Nội dung

Journal of Advanced Research (2014) 5, 601–605 Cairo University Journal of Advanced Research ORIGINAL ARTICLE Improvement of the magnetic properties for Mn–Ni–Zn ferrites by rare earth Nd3+ ion substitution M.M. Eltabey a,b , W.R. Agami c,* , H.T. Mohsen b,d a Basic Engineering Science Department, Faculty of Engineering, Menoufiya University, Shebin El-Kom, Egypt Science Department – Physics, Preparatory Year Deanship, Jazan University, Saudi Arabia c Department of Physics, Faculty of Science, Ain Shams University, 11566 Abbasia, Cairo, Egypt d Accelerators and Ion Sources Department, Nuclear Research Center, P.O. Box 13759, Cairo, Egypt b A R T I C L E I N F O Article history: Received 24 June 2013 Received in revised form 27 August 2013 Accepted 29 August 2013 Available online 3 September 2013 Keywords: Ferrites EDX Magnetization Initial permeability A B S T R A C T Single spinel phases of Mn0.5Ni0.1Zn0.4NdxFe2xO4 ferrite samples (x = 0.0, 0.01, 0.02, 0.05, 0.075, and 0.1) have been prepared by ceramic method and the composition dependence of the physical and magnetic properties has been investigated. SEM micrographs and EDX analysis revealed that there is no considerable effect for the Nd3+ ion substitution on the average grain size or porosity, whereas its concentration in the grain boundaries is higher than that in the grains. Saturation magnetization (MS) increased with the Nd3+ ion concentration (x) and reached a maximum value at x = 0.05. In addition, both the initial permeability and the magnetic homogeneity increased by increasing the Nd3+ ion content. The value of Curie temperature increased due to the substitution by Nd3+ ions to record about 170 K, for the sample with x = 0.05, higher than that of the un-substituted one. ª 2013 Production and hosting by Elsevier B.V. on behalf of Cairo University. Introduction Both Mn–Zn and Ni–Zn ferrites have a great importance from the application point of view, where they are used in many ferrite devices such as inductor cores, converters, magnetic heads, and electromagnetic wave absorbers. Although Mn–Zn ferrites have distinctive magnetic properties as high initial permeabil* Corresponding author. Tel.: +20 1144105038; fax: +20 24665630. E-mail address: walid_abdelrasheed@sci.asu.edu.eg (W.R. Agami). Peer review under responsibility of Cairo University. Production and hosting by Elsevier ity and magnetization, they have low electrical resistivity and high power losses. So, they are not suitable for magnetic applications especially at high frequencies. On the other hand, Ni– Zn ferrites are characterized by their high resistivity, low dielectric loss and high Curie temperature, but they have relatively low initial permeability at high frequencies. Combinations between these two ferrites were carried out by many studies trying to obtain favorable magnetic properties with low losses especially at high frequencies in bulk and powder forms [1–10]. In a previous work, the magnetic and electrical properties of such a combination were investigated [11,12]. The sample with the chemical formula Mn0.5Ni0.1Zn0.4Fe2O4 was found to possess the optimum properties for promising applications. Moreover, it was noticed clearly that the properties of Mn–Ni–Zn ferrites are predominantly governed by the 2090-1232 ª 2013 Production and hosting by Elsevier B.V. on behalf of Cairo University. http://dx.doi.org/10.1016/j.jare.2013.08.005 602 M.M. Eltabey et al. Ferrite samples with the chemical formula Mn0.5Ni0.1Zn0.4 NdxFe2xO4 (x = 0.0, 0.01, 0.02, 0.05, 0.075 and 0.1) were prepared by the usual standard ceramic method. Details about the preparation conditions were previously reported [11]. X-ray diffraction patterns were performed using a diffractometer of type X’Pert Graphics and identified with Cu Ka radiation. The Scanning Electron Microscope (SEM) of type JSM-5600-LV was used for imaging the samples. Digital Image Processing (DIP) software was used for image analysis of samples. Different image analysis filters were used for determination of grains. The observed samples were polished and etched before imaging by SEM. According to the American Society for Testing and Materials (ASTM) intercept method, and after imaging the sample by SEM, the average particle size of grains was determined using particle counting method [13]. Energy Dispersive X-ray spectrometer (EDX) was used to analyze both the grain and the grain boundaries. The magnetization was measured for powder samples, at room temperature, using Vibrating Sample Magnetometer (VSM, EG&G PARC model no. 1551 USA). The porosity percentage (P%) and the initial permeability (li) were measured according to the techniques and methods mentioned elsewhere [11,12]. 8.465 8 8.460 6 8.455 a P(%) 8.450 4 8.445 Porosity P (%) Material and methods 10 8.470 Lattice parameter a (Angstrom) type of substituted ions [2,12]. Accordingly, this work deals with the improvement of the magnetic properties of this last optimum sample when Nd3+ ions substitute only Fe3+ ions. This may present a candidate for magnetic applications in high frequency field. 2 8.440 8.435 0 0.00 0.02 0.04 0.06 0.08 0.10 Nd- concentration (x) Fig. 2 Variation of the lattice parameter a (Å) and Porosity P (%) with Nd-concentration (x). X-ray diffraction Porosity, SEM and EDX X-ray diffraction patterns, (Fig. 1), showed that all the investigated samples have single cubic spinel phase. Values of the lattice parameter (a) were calculated according to the procedure mentioned before [14]. Fig. 2 shows the variation of the lattice parameter as a function of Nd-concentration (x). It can be seen that the lattice parameter decreases dramatically with the The composition dependence of porosity is illustrated in Fig. 2. One can note the absence of any considerable change in the value of porosity by increasing the Nd-content. This could be linked to the constancy in the average value of the grain size shown by SEM micrographs. Fig. 3 shows the SEM micrographs for the samples with x = 0.0, 0.05, and 0.1. It is obvious that the substitution by Nd3+ ions in our system has no noticeable effect on the grain size. The average value of the grain size determined by ASTM intercept method is about 4.2 lm. The energy dispersive X-ray spectra (EDX) for the sample with x = 0.05 at the grain and grain boundaries are represented in Fig. 4. The analysis of EDX data is collected in two tables as insets in the same figure. Each table contains two columns; one is for the element percentage and the other is for the atomic percentage. The element percentage values represent the raw data of the emitted X-ray intensities which arrive to the detector of the EDX spectrometer. On the other hand, the atomic percentage values come from three iterations for the ZAF quantitative method. This method takes three parameters in consideration: the atomic number of each element (Z), the absorption of the emitted X-ray by the sample elements themselves (A), and the amount of X-ray fluorescence which results from the sample elements due to the absorption of emitted X-ray (F). One can note that the element percentage data show that the concentrations of elements are in non-stoichiometric proportion form, Counts (a. u) (533) (440) (511) (422) (400) (222) x= 0.1 (220) (311) Results and discussion Nd-concentration up to x = 0.05 then it becomes nearly constant for 0.05 < x 6 0.1. For x 6 0.05, the decrease in the lattice parameter could be attributed to that some rare earth ions reside at the grain boundaries [15]. Hence, they hinder the grain growth and may exert a pressure on the grains and lead the lattice parameter to decrease. The presence of higher concentrations of Nd3+ ions in the grain boundaries than that in the grains was confirmed by EDX analysis and it will be discussed in the next section. On the other side, for 0.05 < x 6 0.1, some of the Nd3+ ions (radius = 0.983 Å) [16] that substitute Fe3+ ions (radius = 0.645 Å) [16] in the unit cell may cause the increase in the lattice parameter which in turn compensates the decrease due to the grain boundaries pressure. 0.075 0.05 0.02 0.01 0.00 20 30 40 50 60 70 2theta (degree) Fig. 1 X-ray diffraction patterns for Mn0.5Ni0.1Zn0.4NdxFe2xO4. Improving the magnetic properties of Mn–Ni–Zn ferrites 603 x= 0 Counts Elem. Cl Mn Fe Ni Zn Nd O Grain Percentage Elem. Atomic 13.75 8.52 43.79 26.69 1.71 0.99 13.17 6.86 0.92 0.22 26.66 56.73 10 µm x = 0.05 Energy (keV) Elem. Counts 10 µm Cl Mn Fe Ni Zn Nd O GrainBoundary Percentage Elem. Atomic 1.56 1.5 11.46 7.09 46.39 28.23 1.73 1 10.02 5.21 0.53 2.26 26.57 56.44 x = 0.1 Energy (keV) 10 µm Fig. 3 SEM micrographs for Mn0.5Ni0.1Zn0.4NdxFe2xO4 ferrite samples with x = 0.0, 0.05, and 0.1. Fig. 4 EDX spectra for sample with x = 0.05 at the grain and grain boundaries. Tables of the EDX data analysis at the grain and grain boundaries are in two insets. Magnetic studies Magnetization whereas the atomic percentage one is nearly fully stoichiometric. The difference between the data of the two columns could be discussed according to the previously reported parameters of the ZAF quantitative method. Although the concentration of O element in the prepared sample is higher than that of Fe, the element percentage value of oxygen is lower than that of iron. This could be attributed to the energy of the emitted oxygen X-ray which is much lower than that of iron. The lower the energy the lower the penetration, so the amount of X-ray arrives to the detector from O anions is lower than that arrives from Fe cations. Moreover, some traces of Cl element were detected in grain boundaries. These traces remained after washing the sample through the etching process. One of the clearest remarks in these tables is that the concentration of Nd element in the grain boundaries, in both columns, is more than twice that in the grains. In other words, the Nd3+ rare earth ions in our ferrite system tend to concentrate in the grain boundaries, which is in agreement with the previously reported results [17,18]. The variation of the magnetization M (emu/g) versus the applied magnetic field H (Oe), at room temperature, is illustrated in Fig. 5. The dependence of the saturation magnetization (MS) on the Nd-concentration (x) is shown in an inset in Fig. 5. It can be seen that MS increases with x and attains a maximum value at x = 0.05 with a percentage increase of 26.5% relative to that of the un-substituted sample. Further increase in the Nd-concentration leads MS to decrease but with values still larger than that for the sample with x = 0. Such a result could be discussed assuming the following cation distribution: þ2 3þ 2þ 3þ 2þ 3þ ðZn2þ 0:4 Mn0:4 Fe0:2 Þ½Ni0:1 Mn0:1 Ndx Fe1:8x  where the brackets () and [ ] denote A- and B-sites, respectively. Such a cation distribution is based on the following facts: 1. Zn2+ ions have a strong preference to occupy the A-site [19]. 2. 80% of Mn2+ ions occupy the A-site while 20% occupy the B-site [20]. 3. Rare earth ions, as Nd3+, occupy the B-site [17,18,21]. 604 M.M. Eltabey et al. 500 60 450 Initial permeability µi 40 65 20 10 0 0 1000 S x=0.00 x=0.01 x=0.02 x=0.05 x=0.075 x=0.1 60 55 350 300 250 200 150 100 50 2000 0.00 0.02 0.04 0.06 0.08 50 0.10 Nd concentration (x) 3000 4000 5000 0 300 6000 350 450 500 550 600 650 Temperature (K) H (Oe) According to the assumed cation distribution, the total magnetization (Mmol = MB  MA), where MA and MB are the magnetizations of A- and B-sites respectively, is expected to be Mmol ¼ ð6:7  1:5xÞlB ð1Þ where lB is Bohr magneton. It is valuable to note that for Mn– Zn and Ni–Zn ferrites, there exists a canting Yafet-Kittel angle (hYK) between moments in B-sites at Zn-concentration 0.4. This angle depends on the relative strength of B–B to A–B interactions [11,12,22]. In this case, the last equation could be rewritten as Mmol ¼ ð6:7 cos hYK  1:5xÞlB ð2Þ 3+ It is suggested that for 0 6 x 6 0.5, substituting Fe ions (moment = 5 lB) by Nd3+ ions (moment = 3.5 lB) leads the B-B interaction between these moments to decrease and hence the canting angle (hYK) decreases. Such a decrease in (hYK) improves the parallelism between the magnetic moments in the Bsite and leads to increase MS according to Eq. (2) to reach its maximum value at x = 0.05. For more substitution by Nd3+ ions (x > 0.05), the canting angle (hYK) could be neglected and hence MS decreases due to equation (1), where the value of magnetic moments in the B-site decreases and hence the value of MS goes down. Initial permeability Fig. 6 shows the variation of the initial permeability li with temperature for the investigated system. It is seen that the initial permeability decreases with temperature up to Curie temperature TC. There is a sharp drop in li near TC. This result could be explained according to Globus relation [23] which is given by ð3Þ where D is the average grain size and k1 is the anisotropy constant. It was reported that for Mn–Zn ferrites, the anisotropy constant is independent of temperature for temperatures higher than the room temperature [24]. Accordingly, the decrease in li with temperature can be attributed to the decrease in saturation magnetization. At TC, MS drops sharply with Fig. 6 Temperature dependence of the initial permeability for Mn0.5Ni0.1Zn0.4NdxFe2xO4. temperature leading to the rapid decrease in li. Moreover, one can notice from Fig. 6 that the slope of the linear part of li(T) curve, at the sudden decrease in li, increases with increasing Nd3+ concentration. Previous studies have reported that the value of |(dli/dT)T=Tc| gives a good indication about the sample homogeneity where higher slope corresponds to higher homogeneity [23,25]. Thus, one can conclude that the homogeneity increases with increasing Nd-concentration. The dependence of the initial permeability li, at room temperature, on Nd3+ ion concentration is represented in Fig. 7. It is clear that li increases with increasing Nd-concentration. To explain this behavior, the following aspects have to be taken in consideration. The SEM micrographs revealed that the average grain size D is nearly independent of the Nd-concentration (x). Moreover, the increase in x leads to a decrease in the iron ions concentration in the ferrite molecule. It is well known that the main source of anisotropy in ferrites is the presence of Fe2+ ions [22]. Hence, the anisotropy constant k1 decreases. This decrease in the value of k1 in turn increases li according to Globus relation. Furthermore, the enhancement of MS due to the Nd3+ ion substitution enforces the increase in li for the samples with 0 6 x 6 0.05. 650 450 400 Initial permeability µi Fig. 5 Variation of magnetization at room temperature M (emu/ g) with the magnetic field H (Oe). Inset: Variation of saturation magnetization MS (emu/g) with Nd-concentration. li aðM2s D=k1=2 1 Þ 400 600 350 550 300 250 500 µi 200 TC 450 150 Curie temperature TC (K) 30 M (emu/g) M (emu/g) x=0.00 x=0.01 x=0.02 x=0.05 x=0.075 x=0.1 400 50 100 400 0.00 0.02 0.04 0.06 0.08 0.10 Nd-concentration Fig. 7 Variation of initial permeability li, at room temperature and Curie temperature TC (K) with Nd-concentration (x). Improving the magnetic properties of Mn–Ni–Zn ferrites Values of Curie temperature (TC) were determined from the extrapolation of the linear part at the sudden decrease in li with temperature, Fig. 6, for all investigated samples. The dependence of TC on Nd3+ ion concentration is shown in Fig. 7. It is clear that TC increases considerably with increasing Nd-content (about 170 K for the sample with x = 0.05 higher than that with x = 0). For x > 0.05, TC decreases but its value is still higher than that of the un-substituted sample. One can notice from Figs. 5 and 7 that generally MS and TC behave in a same manner. The increase in TC for 0 6 x 6 0.05 with Ndconcentration could be understood in view of the behavior of both MS and the lattice parameter (a). The decrease in (a), Fig. 2, and the increase in MS, Fig. 5, with increase in the Nd-content lead to increase the A–B interaction between the moments. This in turn increases the value of TC. On the other hand, for x P 0.05, the constancy in the value of (a), Fig. 2, and the decrease in MS, Fig. 5, lead the A–B interaction between moments to decrease and, hence, TC goes down. Conclusions – Single phase Mn0.5Ni0.1Zn0.4NdxFe2xO4 ferrite samples up to x = 0.1 were obtained. – Nd3+ ions were found to concentrate in grain boundaries more than in grains, and they had no effect on both average grain size and porosity. – The saturation magnetization increased by Nd3+ substitution up to 26% relative to that of the un-substituted sample. – Both initial permeability and Curie temperature were increased due to the Nd3+ substitution from (111 to 442) and from (448 K to 627 K), respectively. Conflict of interest The authors have declared no conflict of interest. Compliance with Ethics Requirements This article does not contain any studies with human or animal subjects. Acknowledgement The authors express their deep thanks to Dr. W.A. Ghaly, Accelerators and Ion Sources Department, Nuclear Research Center, Cairo, Egypt, for his helpful advice guidance and stimulating discussions. References [1] Amarendra KS, Goel TC, Mendiratta RG. Magnetic properties of Mn-substituted Ni–Zn ferrites. J Appl Phys 2002;92:3872–6. [2] Kulkarni Suresh R. Development of In3+ substituted Mn–Ni– Zn nanoferrite core material. Arch Phys Res 2012;3(2):116–22. [3] Amarendra KS, Verma A, Thakur OP, Prakash C, Goel TC, Mendiratta RG. DC resistivity of Mn–Ni–Zn ferrites. Jpn J Appl Phys 2002;41:5142–4. [4] Japes B, Ashim KS, Aravind M. Sintering and surface microstructure of Ni–Zn ferrites. In: Proc (ICF 8), Kyoto and Tokyo, Japan; 2000. p. 536–8. 605 [5] Amarendra KS, Goel TC, Mendiratta RG. Low-temperature synthesis of Mn0.2Ni0.2Zn0.6Fe2O4 ferrites by citrate precursor method and study of their properties. Phys Status Solidi a 2004;201(7):1453–7. [6] Choi WO, Kwon WH, Lee JG, Kang BS, Chae KP. Structural and magnetic properties of nanoparticle Mn–Zn–Ni ferrite powders grown by using a sol–gel method. J Korean Phys Soc 2012;61(11):1812–6. [7] Amarendra KS, Verma A, Thakur OP, Prakash C, Goel TC, Mendiratta RG. Electrical and magnetic properties of Mn–Ni– Zn ferrites processed by citrate precursor method. Mater Lett 2003;57(5–6):1040–4. [8] Amarendra KS, Goel TC, Mendiratta RG. Effect of manganese impurity on the conductivity, dielectric behavior and magnetic properties of Ni03 MnxZn0.7x Fe2O4. Jpn J Appl Phys 2003;42:2690–1. [9] Rezlescu E, Sachelarie L, Popa PD, Rezlescu N. Effect of substitution of divalent ions on the electrical and magnetic properties of Ni–Zn–Me ferrites. IEEE Trans Magnet 2000;36(6):3962–7. [10] Shirsath SagarE, Toksha BG, Kadam RH, Patange SM, Mane DR, Jangam S, Ganesh, Ghasemi Ali. Doping effect of Mn2+ on the magnetic behavior in Ni–Zn ferrite nanoparticles prepared by sol–gel auto-combustion. J Phys Chem Sol 2010;71(12):1669–75. [11] Sattar AA, El-Sayed HM, El-Shokrofy KM, El-Tabey MM. Effect of manganese substitution on the magnetic properties of nickel-zinc ferrite. J Mater Eng and Perform 2005;14(1):99–103. [12] Sattar AA, El-Sayed HM, El-Shokrofy KM, El-Tabey MM. Improvement of the magnetic properties of Mn–Ni–Zn ferrite by the non-magnetic Al3+-ion substitution. J Appl Sci 2005;5(1):162–8. [13] Al-Kofahi MM, Al-Tarawneh KF. Analysis of Ayyubid and Mamluk dirhams using X-ray fluorescence spectrometry. X-ray Spectrom 2000;29:39–47. [14] Sattar AA, El-Sayed HM, Agami WR. Physical and magnetic properties of calcium-substituted Li–Zn ferrite. J Mater Eng Perform 2007;16:573–7. [15] Sattar AA, Wafik AH, El-Sayed HM. Infrared spectra and magnetic studies of trivalent doped Li-ferrites. Phys Status Solidi a 2001;186(3):415–22. [16] Shannon RD. Revised effective ionic radii and systematic studies of interatomic distances in halides and chalcogenides. Acta Cryst 1976;A32:751–67. [17] Rezlescu N, Rezlescu E, Pasnicu C, Craus ML. Effect of the rare-earth ions on some properties of a nickel–zinc ferrite. J Phys Condens Matter 1994;6:5707–16. [18] Rezlescu N, Rezlescu E, Popa PD, Rezlescu L. Effects of rareearth oxides on physical properties of Li–Zn ferrite. J Alloys Compds 1998;275–277:657–9. [19] Xu ZC. Magnetic anisotropy and Mössbauer spectra in disordered lithium–zinc ferrites. J Appl Phys 2003;93:4746–9. [20] Patil F, Lenglet M. Spectroscopic evidence of the Mn3+–Fe2+ octahedral pair in lithium-manganese ferrites near the order– disorder transition. Solid State Commun 1993;86:67–71. [21] Kolekar CB, Kamble PN, Vaingankar AS. Structural and dc electrical resistivity of Gd3+-substituted Cu–Cd mixed ferrites. J Magn Magn Mater 1994;138:211–5. [22] Chikazumi S, Charap S. Physics of magnetism. New York, London, Sydney: John Wiley and Sons, Inc.; 1964. [23] Globus A, Pascard H, Cagan VJ. Distance between magnetic ions and fundamental properties in ferrites. J Phys 1977;38, C1-163-8. [24] Ohta K. Magnetocrystalline anisotropy and magnetic permeability of Mn–Zn–Fe Ferrites. J Phys Soc Jpn 1963;18:685–90. [25] Sattar AA, Wafik AH, El-Shokrofy KM, El-Tabey MM. Magnetic properties of Cu–Zn ferrites doped with rare earth oxides. Phys Status Solidi a 1999;171:563–9.