Accepted Manuscript Structural and magnetic properties of Nd-Mn substituted Y-type hexaferrites synthesised by microemulsion method G. Murtaza, R. Ahmad, T. Hussain, R. Ayub, Irshad Ali, Muhammad Azhar Khan, M.N. Akhtar PII: DOI: Reference:
S0925-8388(14)00526-X http://dx.doi.org/10.1016/j.jallcom.2014.02.156 JALCOM 30741
Received Date: Revised Date: Accepted Date:
29 August 2013 4 February 2014 25 February 2014
Please cite this article as: G. Murtaza, R. Ahmad, T. Hussain, R. Ayub, I. Ali, M.A. Khan, M.N. Akhtar, Structural and magnetic properties of Nd-Mn substituted Y-type hexaferrites synthesised by microemulsion method, (2014), doi: http://dx.doi.org/10.1016/j.jallcom.2014.02.156
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Structural and magnetic properties of Nd-Mn substituted Y-type hexaferrites synthesised by microemulsion method G. Murtazaa*, R. Ahmada, T. Hussaina, R. Ayuba, Irshad Alib, Muhammad Azhar Khanc, M.N. Akhtard
a
Centre for Advanced Studies in Physics, Government College University, Lahore-54000, Pakistan
b
Department of Physics, Bahauddin Zakariya University, Multan, Pakistan
c
Department of Physics, The Islamia University of Bahawalpur, Bahawalpur-63100, Pakistan
d
Department of Physics, COMSAT, Lahore, Pakistan
Abstract Nd-Mn substituted hexaferrites of composition Sr2-xNdxNi0.5Co1.5Fe12-yMnyO22 (x = 0.0, 0.02, 0.04, 0.06, 0.08, 0.10, 0.20, 0.30, y = 0.0, 0.25, 0.50, 0.75, 1.00, 1.25, 1.50, 1.75) were synthesized using microemulsion method. The synthesized materials are characterized using different techniques including X-ray diffraction (XRD), Scanning electron microscopy(SEM), Atomic force microscopy (AFM), Fourier transform Infrared spectroscopy (FTIR), Inductance capacitance resistance (LCR) meter and Vibrating sample magnetic magnetometer (VSM). For all samples, a single Y-type phase was established and the lattice constants have been calculated. XRD patterns reveal the significant increase in line broadening which indicates a decrease of grain size. The samples exhibit well defined crystallization; all of them are hexagonal platelet grains. With the increasing substitution level of Nd-Mn, the average grain diameter decreases. The dielectric constant ε / and dielectric loss factor ε // are found to decrease initially with an increase in frequency and reached a constant value at higher frequency, exhibiting a frequencyindependent behavior at higher frequencies. The dielectric loss tangent tan δ
was found to
decrease with an increase in the frequency. The Hc decreases remarkably with increasing Nd and Mn ions content. It was found that the particle size could be effectively decreased and coercivity Hc could easily be controlled by varying the concentration (x) without significantly decreasing saturation magnetization.
Key Words: Microemulsion; Single phase; Surface morphology; Dielectric measurements; Magnetic order; 1
1. Introduction
Ferrites have continued to attract attention over years. As magnetic materials, ferrites cannot be replaced by any other magnetic materials because they are relatively inexpensive, stable and have a wide range of technological applications in transformer core, high quality filters, high and very high frequency circuits and operating devices [1]. Hexaferrites have been classified according to their structure into six main classes [2]: M-type or BaFe12O19, W-type or BaMe2Fe16O27, X-type or Ba2Me2Fe28O46, Y-type or Ba2Me2Fe12O22, Z-type or Ba3Me2Fe24O41 and U-type or Ba4Me2Fe36O60 where Me represents a small divalent ion such as those from the first transition series or Mg2+. . From the detailed studies of these ferrites, it has been established that Y-type ferrites are the first ferroxplana ferrites to be discovered because they have an easy plane (basal plane) of magnetization perpendicular to the c-axis at room temperature [2]. Initially Zn2Y and Co2Y hexaferrites were studied [3] and it has been proven that Co2Y has a planar magnetic anisotropy at room temperature. However, work on Cu2Y reveals that it is the only ferrite that has been found to have a preferred uniaxial direction [4]. It has been established that most of the hexagonal ferrites are hard magnetic materials. However, the Y-type hexagonal ferrites exhibit soft magnetic nature, which is very important in very high frequency (VHF) and ultrahigh frequency (UHF). The utilization of electronics products at higher frequency changes the senerio of applications up to Giga Hertz (GHz). For example, with the introduction of new type of chip of electronic component, such as multi-layer chip inductors (MLCI) and multi-layer chip beads (MLCB) [5], the conventional soft magnetic materials, such as NiCuZn spinel ferrite, cannot be used at higher frequency. While, Y-type hexagonal ferrites have a cut-off frequency at GHz; about one order of magnitude higher than that of spinel ferrites [6]. Therefore, Y-type hexagonal ferrite exhibits remarkable magnetic properties in hyper frequency [7] and are the best materials for chip components. *Corresponding author: E-mail:
[email protected] PH# +92-3214263536
2
Substitutions of divalent or rare-earth elements play a vital role to modify the material properties. Various elements, such as, Co-Ti, Zn-Ti, Zn-Sn, Co-Sn, La, Sm, Pr and so forth [8-12] have been used as a dopants element in barium ferrites in order to obtain suitable saturation magnetization and coercivity. In spite of this, various synthesis techniques have been used for the achievement of required better results, either structural, electrical or magnetic, etc,. Normally, the conventional ceramic technique has been utilized for the synthesis of barium ferrites. However, it often requires a higher sintering temperature, e.g. >1200 °C, which causes the agglomeration of particles [13-14]. By seeing these issues in ceramic technique, some unconventional techniques have been introduced for the growth of fine particles of barium hexaferrites. These techniques include for instance, the co-precipitation method [15-16], sol-gel method [17-19], glass-crystallization method [20], ammonium nitrate- melt technique [21], micro-emulsion [22-23] and solvent-free route method [24]. In this work, we have used microemulsion route, which is one of the most appropriate and versatile method owing to its high homogeneity and purity [25-28]. The main aim of this study is to explore the avenue towards the growth of Sr2 Ni0.5Co1.5Fe12O22 Y-type hexagonal ferrites and their characterization such as crystal structure, morphology, dielectric and magnetic properties. 2. Experimental Samples of composition Sr2-xNdxNi0.5Co1.5Fe12-yMnyO22 (x = 0.0, 0.02, 0.04, 0.06, 0.08, 0.10, 0.20, 0.30, y = 0.0, 0.25, 0.50, 0.75, 1.00, 1.25, 1.50, 1.75) were synthesized by microemulsion method. The chemical precursor used for synthesis of Y-type strontium hexaferrites were Fe(NO3)3·9H2O (Riedel-de Haen, 97%), Ni(NO3)2.6H2O (Merck, >99%), Co(NO3)2·6H2O (Merck, >99%), Sr(NO3)2 (Merck, 99%), CTAB (Merck, 97%) as a surfactant, NH3 (Fisher Scientific, 35%) as a precipitating agent and methanol (Merck, 99%) as washing agent. The metallic salt solution of the required molarities were prepared in distilled water and mixed in a beaker. The solution was stirred on the magnetic hot plate at 60 °C until it formed a clear solution. After that the precipitates were washed with deionized water and finally with methanol. The precipitates were then dried in an oven at 150 °C and finally sintered at 1000 °C for 8 h. The structural analysis of the powders was done by X-ray diffraction using a Philips 3
diffractometer and Cu K
radiation. The patterns were taken between 2Ɵ = 20° and 80° with a
step size of 0.02° and acquisition time of 5 s per step. Scanning electron microscopy (SEM) of model JEOL JSM-6480 was used to observe the microstructure of the fracture surface of the sintered specimens. The infrared spectra were recorded using FTIR instrument (IR Prestige-21 Szhamdzu) for all the samples using ATR between the range 4000 and 400 cm−1. The dielectric measurements were taken on an LCR meter Model 8101 GW INSTEK. The pellets were coated with air-drying silver paste for proper electrical contacts and the study was undertaken at room temperature with frequency range 1MHz to 3GHz. The magnetic measurements such as saturation magnetization (Ms), remanant magnetization (Mr) and coercivity (Hc) were carried out at room temperature and field range 0±1 T using a vibrating sample magnetometer (VSM, Lakeshore, Model 7300 series).
3. Results and discussions
3.1.
Structural analysis
The XRD patterns of all the synthesized samples are shown in Fig. 1. All the peaks are perfectly matched with the standard pattern (ICCD 19-100) confirming that there is no secondary phase. A slight variation in the peaks have been identified, such as, a peak indexed as (0 1 1 4) observed initially in the first three pattern and then disappear, as well as, a peak (0 2 4) appear only in the last pattern. However, these are also matched with the standard pattern (ICCD 19-100). The lattice constants (a & c), cell volume (Vcell) and crystallite size are calculated from XRD data using following relations [29]
(1)
(2)
The crystallite size is calculated by Debye–Scherer formula [25], 4
D=
Kλ βCosθ B
(3)
Where K is the shape constant having a value of 0.89 for hexagonal system, the X-rays used, intensity and
the wavelength of
is the broadening of diffraction line measured at half width of its maximum is the Bragg’s angle of diffraction.
From the Fig. 1, it is evident that XRD peaks of Nd-Mn substituted Sr2-xNdxNi0.5Co1.5Fe12yMnyO22 (x
= 0.02, 0.04, 0.06, 0.08, 0.10, 0.20 and 0.30, y = 0.25, 0.50, 0.75, 1.00, 1.25, 1.50 and
1.75,) have slightly shifted in left side (see zoomed-in mage in Fig.1) of 2 in comparison with the sample Sr2Ni0.5Co1.5Fe12O22, which indicates that Nd-Mn enter the rhombohedral lattice and change the lattice size, while keeping the rhombohedral structure rather unchanged. Table 1 list the structural parameters viz. crystal lattice a and c of samples as a function of Nd-Mn concentration. The observed variation in the lattice parameters and cell volume with Nd-Mn substitution can be associated with combined effect of the smaller size of Mn3+ ions , as we know that the ionic radius of Fe3+, Fe2+, Mn3+ and Mn2+ are 0.64, 0.76, 0.62 and 0.80 Å [5], respectively and due to the fact that Nd3+ substitution leads to the conversion of Fe3+ (0.645 Å) to Fe2+ (0.76 Å) residing on the plane axis to preserve charge neutrality [12]. This decrease in caxis and cell volume also alter few peaks, such as, 0 1 14 peak disapears due to Nd-Mn doping, while, 0 2 4 peak apears right of the 1 1 9 peak at x = 0.20, y = 1.75, which is in agreement with literature [30]. The crystallite size is found in the range of 30–46 nm as presented in Table 1. It has been reported that the crystallite size
