9–35.1 nm were directly formed after ignition at 500 1C. No noticeable variation of lattice parameters with increasing magnesium content was observed, while X-ray densities were found to decrease. This can be explained on the basis of ionic radii and atomic masses of the substituted cation. Transmission electron microscope (TEM) shows that, particles are permanently magnetized and get agglomerated. The saturation magnetization (Ms) and coercivity (Hc) as a function of Mg content were investigated using vibrating sample magnetometer (VSM). It has been found that the Ms increases firstly up to x ¼ 0.2 and then decreases, while Hc continuously decreases. Magnetic susceptibility measurements give results which agree well with those obtained by VSM. The obvious decrease in the Curie temperature (TC) with increasing Mg indicates that the ferrimagnetic grains are widely separated and enclosed by nonmagnetic magnesium ions. & 2009 Elsevier B.V. All rights reserved.
Keywords: Mg substitution NiCuZn ferrite Egg white XRD VSM Susceptibility
1. Introduction With the rapid development of mobile communication and information technology, electronic components with small size, high efficiency and low cost are urgently demanded [1]. Multilayer chip inductor (MLCI) is a passive surface mount device widely used in electronic products, such as cellular phone, notebook computer and video cameras. Up to now, Ni–Cu–Zn ferrites have been the dominant materials for MLCI due to their better magnetic properties at high frequency and low sintering temperature [2]. Since silver (internal conductor) has a melting point of 961 1C, a much lower (o961 1C) sintering temperature of ferrite is preferred to suppress the diffusion of silver metal into the ferrite core. This metal diffusion into the ferrite body decreases the resistivity of the core. NiCuZn ferrite was usually prepared by the conventional ceramic method but the resultant products are not necessarily always stoichiometric or homogeneous [3]. Many new methods were tried to prepare the low firing temperature NiCuZn ferrite, of which the sol–gel self-propagating method was one [4]. The process has the advantages of being able to use inexpensive
Corresponding author. Permanent address: Chemistry Department, Faculty of Science, Benha University, Benha, Egypt. Tel.: +00966557071572. E-mail address: [email protected]
0304-8853/$ - see front matter & 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.jmmm.2009.05.047
precursors and a simple preparation method that results in nano-sized, homogeneous, highly reactive powder. In the present work, we tried to find simple and cost-effective routes to synthesize nanocrystalline NiCuZn ferrites by the utilization of cheap, nontoxic and environmentally benign precursors. Egg white proteins are well known for their gelling, foaming and emulsifying characteristics, in addition to their high nutrition quality [5]. Due to its solubility in water and its ability to associate with metal ions in solution, egg white has been used as a binder cum gel for shaping material, particularly bulk and porous ceramics [6]. The use of egg white simplifies the process and would provide another alternative process for the simple and economical synthesis of NiCuZn ferrites. Few studies on the electromagnetic properties of Mg-doped NiCuZn ferrites are present in the literature. Ni0.25xMgxCu0.2 Zn0.55Fe2O4 with x ¼ 0.0, 0.07, 0.13, 0.18 and 0.25 was synthesized through nitrate–citrate auto-combustion method [7]. The asburnt powders showed crystalline cubic spinel ferrite with about 19–22 nm crystallite sizes. The permeability and AC resistivity were found to increase and the magnetic loss decreased with Mg substitution. The composition with x ¼ 0.18 was found to be better than NiCuZn-based material for more miniaturization of MLCI. Mg-containing NiCuZn ferrites are preferred to avoid the presence of divalent iron and to avoid the tendency of discontinuous grain growth. Also the Mg substitution in NiCuZn ferrite was
ARTICLE IN PRESS M.A. Gabal / Journal of Magnetism and Magnetic Materials 321 (2009) 3144–3148
100 80 Mass loss (%)
found to improve its magnetic properties [7]. In addition, the preparation method is expected to play an important role on the different properties. Based on this, the present work is aiming at the investigation of the effect of Mg substitution for Ni on the magnetic properties of nano-sized Ni0.5xCu0.2Zn0.3MgxFe2O4 system, prepared at low temperature through a novel method using metal nitrate and egg white. So far to the knowledge of researchers, no literatures are available on this aspect.
3. Results and discussion 3.1. Thermal analysis studies Fig. 1. shows TG curves for pure egg white and the dried nitrate–egg white precursor (with magnesium content of 0.3). The curves show that, the decomposition rapidly propagated forward until all egg white was completely burnt out at about 500 1C. Accordingly, this temperature can be taken as the appropriate temperature for calcining the mixture. 3.2. Structural studies X-ray diffraction patterns of the as-prepared Ni0.5x Cu0.2Zn0.3MgxFe2O4 system show completely amorphous behavior of the materials. When the sintering temperature was increased to 500 1C, broad peaks corresponding to single-phase cubic spinel
60 40 Precursor
2. Experimental procedure
20 Pure egg-white
0
100
200
300 400 Temperature (°C)
500
600
Fig. 1. TG curves in air of pure egg white and precursor with Mg content of 0.3. Heating rate ¼ 5 1C min1.
(311)
(220)
Intensity (arb. units)
Ferrite powders of compositions; Ni0.5xCu0.2Zn0.3MgxFe2O4 (0.0rxr0.4) were prepared using ferric nitrate, zinc nitrate, nickel nitrate, magnesium nitrate and copper nitrate with high chemical purity. The stoichiometric amounts of metal nitrates were dissolved together in a minimum amount of doubly distilled water to get a clear solution. 60 ml of extracted egg white, dissolved in 40 ml of bi-distilled water through vigorous stirring, was added to the nitrate mixture at room temperature. After constant stirring for 30 min, the resultant sol–gel was evaporated at 80 1C until a dry precursor was obtained. Based on the thermal analysis measurements, the obtained precursors were calcined in an electric muffle at 500 1C for 1 h. Thermogravimetric (TG) analysis was carried out, using PerkinElmer thermal analyzer on precursors up to 850 1C at a heating rate of 5 1C min1. The sample mass in the Pt crucible was 10 mg. The phase identification of the as-burnt and calcined powders was performed by X-ray diffraction (XRD) on D8 Advance diffractometer (Bruker AXS, Germany) using Cu Ka1 radiation (l ¼ 1.5405 A˚). The average crystallite size of the synthesized powders was determined by X-ray line broadening technique using the well-known Scherrer formula [8]. Fourier transform infrared (FT-IR) spectroscopic analysis using KBr pellets was carried out using a Jasco model FT-IR 310 spectrophotometer. Transmission electron microscopy (TEM) was carried out on a JEOL 2010 transmission electron microscope with an accelerating voltage of 100 kV. A vibrating sample magnetometer (VSM) was used to measure the saturation magnetization (Ms) and intrinsic coercive force (Hc) of the annealed powders at room temperature. An applied magnetic field of 5 kOe to reach saturation values was used. The magnetic susceptibility of the investigated samples at different temperatures as a function of different magnetic field intensities was measured using Faraday’s method, in which the sample was inserted at the point of maximum force.
3145
(440)
(511) (222)
(400)
(422)
x = 0.4 x = 0.3 x = 0.2 x = 0.1
x = 0.0
20
30
40
50
60
70
2θ (deg) Fig. 2. Characteristic parts of XRD patterns of Ni0.5xCu0.2Zn0.3MgxFe2O4 system.
ferrite appeared (Fig. 2). The broadness of these peaks indicates the nanocrystalline nature of these ferrites. The lattice parameter, X-ray density and average crystallite size for the different samples are presented in Table 1. No noticeable variation of lattice parameters with increasing magnesium content was observed. This can be explained in terms of the ionic radii, where the difference in the ionic radii of Mg2+ (0.72 A˚) and Ni2+ (0.69 A˚) is small [9]. A similar behavior was reported by Roy and Bera for Mgsubstituted NiCuZn ferrite prepared through auto-combustion method [7]. The decrease in the X-ray density with increasing Mg content can be attributed to the substitution of heavier nickel atom by the lighter magnesium atom. This decrease in weight with constant size causes a decrease in the X-ray density. The average crystallite size of the ferrites is in the range 23.9–35.1 nm. It increases slightly with increasing Mg content up to x ¼ 0.2 and then decreases. FT-IR spectral data of Ni0.5xCu0.2Zn0.3MgxFe2O4 system calcined at 500 1C are shown in Table 1. In ferrite the metal cations are situated according to the geometric configuration of the oxygen ion nearest neighbors, in two different sub-lattices such as tetrahedral (A-sites) and octahedral (B-sites). The band n1 around 600 cm1 is attributed to stretching vibration of tetrahedral complexes and n2 around 400 cm1 to that of octahedral complexes [10]. The data in the table revealed that n1 and n2 are nearly constant with the addition of Mg. The slight decreases in the value of n2 from 412 cm–1 for the sample without Mg content to 401 cm–1 for that rich with magnesium can be attributed to the
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Table 1 Lattice parameters, X-ray densities, average crystallite size, FT-IR spectral data and magnetic data of Ni0.5xCu0.2Zn0.3MgxFe2O4 system. Parameters
x ¼ 0.0
x ¼ 0.1
x ¼ 0.2
x ¼ 0.3
x ¼ 0.4
Lattice parameter, a (A˚) X-ray density, Dx (g cm3) Average crystallite size, L (nm) Tetrahedral vibration, n1 (cm1) Octahedral vibration, n2 (cm1) Saturation magnetization, Ms (emu g1) Remenant magnetization, Mr (emu g1) Corecivity, Hc (emu g1) Magnetic moment, ZB (mB) Molar magnetic Susceptibility, wM (emu g1 mole1) Curie temperature, Tc (K) Curie constant, C (emu g1 mole1) Effective magnetic moment, meff (mB)
8.389 5.34 35.1 584 412 40.54 8.06 67.33 1.72 7.4 768 2.92 4.83
8.387 5.27 38.0 585 410 42.71 8.35 50.85 1.79 7.3 712 11.97 9.71
8.391 5.19 42.1 585 407 45.25 9.27 43.46 1.87 5.8 654 12.3 9.92
8.385 5.12 32.9 582 403 39.61 6.44 31.34 1.61 5.6 600 10.59 9.21
8.398 5.02 23.9 583 401 35.95 5.88 14.63 1.44 4.4 577 9.41 8.68
Magnetic field strength (Oe)
50
25
0
-25
-50 -2000
Fig. 3. TEM image of the sample with Mg content of 0.1.
tendency of magnesium ions, with slightly higher ionic radius than nickel, to occupy the octahedral site. 3.2. Morphological studies The TEM image of the sample with Mg content of 0.1 is shown in Fig. 3. The image illustrates the nanoscale nature of ferrite particles. Agglomerated particles as well as separated ones are present in the sample. Mainly the nanoparticles tend to agglomerate because they experience a permanent magnetic moment proportional to their volume [11]. Hence, each particle is permanently magnetized and gets agglomerated. The agglomeration can also be attributed, to a minor extent, to electrostatic or Van der Walls forces between particles. The image also shows that the particles are mostly in the 38–40 nm size range, which corroborates well with the XRD investigation. The shape of the majority of the nanoparticles appears spherical; however, some particles with straight edges are also present. 3.3. Magnetic properties studies 3.3.1. Hysteresis behavior The hysteresis loops of the investigated samples (Fig. 4) were measured to determine magnetic parameters such as the saturation magnetization (Ms), remenant magnetization (Mr) and coercivity (Hc). The measurement results are presented in Table 1. The experimental magnetic moment (ZB) is determined from the
x=0.0 x=0.1 x=0.2 x=0.3 x=0.4
-1000
0 1000 Magnetization (emu/g)
2000
Fig. 4. Magnetic hysteresis loops for Ni0.5xCu0.2Zn0.3MgxFe2O4 system.
saturation magnetization data using the following formula [12]:
ZB ¼ MW MS =5585
(1)
where MW is the molecular weight of the sample and MS is the saturation magnetization in emu/g. Magnetization in ferrites is known to be strongly influenced by the site preference of the ions in the spinel lattice. This influence can be explained on the basis of the exchange interaction between the two crystallographic sites of ferrite. Zn2+ ions are preferentially occupying A-sites while Ni2+ and Mg2+ions have a strong preference to occupy the B-sites. Fe3+ and Cu2+ ions can exist at both sites though they have preference for the B-sites [13]. It is known that the magnetic moment of Ni2+ in spinel ferrite is 2.3 mB [14]; however, the magnetic moment of Mg2+ is zero. Since both of these ions occupy the octahedral sites, thus the subsequent substitution of Ni2+ ions by non-magnetic Mg2+ ions is expected to decrease the saturation magnetization and the net magnetic moment. However, the experimentally measured Ms value shows an increase with increasing Mg content up to a concentration of x ¼ 0.2 after which it decreases. Pradeep et al. [12] suggest a new cation distribution for MgFe2O4 in which Mg2+ ions were found to prefer both tetrahedral and octahedral sites occupation. They attributed this to the synthesis method and the impact of nanoregime. Thus the unexpected increase in the saturation magnetization with increasing Mg content can be attributed to the tendency of Mg2+ ions to occupy A-sites with a corresponding migration of the Fe3+ ions from A to B sites. This arrangement results in an increase in the magnetic moment of B sub-lattice as
ARTICLE IN PRESS M.A. Gabal / Journal of Magnetism and Magnetic Materials 321 (2009) 3144–3148
the Fe3+ ions have a higher magnetic moment (5 mB) than the Ni2+ ions which they replace. Besides the intrinsic factors attributed to preferential site occupancy of the ions, Ms is also influenced by extrinsic factors such as microstructure and the bulk density of the ferrites [15]. Pores act as pinning centers for the electron spins, thereby lowering the magnetization. Increasing the bulk density will result in a decrease in the number of the pores and increasing
12
X = 0.0
1010 G
10
1340 G 1660 G
8
1990 G
6
3147
magnetization. Also, as the grain size increases, formation of domain walls becomes possible and magnetization increases due to domain wall movement under the action of the magnetic field. Roy and Bera [7] reported that the permeability, which is a function of saturation magnetization, for Ni0.25xMgxCu0.2Zn0.55 Fe2O4 was found to increase with Mg substitution up to x ¼ 0.18. They attributed this behavior to the increase in the bulk density and the average crystallite size. In the present work, the gradual increase in the average crystallite size with the addition of magnesium up to x ¼ 0.2 (Table 1) agrees well with the increase in the saturation magnetization. The decrease in the coercivity (Hc) with increasing magnesium concentration may be attributed to the lower magneto-crystalline anisotropy of Mg2+ ions as compared to Ni2+ that leads to the lower coercivity according to the Stoner–Wolfforth model for coercivity of nanoparticles [16].
4 3.3.2. Magnetic susceptibility Fig. 5 shows the dependence of the molar magnetic susceptibility (wM) on absolute temperature, as a function of the magnetic field intensity, for the investigated samples. From the figure it is clear that all the samples show nearly the same trend but with different values of both wM and Tc depending on the Mg content. The decrease in wM with increasing field intensity can be considered as a normal magnetic behavior and can be attributed to the saturation of the ferromagnetic domains at such high field. The magnetic parameters such as Curie temperature (TC), Curie constant (C) and magnetic moment (m) at field intensity of 1990 G, for samples with different magnesium content, are reported in Table 1. For all the samples, the absence of any thermal stability of wM with increasing temperature indicates that the thermal energy is quite sufficient to disturb the ordered spins even at low temperatures. The samples show ferrimagnetic characteristics before reaching the Curie temperature (TC) after which a paramagnetic behavior dominates. The paramagnetic region was found to increase at the expense of the ferrimagnetic region by increasing the magnesium content. This indicates that the ferrimagnetic grains are widely separated and enclosed by the non-magnetic magnesium ions. The direct result of this behavior is the decreasing of the Curie temperature with increasing Mg substitution. The effective magnetic moments of the samples, calculated on the basis of the Curie–Weiss law using the values of the magnetic susceptibilities and the equation pffiffiffi meff ¼ 2:83 C (2)
2 0 12
X = 0.1
10 8 6 4 2 0 X = 0.2 8
χM
6 4 2 0 X = 0.3
8 6 4 2
was found to have the same trend, with increasing Mg content, as the magnetic moment calculated using hysteresis measurements (Table 1).
0 8
X = 0.4 4. Conclusion
6 4 2 0 300
400
500
600
700
800
T, K Fig. 5. Relation between molar magnetic susceptibility and the absolute temperature as a function of different magnetic field intensities for Ni0.5xCu0.2 Zn0.3MgxFe2O4 system.
Nanocrystalline NiCuZn ferrites were synthesized, for the first time, by using metal nitrates and freshly extracted egg white. TG measurement implied that the precursor can completely decompose at about 500 1C. XRD of precursors calcined at 500 1C indicate the formation of single-phase cubic ferrites with average particle size in the range 23.9–35.1 nm. TEM image corroborates well with XRD investigation and shows that each particle is permanently magnetized and gets agglomerated. Studying the effects of magnesium substitution for nickel, show that an improved magnetic property can be obtained. The highest saturation magnetization was found in the composition Ni0.3Cu0.2Zn0.3 Mg0.2Fe2O4, which would be better for more miniaturized
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multilayer chip inductor. The present investigations clearly point towards the merit of the egg white precursor method for preparing NiCuZn ferrites with enhanced properties at low processing temperatures, suitable for multilayer chip inductors.
Acknowledgements The Author is grateful to King Abdul Aziz University for providing financial support for this work (Project no. [3-048429]). Also, the author would like to express his thanks to Prof. Dr. M.A. Ahmed, Physics Department, Faculty of Science, Materials Science Laboratory (1), Cairo University, Egypt, for extending the facilities of magnetic susceptibility measurements. Thanks are extended also to Dr. Ayman Awad, Benha University, for his help and cooperation. References [1] X. Qi, J. Zhou, Z. Yue, et al., Key Eng. Mater. 224–226 (2002) 593. [2] P.K. Roy, J. Bera, J. Magn. Magn. Mater. 321 (2009) 247.
[3] A. Verma, T. Goel, R. Mendiratta, P. Kishan, J. Magn. Magn. Mater. 208 (2000) 19. [4] P.K. Roy, J. Bera, J. Mater. Process. Technol. 197 (2008) 279. [5] Y. Mine, Trends Food Sci. Technol. 6 (1995) 225. [6] S. Dhara, P. Bhargava, J. Am. Ceram. Soc. 86 (2003) 1645. [7] P. Roy, J. Bera, J. Magn. Magn. Mater. 298 (2006) 38. [8] I.H. Gul, A.Z. Abbasi, F. Amin, M. Anis-ur-Rehman, A. Maqsood, J. Magn. Magn. Mater. 311 (2007) 494. [9] R.D. Shannon, Acta Cryst. A 32 (1976) 751. [10] R.D. Waldron, Phys. Rev. 99 (1955) 1727. [11] E. Manova, B. Kunev, D. Paneva, I. Mitov, L. Petrov, C. Estourne`s, C. D’Orle´ans, J.L. Rehspringer, M. Kurmoo, Chem. Mater. 16 (2004) 5689. [12] A. Pradeep, P. Priyadharsini, G. Chandrasekaran, J. Magn. Magn. Mater. 320 (2008) 2774. [13] J. Smit, H.P.J. Wijn, Ferrites. Eindhovan, PhilipsTechnical Library, 1959, p. 149. [14] H. Su, H. Zhang, X. Tang, B. Liu, Z. Zhong, J. Alloys Compd. 475 (2009) 683. [15] M.C. Dimri, A. Verma, S.C. Kashyap, D.C. Dube, O.P. Thakur, C. Prakash, Mater. Sci. Eng. B 133 (2006) 42. [16] K. Maaz, W. Khalid, A. Mumtaz, S.K. Hasanain, J. Liu, J.L. Duan, Physica E 41 (2009) 593.
Contents lists available at ScienceDirect
Journal of Magnetism and Magnetic Materials journal homepage: www.elsevier.com/locate/jmmm
Effect of Mg substitution on the magnetic properties of NiCuZn ferrite nanoparticles prepared through a novel method using egg white M.A. Gabal Chemistry Department, Faculty of Science, King Abdul Aziz University, Jeddah, Saudi Arabia
a r t i c l e in f o
a b s t r a c t
Article history: Received 17 March 2009 Received in revised form 19 April 2009 Available online 29 May 2009
Nanocrystalline Mg-substituted NiCuZn ferrites were successfully synthesized, for the first time, by using metal nitrates and freshly extracted egg white. The thermal decomposition process of the nitrate–egg white precursors was investigated by thermogravimetric (TG) technique. X-ray diffraction (XRD) revealed that, single-phase cubic ferrites with average particle size of 23.9–35.1 nm were directly formed after ignition at 500 1C. No noticeable variation of lattice parameters with increasing magnesium content was observed, while X-ray densities were found to decrease. This can be explained on the basis of ionic radii and atomic masses of the substituted cation. Transmission electron microscope (TEM) shows that, particles are permanently magnetized and get agglomerated. The saturation magnetization (Ms) and coercivity (Hc) as a function of Mg content were investigated using vibrating sample magnetometer (VSM). It has been found that the Ms increases firstly up to x ¼ 0.2 and then decreases, while Hc continuously decreases. Magnetic susceptibility measurements give results which agree well with those obtained by VSM. The obvious decrease in the Curie temperature (TC) with increasing Mg indicates that the ferrimagnetic grains are widely separated and enclosed by nonmagnetic magnesium ions. & 2009 Elsevier B.V. All rights reserved.
Keywords: Mg substitution NiCuZn ferrite Egg white XRD VSM Susceptibility
1. Introduction With the rapid development of mobile communication and information technology, electronic components with small size, high efficiency and low cost are urgently demanded [1]. Multilayer chip inductor (MLCI) is a passive surface mount device widely used in electronic products, such as cellular phone, notebook computer and video cameras. Up to now, Ni–Cu–Zn ferrites have been the dominant materials for MLCI due to their better magnetic properties at high frequency and low sintering temperature [2]. Since silver (internal conductor) has a melting point of 961 1C, a much lower (o961 1C) sintering temperature of ferrite is preferred to suppress the diffusion of silver metal into the ferrite core. This metal diffusion into the ferrite body decreases the resistivity of the core. NiCuZn ferrite was usually prepared by the conventional ceramic method but the resultant products are not necessarily always stoichiometric or homogeneous [3]. Many new methods were tried to prepare the low firing temperature NiCuZn ferrite, of which the sol–gel self-propagating method was one [4]. The process has the advantages of being able to use inexpensive
Corresponding author. Permanent address: Chemistry Department, Faculty of Science, Benha University, Benha, Egypt. Tel.: +00966557071572. E-mail address: [email protected]
0304-8853/$ - see front matter & 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.jmmm.2009.05.047
precursors and a simple preparation method that results in nano-sized, homogeneous, highly reactive powder. In the present work, we tried to find simple and cost-effective routes to synthesize nanocrystalline NiCuZn ferrites by the utilization of cheap, nontoxic and environmentally benign precursors. Egg white proteins are well known for their gelling, foaming and emulsifying characteristics, in addition to their high nutrition quality [5]. Due to its solubility in water and its ability to associate with metal ions in solution, egg white has been used as a binder cum gel for shaping material, particularly bulk and porous ceramics [6]. The use of egg white simplifies the process and would provide another alternative process for the simple and economical synthesis of NiCuZn ferrites. Few studies on the electromagnetic properties of Mg-doped NiCuZn ferrites are present in the literature. Ni0.25xMgxCu0.2 Zn0.55Fe2O4 with x ¼ 0.0, 0.07, 0.13, 0.18 and 0.25 was synthesized through nitrate–citrate auto-combustion method [7]. The asburnt powders showed crystalline cubic spinel ferrite with about 19–22 nm crystallite sizes. The permeability and AC resistivity were found to increase and the magnetic loss decreased with Mg substitution. The composition with x ¼ 0.18 was found to be better than NiCuZn-based material for more miniaturization of MLCI. Mg-containing NiCuZn ferrites are preferred to avoid the presence of divalent iron and to avoid the tendency of discontinuous grain growth. Also the Mg substitution in NiCuZn ferrite was
ARTICLE IN PRESS M.A. Gabal / Journal of Magnetism and Magnetic Materials 321 (2009) 3144–3148
100 80 Mass loss (%)
found to improve its magnetic properties [7]. In addition, the preparation method is expected to play an important role on the different properties. Based on this, the present work is aiming at the investigation of the effect of Mg substitution for Ni on the magnetic properties of nano-sized Ni0.5xCu0.2Zn0.3MgxFe2O4 system, prepared at low temperature through a novel method using metal nitrate and egg white. So far to the knowledge of researchers, no literatures are available on this aspect.
3. Results and discussion 3.1. Thermal analysis studies Fig. 1. shows TG curves for pure egg white and the dried nitrate–egg white precursor (with magnesium content of 0.3). The curves show that, the decomposition rapidly propagated forward until all egg white was completely burnt out at about 500 1C. Accordingly, this temperature can be taken as the appropriate temperature for calcining the mixture. 3.2. Structural studies X-ray diffraction patterns of the as-prepared Ni0.5x Cu0.2Zn0.3MgxFe2O4 system show completely amorphous behavior of the materials. When the sintering temperature was increased to 500 1C, broad peaks corresponding to single-phase cubic spinel
60 40 Precursor
2. Experimental procedure
20 Pure egg-white
0
100
200
300 400 Temperature (°C)
500
600
Fig. 1. TG curves in air of pure egg white and precursor with Mg content of 0.3. Heating rate ¼ 5 1C min1.
(311)
(220)
Intensity (arb. units)
Ferrite powders of compositions; Ni0.5xCu0.2Zn0.3MgxFe2O4 (0.0rxr0.4) were prepared using ferric nitrate, zinc nitrate, nickel nitrate, magnesium nitrate and copper nitrate with high chemical purity. The stoichiometric amounts of metal nitrates were dissolved together in a minimum amount of doubly distilled water to get a clear solution. 60 ml of extracted egg white, dissolved in 40 ml of bi-distilled water through vigorous stirring, was added to the nitrate mixture at room temperature. After constant stirring for 30 min, the resultant sol–gel was evaporated at 80 1C until a dry precursor was obtained. Based on the thermal analysis measurements, the obtained precursors were calcined in an electric muffle at 500 1C for 1 h. Thermogravimetric (TG) analysis was carried out, using PerkinElmer thermal analyzer on precursors up to 850 1C at a heating rate of 5 1C min1. The sample mass in the Pt crucible was 10 mg. The phase identification of the as-burnt and calcined powders was performed by X-ray diffraction (XRD) on D8 Advance diffractometer (Bruker AXS, Germany) using Cu Ka1 radiation (l ¼ 1.5405 A˚). The average crystallite size of the synthesized powders was determined by X-ray line broadening technique using the well-known Scherrer formula [8]. Fourier transform infrared (FT-IR) spectroscopic analysis using KBr pellets was carried out using a Jasco model FT-IR 310 spectrophotometer. Transmission electron microscopy (TEM) was carried out on a JEOL 2010 transmission electron microscope with an accelerating voltage of 100 kV. A vibrating sample magnetometer (VSM) was used to measure the saturation magnetization (Ms) and intrinsic coercive force (Hc) of the annealed powders at room temperature. An applied magnetic field of 5 kOe to reach saturation values was used. The magnetic susceptibility of the investigated samples at different temperatures as a function of different magnetic field intensities was measured using Faraday’s method, in which the sample was inserted at the point of maximum force.
3145
(440)
(511) (222)
(400)
(422)
x = 0.4 x = 0.3 x = 0.2 x = 0.1
x = 0.0
20
30
40
50
60
70
2θ (deg) Fig. 2. Characteristic parts of XRD patterns of Ni0.5xCu0.2Zn0.3MgxFe2O4 system.
ferrite appeared (Fig. 2). The broadness of these peaks indicates the nanocrystalline nature of these ferrites. The lattice parameter, X-ray density and average crystallite size for the different samples are presented in Table 1. No noticeable variation of lattice parameters with increasing magnesium content was observed. This can be explained in terms of the ionic radii, where the difference in the ionic radii of Mg2+ (0.72 A˚) and Ni2+ (0.69 A˚) is small [9]. A similar behavior was reported by Roy and Bera for Mgsubstituted NiCuZn ferrite prepared through auto-combustion method [7]. The decrease in the X-ray density with increasing Mg content can be attributed to the substitution of heavier nickel atom by the lighter magnesium atom. This decrease in weight with constant size causes a decrease in the X-ray density. The average crystallite size of the ferrites is in the range 23.9–35.1 nm. It increases slightly with increasing Mg content up to x ¼ 0.2 and then decreases. FT-IR spectral data of Ni0.5xCu0.2Zn0.3MgxFe2O4 system calcined at 500 1C are shown in Table 1. In ferrite the metal cations are situated according to the geometric configuration of the oxygen ion nearest neighbors, in two different sub-lattices such as tetrahedral (A-sites) and octahedral (B-sites). The band n1 around 600 cm1 is attributed to stretching vibration of tetrahedral complexes and n2 around 400 cm1 to that of octahedral complexes [10]. The data in the table revealed that n1 and n2 are nearly constant with the addition of Mg. The slight decreases in the value of n2 from 412 cm–1 for the sample without Mg content to 401 cm–1 for that rich with magnesium can be attributed to the
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Table 1 Lattice parameters, X-ray densities, average crystallite size, FT-IR spectral data and magnetic data of Ni0.5xCu0.2Zn0.3MgxFe2O4 system. Parameters
x ¼ 0.0
x ¼ 0.1
x ¼ 0.2
x ¼ 0.3
x ¼ 0.4
Lattice parameter, a (A˚) X-ray density, Dx (g cm3) Average crystallite size, L (nm) Tetrahedral vibration, n1 (cm1) Octahedral vibration, n2 (cm1) Saturation magnetization, Ms (emu g1) Remenant magnetization, Mr (emu g1) Corecivity, Hc (emu g1) Magnetic moment, ZB (mB) Molar magnetic Susceptibility, wM (emu g1 mole1) Curie temperature, Tc (K) Curie constant, C (emu g1 mole1) Effective magnetic moment, meff (mB)
8.389 5.34 35.1 584 412 40.54 8.06 67.33 1.72 7.4 768 2.92 4.83
8.387 5.27 38.0 585 410 42.71 8.35 50.85 1.79 7.3 712 11.97 9.71
8.391 5.19 42.1 585 407 45.25 9.27 43.46 1.87 5.8 654 12.3 9.92
8.385 5.12 32.9 582 403 39.61 6.44 31.34 1.61 5.6 600 10.59 9.21
8.398 5.02 23.9 583 401 35.95 5.88 14.63 1.44 4.4 577 9.41 8.68
Magnetic field strength (Oe)
50
25
0
-25
-50 -2000
Fig. 3. TEM image of the sample with Mg content of 0.1.
tendency of magnesium ions, with slightly higher ionic radius than nickel, to occupy the octahedral site. 3.2. Morphological studies The TEM image of the sample with Mg content of 0.1 is shown in Fig. 3. The image illustrates the nanoscale nature of ferrite particles. Agglomerated particles as well as separated ones are present in the sample. Mainly the nanoparticles tend to agglomerate because they experience a permanent magnetic moment proportional to their volume [11]. Hence, each particle is permanently magnetized and gets agglomerated. The agglomeration can also be attributed, to a minor extent, to electrostatic or Van der Walls forces between particles. The image also shows that the particles are mostly in the 38–40 nm size range, which corroborates well with the XRD investigation. The shape of the majority of the nanoparticles appears spherical; however, some particles with straight edges are also present. 3.3. Magnetic properties studies 3.3.1. Hysteresis behavior The hysteresis loops of the investigated samples (Fig. 4) were measured to determine magnetic parameters such as the saturation magnetization (Ms), remenant magnetization (Mr) and coercivity (Hc). The measurement results are presented in Table 1. The experimental magnetic moment (ZB) is determined from the
x=0.0 x=0.1 x=0.2 x=0.3 x=0.4
-1000
0 1000 Magnetization (emu/g)
2000
Fig. 4. Magnetic hysteresis loops for Ni0.5xCu0.2Zn0.3MgxFe2O4 system.
saturation magnetization data using the following formula [12]:
ZB ¼ MW MS =5585
(1)
where MW is the molecular weight of the sample and MS is the saturation magnetization in emu/g. Magnetization in ferrites is known to be strongly influenced by the site preference of the ions in the spinel lattice. This influence can be explained on the basis of the exchange interaction between the two crystallographic sites of ferrite. Zn2+ ions are preferentially occupying A-sites while Ni2+ and Mg2+ions have a strong preference to occupy the B-sites. Fe3+ and Cu2+ ions can exist at both sites though they have preference for the B-sites [13]. It is known that the magnetic moment of Ni2+ in spinel ferrite is 2.3 mB [14]; however, the magnetic moment of Mg2+ is zero. Since both of these ions occupy the octahedral sites, thus the subsequent substitution of Ni2+ ions by non-magnetic Mg2+ ions is expected to decrease the saturation magnetization and the net magnetic moment. However, the experimentally measured Ms value shows an increase with increasing Mg content up to a concentration of x ¼ 0.2 after which it decreases. Pradeep et al. [12] suggest a new cation distribution for MgFe2O4 in which Mg2+ ions were found to prefer both tetrahedral and octahedral sites occupation. They attributed this to the synthesis method and the impact of nanoregime. Thus the unexpected increase in the saturation magnetization with increasing Mg content can be attributed to the tendency of Mg2+ ions to occupy A-sites with a corresponding migration of the Fe3+ ions from A to B sites. This arrangement results in an increase in the magnetic moment of B sub-lattice as
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the Fe3+ ions have a higher magnetic moment (5 mB) than the Ni2+ ions which they replace. Besides the intrinsic factors attributed to preferential site occupancy of the ions, Ms is also influenced by extrinsic factors such as microstructure and the bulk density of the ferrites [15]. Pores act as pinning centers for the electron spins, thereby lowering the magnetization. Increasing the bulk density will result in a decrease in the number of the pores and increasing
12
X = 0.0
1010 G
10
1340 G 1660 G
8
1990 G
6
3147
magnetization. Also, as the grain size increases, formation of domain walls becomes possible and magnetization increases due to domain wall movement under the action of the magnetic field. Roy and Bera [7] reported that the permeability, which is a function of saturation magnetization, for Ni0.25xMgxCu0.2Zn0.55 Fe2O4 was found to increase with Mg substitution up to x ¼ 0.18. They attributed this behavior to the increase in the bulk density and the average crystallite size. In the present work, the gradual increase in the average crystallite size with the addition of magnesium up to x ¼ 0.2 (Table 1) agrees well with the increase in the saturation magnetization. The decrease in the coercivity (Hc) with increasing magnesium concentration may be attributed to the lower magneto-crystalline anisotropy of Mg2+ ions as compared to Ni2+ that leads to the lower coercivity according to the Stoner–Wolfforth model for coercivity of nanoparticles [16].
4 3.3.2. Magnetic susceptibility Fig. 5 shows the dependence of the molar magnetic susceptibility (wM) on absolute temperature, as a function of the magnetic field intensity, for the investigated samples. From the figure it is clear that all the samples show nearly the same trend but with different values of both wM and Tc depending on the Mg content. The decrease in wM with increasing field intensity can be considered as a normal magnetic behavior and can be attributed to the saturation of the ferromagnetic domains at such high field. The magnetic parameters such as Curie temperature (TC), Curie constant (C) and magnetic moment (m) at field intensity of 1990 G, for samples with different magnesium content, are reported in Table 1. For all the samples, the absence of any thermal stability of wM with increasing temperature indicates that the thermal energy is quite sufficient to disturb the ordered spins even at low temperatures. The samples show ferrimagnetic characteristics before reaching the Curie temperature (TC) after which a paramagnetic behavior dominates. The paramagnetic region was found to increase at the expense of the ferrimagnetic region by increasing the magnesium content. This indicates that the ferrimagnetic grains are widely separated and enclosed by the non-magnetic magnesium ions. The direct result of this behavior is the decreasing of the Curie temperature with increasing Mg substitution. The effective magnetic moments of the samples, calculated on the basis of the Curie–Weiss law using the values of the magnetic susceptibilities and the equation pffiffiffi meff ¼ 2:83 C (2)
2 0 12
X = 0.1
10 8 6 4 2 0 X = 0.2 8
χM
6 4 2 0 X = 0.3
8 6 4 2
was found to have the same trend, with increasing Mg content, as the magnetic moment calculated using hysteresis measurements (Table 1).
0 8
X = 0.4 4. Conclusion
6 4 2 0 300
400
500
600
700
800
T, K Fig. 5. Relation between molar magnetic susceptibility and the absolute temperature as a function of different magnetic field intensities for Ni0.5xCu0.2 Zn0.3MgxFe2O4 system.
Nanocrystalline NiCuZn ferrites were synthesized, for the first time, by using metal nitrates and freshly extracted egg white. TG measurement implied that the precursor can completely decompose at about 500 1C. XRD of precursors calcined at 500 1C indicate the formation of single-phase cubic ferrites with average particle size in the range 23.9–35.1 nm. TEM image corroborates well with XRD investigation and shows that each particle is permanently magnetized and gets agglomerated. Studying the effects of magnesium substitution for nickel, show that an improved magnetic property can be obtained. The highest saturation magnetization was found in the composition Ni0.3Cu0.2Zn0.3 Mg0.2Fe2O4, which would be better for more miniaturized
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multilayer chip inductor. The present investigations clearly point towards the merit of the egg white precursor method for preparing NiCuZn ferrites with enhanced properties at low processing temperatures, suitable for multilayer chip inductors.
Acknowledgements The Author is grateful to King Abdul Aziz University for providing financial support for this work (Project no. [3-048429]). Also, the author would like to express his thanks to Prof. Dr. M.A. Ahmed, Physics Department, Faculty of Science, Materials Science Laboratory (1), Cairo University, Egypt, for extending the facilities of magnetic susceptibility measurements. Thanks are extended also to Dr. Ayman Awad, Benha University, for his help and cooperation. References [1] X. Qi, J. Zhou, Z. Yue, et al., Key Eng. Mater. 224–226 (2002) 593. [2] P.K. Roy, J. Bera, J. Magn. Magn. Mater. 321 (2009) 247.
[3] A. Verma, T. Goel, R. Mendiratta, P. Kishan, J. Magn. Magn. Mater. 208 (2000) 19. [4] P.K. Roy, J. Bera, J. Mater. Process. Technol. 197 (2008) 279. [5] Y. Mine, Trends Food Sci. Technol. 6 (1995) 225. [6] S. Dhara, P. Bhargava, J. Am. Ceram. Soc. 86 (2003) 1645. [7] P. Roy, J. Bera, J. Magn. Magn. Mater. 298 (2006) 38. [8] I.H. Gul, A.Z. Abbasi, F. Amin, M. Anis-ur-Rehman, A. Maqsood, J. Magn. Magn. Mater. 311 (2007) 494. [9] R.D. Shannon, Acta Cryst. A 32 (1976) 751. [10] R.D. Waldron, Phys. Rev. 99 (1955) 1727. [11] E. Manova, B. Kunev, D. Paneva, I. Mitov, L. Petrov, C. Estourne`s, C. D’Orle´ans, J.L. Rehspringer, M. Kurmoo, Chem. Mater. 16 (2004) 5689. [12] A. Pradeep, P. Priyadharsini, G. Chandrasekaran, J. Magn. Magn. Mater. 320 (2008) 2774. [13] J. Smit, H.P.J. Wijn, Ferrites. Eindhovan, PhilipsTechnical Library, 1959, p. 149. [14] H. Su, H. Zhang, X. Tang, B. Liu, Z. Zhong, J. Alloys Compd. 475 (2009) 683. [15] M.C. Dimri, A. Verma, S.C. Kashyap, D.C. Dube, O.P. Thakur, C. Prakash, Mater. Sci. Eng. B 133 (2006) 42. [16] K. Maaz, W. Khalid, A. Mumtaz, S.K. Hasanain, J. Liu, J.L. Duan, Physica E 41 (2009) 593.