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International Journal of Modern Physics B Vol. 21, No. 15 (2007) 2669–2677 c World Scientific Publishing Company
MAGNETIC PROPERTIES OF CO-PRECIPITATED MnZn FERRITE-SiO2 COMPOSITES
M. U. ISLAM,∗ M. AZHAR KHAN, ZULFIQAR ALI, SHAHIDA B. NIAZI,† M. ISHAQUE and T. ABBAS Department of Physics, Bahauddin Zakariya University, Multan, Pakistan of Chemistry, Bahauddin Zakariya University, Multan, Pakistan ∗
[email protected]
† Department
Received 2 August 2006 A series of composite ferrites with chemical formula (1 − x)[Mn0.5 Zn0.5 Fe2 O4 ] · x[SiO2 ] (x = 0.0, 0.20, 0.30, 0.40, 0.50) were prepared by the co-precipitation technique. The samples were finally sintered at 1150◦ C followed by air quenching. The x-ray diffraction analysis confirms the phases precipitated out in the samples. AC magnetic susceptibility of these samples has been measured using the low field mutual inductance technique over the temperature range 298 K to 550 K at a frequency of 250 Hz. The magnetic parameters like Curie constant, C, Curie temperature, Tc , Lande splitting factor, g, effective magnetic moment, Peff , exchange integral, J/kB, and characteristic temperature, θ(K) were calculated. The reciprocal of susceptibility versus temperature curves of each sample follows the Curie Weiss behaviour above the Curie temperature. Below the Curie temperature, all the samples show the ferrimagnetic behaviour. It was concluded that the magnetic properties were enhanced by the addition of silicon as is evident by the variation of magnetic interactions J, with Si-concentration and followed subsequently by the Peff , θ(K) and Tc etc. Keywords: Composite ferrites; co-precipitation; susceptibility; magnetic interactions.
1. Introduction Composite ferrites have a large number of technological applications.1 Nowadays, ferrites composite materials, obtained by embedding soft magnetic particles (ferrites) in a non-magnetic matrix, have interesting physical, chemical and electromagnetic properties due to their peculiar structures. Different techniques are being used for the fabrication of such materials. NiZn ferrite – SiO2 composites synthesized by a sol-gel method have been reported.2 The initial permeability was reported to increase with ferrite content. This was attributed to homogeneous mixing and the small grain size of reactants. Composite ferrites are being used in microelectronics and micromachining for their applications as integrated inductive components, electromagnetic interference shielding and microsensors. Ferrite/polyimide ∗ Corresponding
author. 2669
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thin film composites have been synthesized.3 The synthesized composites show good hard magnetic properties, square magnetization curves, high coercivity around 4.022 × 103Oe and residual magnetization ∼ 0.3 × 104Oe and make an energy product ∼ 1.496 × 103 GOe. These parameters were ascertained to be comparable with bulk ferrites.3 Due to good magnetic and mechanical properties and machinability, these composite materials were useful in micro sensors, power conversion devices etc. Process ability, hardness and magnetic properties of rubber ferrite composites containing MnZn-ferrites have been reported.4 Composites made by blending natural rubber with the MnZn-ferrites have been reported to show almost the same Curie temperature as natural rubber itself. The Curie temperature, minimum torque and maximum torque were marginally affected by loading and this indicates no change in process ability by the addition of MnZn ferrite.4 In the present paper, MnZn ferrite-SiO2 composites were prepared by a chemical route in order to investigate the enhancement of the magnetic properties. For this purpose, magnetic susceptibility was measured by the mutual inductance technique and discussed thoroughly. 2. Experimental Procedure The metal chlorides and silicon dioxide (MnCl2 4H2 O, ZnCl2 , FeCl3 ·6H2 O and SiO2 ) were weighed using an electronic balance having an accuracy up to 1 × 10 −4 gm. They were mixed in an appropriate proportion using the chemical formula (1 − x)[Mn0.5 Zn0.5 Fe2 O4 ] · x[SiO2 ] (x = 0.0, 0.20, 0.30, 0.40, 0.50). The formula weights of salts used are given as; MnCl2 ·4H2 O = 197.91 gm/mol, ZnCl2 = 136.29 gm/mol, FeCl3 · 6H2 O = 270.30 gm/mol and SiO2 = 60.078 gm/mol. Metal chlorides with stoichiometric composition of (1 − x)[Mn0.5 Zn0.5 Fe2 O4 ] · x[SiO2 ] (x = 0.0, 0.20, 0.30, 0.40, 0.50) were dissolved one by one in 100 ml of distilled water contained in a 500 ml beaker and stirred constantly with the help of a magnetic stirrer until a clear homogeneous solution was obtained. The precipitating agent used was NaOH. The calculated weight of NaOH used for each sample was 4.0 gm. The precipitating agent was added slowly with constant mixing until precipitation occurred. The supernatant solution was tested in order to check the completion of precipitates. When the precipitation was completed, the contents were left aside for settling down and the precipitates were then filtered with the help of a suction flask operating on a water pump. The precipitates were thoroughly washed with distilled water several times until the removal of Cl1− ions is confirmed. This was checked by adding a drop of AgNO3 aqueous solution in the last washings. This co-precipitated product contains moisture along with carbonates and hydroxide ions. This co-precipitated product was dried (to remove moisture) in an electric oven at a temperature of 100 ± 5 ◦ C overnight. The dried material was ground for 2 hrs in an agate pestle mortar to obtain a homogenous powder. Before and after this process, the pestle mortar was rinsed with acetone. The finally ground powder was then pressed into pellets using a hydraulic pressing machine (Paul-Otto-Weber) under the load of 30 kN. All the
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samples were ground and pelletized under the same conditions. The pellets were pre-sintered at 600◦C for 3 hrs, at 800◦ C for 18 hrs and at 1000◦C for 2 hrs. Final sintering was done at 1150◦C for 3 hrs followed by air quenching. 3. Results and Discussion After final sintering at 1150◦ C, the x-ray diffraction patterns of each sample were taken and indexed. XRD patterns of these samples are shown in Fig. 1. The XRD analysis revealed biphase samples except x = 0.0. The hkl, 2θ and d-values of each sample are listed in Tables 1–5. These d-values were compared using the data cards.5
(degrees) Fig. 1. Representative X-ray diffraction patterns of (1−x)[Mn0.5 Zn0.5 Fe2 O4 ]·x[SiO2 ] composite ferrites (x = 0.0 − 0.5). Table 1. X-ray diffraction data for (1 − x) [Mn0.5 Zn0.5 Fe2 O4 ] · x[SiO2 ] composite ferrites (x = 0.0). 2θ (Degrees)
d(˚ A)
hkl
30 35.4 56.8 62.3 68.0
2.98 2.54 1.62 1.49 1.39
220 311 511 440 600
Phase ferrite ferrite ferrite ferrite ferrite
(fcc) (fcc) (fcc) (fcc) (fcc)
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M. U. Islam et al. Table 2. X-ray diffraction data for (1 − x) [Mn0.5 Zn0.5 Fe2 O4 ] · x[SiO2 ] composite ferrites (x = 0.2). 2θ (Degrees)
d(˚ A)
hkl
30 35.5 41.8 56.8 60.9 62.3 68.0 73.0
2.98 2.52 2.16 1.62 1.52 1.49 1.38 1.29
220 311 312 511 440 222 600 622
Phase ferrite (fcc) ferrite (fcc) (Mn, Fe)SiO3 ferrite (fcc) ferrite (fcc) (Fe, Mn)O2 ferrite (fcc) MnFe2 O4
Table 3. X-ray diffraction data for (1 − x) [Mn0.5 Zn0.5 Fe2 O4 ] · x[SiO2 ] composite ferrites (x = 0.3). 2θ (Degrees)
d(˚ A)
hkl
20.9 25.8 31.0 35.3 42.5 49.2 59.4 62.0 68
4.24 3.45 2.88 2.54 2.12 1.85 1.55 1.49 1.38
111 020 220 311 028 331 511 222 401
Phase ferrite (fcc) (Mn,Fe)SiO3 ferrite (fcc) ferrite (fcc) (Mn,Fe)SiO3 ferrite (fcc) ferrite (fcc) (Fe,Mn)O2 (Fe,Mn)O2
Table 4. X-ray diffraction data for (1 − x) [Mn0.5 Zn0.5 Fe2 O4 ] · x[SiO2 ] composite ferrites (x = 0.4). 2θ (Degrees)
d(˚ A)
hkl
30 35.4 42.9 50.8 56.8 62.0 68.0
2.98 2.53 2.10 1.79 1.62 1.49 1.38
220 311 400 046 511 440 401
Phase ferrite (fcc) ferrite (fcc) ferrite (fcc) (Mn,Fe)SiO3 ferrite (fcc) ferrite (fcc) (Fe,Mn)O2
The magnetic susceptibility of (1 − x)[Mn0.5 Zn0.5 Fe2 O4 ] · x[SiO2 ] composite ferrites was measured over the temperature range of 298–550 K using the low field ac mutual inductance technique. The measuring frequency used was 250 Hz with a field of 76.90 mOe. The results of susceptibility measurements are shown in Fig. 2. AC susceptibility of MnZnferrite-SiO2 composites appears to follow the Curie Weiss behaviour at high temperatures, with marked deviation from this behaviour for all
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Table 5. X-ray diffraction data for (1 − x) [Mn0.5 Zn0.5 Fe2 O4 ] · x[SiO2 ] composite ferrites (x = 0.5). 2θ (Degree)
d(˚ A)
hkl
26.0 29.5 35.3 39.0 50.2 56.8 62.0 68.0
3.42 3.02 2.52 2.30 1.82 1.62 1.49 1.38
020 220 311 800 046 511 440 401
Phase (Mn,Fe)SiO3 ferrite (fcc) ferrite (fcc) FeSiO3 (Mn,Fe)SiO3 ferrite (fcc) ferrite (fcc) (Fe,Mn)O2
2.5
1/F (g/emu)
2
X=0.0 X=0.2 X=0.3 X=0.4 X=0.5
1.5
1
0.5
0 300
350
400
450
500
550
600
T (K )
Fig. 2. Reciprocal of susceptibility (1/χ) versus temperature (K) for (1 − x)[Mn 0.5 Zn0.5 Fe2 O4 ] · x[SiO2 ] composites (x = 0.0 − 0.5).
the samples at temperatures below the Curie temperature. From this linear portion of the 1/χ versus T plots, the Curie constants (C) were calculated as well as the paramagnetic Curie temperature (θ) and effective magnetic moments (Peff ). Using the Curie Weiss law;6 χ = C/T − θ .
(1)
It can be seen that the Curie constant C (emuK/gm) is just the reciprocal of the slope of the 1/χ versus T plot. This constant has the form as follows;7 C = Ng2 µB S(S + 1)/3 kB ,
(2)
where N is the total number of magnetic moments within the sample and S, µB and kB are the spin, magnetic moment and Boltzmann‘s constant respectively. In the present samples, manganese (Mn) possesses a magnetic moment. If C is converted
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Table 6. Magnetic parameters: Curie constant, C, Curie temperature, T c , Lande splitting factor, g, effective magnetic moment, Peff , exchange integral, J, and characteristic temperature, θ(K) for (1 − x)[Mn0.5 Zn0.5 Fe2 O4 ] · x[SiO2 ] composites. Mole fraction (x) 0.00 0.20 0.30 0.40 0.50
C(emuK/gm)
C(emuK/ mole) Mn
g
Tc (K)
Peff (µB )
θ(K)
Exchange Integral (J/kB )
0.142 0.357 0.582 0.410 0.606
1.1902 3.2206 5.5418 4.1624 6.686
1.04 1.71 2.25 1.95 2.47
408.56 425.70 429.98 432.84 434.27
3.07 5.05 6.65 5.76 7.30
−71.42 −64.26 −61.40 −57.12 −45.69
−24.48 −22.03 −21.05 −19.58 −15.66
into units of (emuK/mole of Mn) then one can find the effective magnetic moments, Peff using the formula, Peff = g[s(s + 1)]1/2
(3)
and the corresponding Lande g-factor. The values of the exchange integrals (J/k B ) were calculated using the relation; J/kB = −3θ(K)/S(S + 1) .
(4)
The least square fit to the straight lines of the 1/χ versus T plots were made to determine (θ) and the Curie constant (C) for each sample. The values of these parameters for each sample are listed in Table 6. The magnetic behaviour of (1 − x)[Mn0.5 Zn0.5 Fe2 O4 ] · x[SiO2 ] composite ferrites can be discussed by examining the 1/χ versus T plots of each sample as shown in Fig. 2. Plots of 1/χ versus T for each sample above the Curie temperature (Tc ) shows a linear behaviour. The extrapolation of the linear portion of these plots intercepts the negative temperature axis, proving that the dominant interactions within these ferrites is ferrimagnetic (special case of antiferromagnetic). The values of P eff range from 3.07 to 7.30 Bohr’s magnetons as shown in Table 6. The calculated effective magnetic moments for these samples are plotted versus the Si-concentration in Fig. 3. It reveals that the effective magnetic moment increases with the increase in Si content. It shows that the magnetization increases as the Si-concentration increases. The plot of Curie temperature (Tc ) versus Si-concentration is shown in Fig. 4. The Curie temperature of MnZnferrite-SiO2 composites varies with different methods of preparation and with the substitution of non-magnetic atoms. It is reported that the Curie temperature of MnZn-ferrite-SiO2 composites shows a linear increase in Curie temperature as the Si-content is increased.8 Since the present samples are biphase due to the addition of silicon and the effective magnetic moment has been increased and the interaction between the atoms on various sites increases, causing the Tc to increase.9 The plot of characteristic temperature θ(K) versus Si-concentration is shown in Fig. 5. The θ values are negative
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8 7
Peff
6 5 4 3 2 0
0.1
0.2
0.3
0.4
0.5
0.6
Si concentration(x) Fig. 3. Effective magnetic moment (Peff ) versus Si Concentration for (1 − x)[Mn0.5 Zn0.5 Fe2 O4 ] · x[SiO2 ] composites (x = 0.0 − 0.5).
440 435
Tc (K)
430 425 420 415 410 405 0
0.1
0.2
0.3
0.4
0.5
S i-C oncentra tion (x) Fig. 4. Curie Temperature (Tc ) versus Si Concentration for (1 − x)[Mn0.5 Zn0.5 Fe2 O4 ] · x[SiO2 ] composites (x = 0.0 − 0.5).
which shows that the samples are ferrimagnetic. It can be seen that the characteristic temperature(θ) increases as the Si-concentration is increased. The magnetic interactions (J/kB ) versus Si-concentration plots for MnZnferrite-SiO2 composites are shown in Fig. 6, which shows the increasing behaviour of magnetic interactions as the Si-concentration is increased. Generally, in ferrites there are three exchange integrals Jab , Jaa and Jbb which are all usually negative with Jab Jaa and Jbb .
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-40 -45 -50
T K)
-55 -60 -65 -70 -75 0
0.1
0.2
0.3
0.4
0.5
S i c o n c e n tr a tio n (x )
Fig. 5. Characteristic temperature(θ) versus Si-Concentration for (1 − x)[Mn 0.5 Zn0.5 Fe2 O4 ] · x[SiO2 ] composites (x = 0.0 − 0.5).
-15 -16 -17
-1
J/k(K )
-18 -19 -20 -21 -22 -23 -24 -25 0
0.1
0.2
0.3
0.4
0.5
0.6
Si concentration(x) Fig. 6. Magnetic Interactions(J/k) versus Si-Concentration for (1−x)[Mn 0.5 Zn0.5 Fe2 O4 ]·x[SiO2 ] composites (x = 0.0 − 0.5).
Therefore, the two magnetic sub-lattices are anti-parallel and Jaa and Jbb are frustrated. In the present case of MnZn-ferrite-SiO2 composites, the Jab integral is strengthened by the addition of a small amount of SiO2 of about x = 0.05, causing the magnetic interactions and hence the magnetic properties to be enhanced.10 – 11 If Jab is not much larger than Jaa and Jbb , then the two magnetic sub-lattices are anti-parallel and Jaa and Jbb are frustrated to a smaller extent, indicating long
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range magnetic order in MnZn ferrite-SiO2 composites. That is why the magnetization is increased by the addition of Si in MnZn-ferrite. 4. Conclusion The present composite ferrites exhibit enhanced magnetic properties due to fine grains and by the addition of Si in the lattice. It was observed that the effective magnetic moments (Peff ), Curie temperature (Tc ), Characteristic temperature (θ) and exchange integral (J/kB ) show increasing behaviour, revealing the enhancement of magnetic properties. References 1. B. Viswanathan and V. R. K. Murthy, Ferrite Materials (Springer–Verlag, Narosa Publishing House, New Delhi, 1990). 2. X. H. He, Q. Q. Zhang and Z. Y. Ling, Materials Letters 57, 3031 (2003). 3. L. K. Lagorce and M. G. Allen, Journal of Microelectromechanical Systems 6(4), 307 (1997). 4. E. M. Mohammad, K. A. Malini, P. A. Joy, S. D. Kulkarni, S. K. Date, P. Kurian and M. R. Anantharaman, Plastics, Rubber and Composites 31(3), 106 (2002). 5. P. Bayliss, D. C. Erd, M. E. Mrose, A. P. Sabina and D. K. Smith, Mineral Powder Diffraction File, 1st edn. (JCPDS-International Centre for Diffraction Data, USA, 1986). 6. R. S. Tebble and D. J. Craik, Magnetic Materials (John Wiley and Sons Publishers, New York, 1969). 7. M. U. Rana, Misbah-Ul-Islam and T. Abbas, Solid State Communications 126, 129 (2003). 8. S. E. Harrison, C. J. Kriessman and S. R. Pollack, Phy. Rev. 110(4), 844 (1958). 9. Misbah-Ul-Islam, K. A. Hashmi, M. U. Rana and T. Abbas, Solid State Communications 121, 51 (2002). 10. J. L. Dorman and M. Nogues, J. Phys. Condens. Matter 2, 1223 (1990). 11. S. R. Mekala and J. Ding, Journal of Alloys and Compounds 296(1–2), 152 (2000).
