Accepted Manuscript Research articles Characterization and structural and magnetic studies of as-synthesized Fe2+Cr x Fe(2- x )O4 nanoparticles M.A. Amer, A. Matsuda, G. Kawamura, R. El-Shater, T. Meaz, F. Fakhry PII: DOI: Reference:
S0304-8853(16)33356-X http://dx.doi.org/10.1016/j.jmmm.2017.05.048 MAGMA 62752
To appear in:
Journal of Magnetism and Magnetic Materials
Received Date: Revised Date: Accepted Date:
14 December 2016 2 May 2017 15 May 2017
Please cite this article as: M.A. Amer, A. Matsuda, G. Kawamura, R. El-Shater, T. Meaz, F. Fakhry, Characterization and structural and magnetic studies of as-synthesized Fe2+Cr x Fe(2- x )O4 nanoparticles, Journal of Magnetism and Magnetic Materials (2017), doi: http://dx.doi.org/10.1016/j.jmmm.2017.05.048
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
1
Characterization and structural and magnetic studies of as-synthesized Fe2+CrxFe(2-x)O4 nanoparticles M.A. Amer a,*, A. Matsudab, G. Kawamurab, R. El-Shater a, T. Meaz a, F. Fakhry a a b
Physics Department, Faculty of Science, Tanta University, Tanta 31527, Egypt
Electrical and Electronic Information Engineering Department, Toyohashi University of Technology, Toyohashi 441-8580, Japan
Abstract As-synthesized Fe2+CrxFe(2-x)O4 nanoferrites, 0.0 ≤ x ≤ 1, were prepared by the wet-chemical coprecipitation route and characterized by the X-ray diffraction, Brunauer-Emmett-Teller and transmission electron microscopy, IR spectra, thermographometry and vibrating sample magnetometry (VSM) techniques. This study proved that these samples have single phase of cubic spinel structure in nano-metric scale and are ferrimagnetic materials. VSM measurements revealed that these nanoferrites are soft ferrimagnetic materials. The crystallite size R, porosity P, strain ε, Debye temperature, nanoparticle specific surface area, B-site force constant, elastic parameters and sheer and longitudinal velocities were increased with increasing the Cr3+ ion content x, whereas the lattice constant, density, grain specific surface area and A-site force constant were decreased. The strain ε proved dependence on P and R. Six absorption bands were observed in IR spectra and assigned to their corresponding sites and bonds. Thermal analysis of the samples displayed three steps of combustion process where the net loss of weight ranged 19%-33%. The saturation magnetization MS of the samples was decreased against x, whereas the coercivity HC was increased. Two peaks at 710 and 723 eV appeared in XPS spectra and attributed to Fe 2p3/2 and Fe 2p1/2. They reveal that the ratio of Fe2+ to Fe3+ ions increases with Cr ion increment. Keywords: As-synthesized Fe2+CrxFe(2-x)O4 nanoferrites; Magnetic properties; Resonant frequency; Debye temperature; XPS spectra.
*Corresponding author e-mail:
[email protected] &
[email protected]
2
1 Introduction The nano-ferrite materials became attractive field to the researchers for investigation of the medical, technical and academic requirements because of their specific physical, structural, magnetic, thermal and chemical properties which differ from that of bulk ferrite materials. This provides us a wide variety of interesting technological applications and promising fields such as magnetic and microwave devices, computer components, magnetic refrigeration, satellite communications, RADAR, detoxification of biological fluids, magnetically controlled transport of anti-cancer drugs, magnetic resonance imaging (MRI), sensors, etc [1-5]. The properties of nano ferrites depend on their preparation method, chemical composition, metallic ion charges and radii, crystal structure and grain size. The spinel nanostructure is considered the most interesting kind due to variation in its physical properties considerably by different metallic ions [1-5]. Most published articles have discussed the variation in physical and chemical properties depending on the preparation method, substitution process and ionic radii and charges [1-7]. The cation distribution among the tetrahedral A-sites and octahedral B-sites is important factor affected the physical and chemical properties of the bulk and nano ferrites [8]. R.M. Sebastian et al [9] have studied the electric and magnetic properties of the cubic spinel ZnCrxFe2-xO4 nanoferrites, which were prepared by the sol-gel method. They reported that the lattice constant and grain size were decreased against the Cr3+ ion content. Some researchers [5,10] have synthesized the cubic spinel CuCrxFe2-xO4 nanoferrites by the co-precipitation method. They have reported that the lattice constant and x-ray density showed decrease with x, whereas the grain size, bulk density and porosity did not show dependence on x. L.Z. Li et al [11] have prepared Ni0.5-xZn0.5CrxFe1,9O4 by the sol-gel auto-combustion method. DTA/TGA charts illustrated three steps of combustion process, which are the endothermic peak, dehydration of the precursor and exothermic peak. The authors have attributed these steps to decomposition process and oxidative decomposition of the residual matter. Some researchers [12] have studied the magnetite material and considered it as a mixed-valence compound having the chemical formula (Fe3+) [Fe2+Fe3+]O4, where the A-sites are occupied by Fe3+ ions and the B-sites are occupied by equal numbers of Fe2+ and Fe3+ ions.
3
It is well known that Cr3+ ions exclusively occupy the octahedral B-sites of the cubic spinels, while Fe ions can occupy both the tetrahedral and octahedral sites [1-4,12]. Increasing the Cr3+ ions among the B-sites leads to pushing Fe ions into the tetrahedral A-sites, which alters the different properties and affects cation distributions of the nanoferrites. Therefore, the present research is concerned on studying the mixed Fe2+CrxFe(2-x)O4 nanoferrites synthesized by the wet-Chemical Co-precipitation method and studying the effect of substitution process on their physical properties. The samples were characterized by XRD, TEM, BET, FT-IR, DTA/TG and VSM techniques.
2 Experimental Samples of spinel Fe2+CrxFe(2-x)O4 nano-ferrite system, where x = 0, 0.2, 0.4, 0.6, 0.8 and 1, were synthesized by the wet-chemical Co-precipitation method as reported early [5,6]. Stoichiometric amounts of the high purity salts; ferric chloride, ferrous chloride and chromium chloride were dissolved in deionized water and mixed under stirring. Then NaOH solution was added to the mixture as drop-wise under stirring until PH value reached to 10. The solution was heated to about 80 ºC for 2 hours till the co-precipitation occurs. Then, the precipitates were washed many times with deionized water to remove the unwanted residual salts. Afterward, the samples were dried at around 150 ºC for four hours, and ground to fine powder in agate mortar [5,6]. X-ray diffraction patterns were recorded for all the samples using computerized x-ray diffractometer of the type Shimadzu 7000 Maxima and Cu Kα1 radiation with wave length λ = 1.540568 Å. A computer program was used to deduce diffraction angle θ, full width at half maximum of the diffraction peak β1/2 and interplanar distance according to Brag’s relation; 2dsinθ = nλ. The lattice constant a of the cubic ferrite system was calculated according to Bragg’s equation [1];
= ( ℎ + + ) where h, k and l are the miller indices. The specific surface area of the nanoparticles was measured by the Brunauer-Emmett-Teller (BET) Micrometrics Instrument Corporation TriStar II 3020 V1.03. The specific surface area of the grains was determined using the transmission electron microscope of the kind JEOL-TEM-
4
2100F microscope with 200KV. The Fourier-transform infrared spectra were recorded by Bruker Tensor 27 in the range 200–2000 cm-1 at room temperature (RT). The force constant (FC) was calculated by the equation [5];
= 4 C
where C is the velocity of light, ν is the sublattice frequency and m is the reduced mass of Fe and O ions (2.061x10-23g). Differential thermal analysis and thermo-gravimetric (DTA/TG) was measured in the range from RT to 1200 ºC at 5 ºC/min heating rate by using Rigaku Thermo Plus EVO2. The magnetic hysteresis loops of the samples were recorded at room temperature by the Vibrating Sample Magneto TM-(VSM) 261483-HGC with maximum applied magnetic field of 12 KOe. XPS spectra were taken by Ulvac-Phi QuanteraSXM with AlKα. A C-C peak at 284.8 eV was used for charge correction.
3 Results and discussion 3.1 X-ray diffraction (XRD) analysis XRD patterns of the system Fe2+CrxFe(2-x)O4, x = 0, 0.2, 0.4, 0.6, 0.8 and 1, are shown in Fig. 1. The observed peaks in the patterns reveal a single phase of cubic spinel structure of the samples which is confirmed by comparing with JCPDS cards (JCPDS card no. 22-1086). Broadening the diffraction peaks and decreasing their intensity with x may be due to small crystallite sizes, large strains and inter-lattice spacing inside the crystal lattices, where the samples tend to be amorphous with increasing Cr3+ ion concentration [4]. Small diffraction peaks are observed in the XRD patterns which may be due to existence of smaller crystallites in the samples. A small diffraction peak is observed at around 67o for the samples x = 0.4 and 0.6. This peak may assign to formation of hematite phase in these samples (α-Fe2O3). In addition to this peak, the diffraction peak (111) appeared only for the samples x =0.6 and 0.8. These peaks may be attributed to the formation of ferromagnetically ordered nanoclusters in these spinel nanoferrites [13,14], where the structure of this nanocluster is the same structure of the spinel nanomaterial with slight little lattice parameters [13,14]. The obtained values of lattice constant a are plotted against x as displayed in Fig. 2. The obtained values of a lie in the range of 8.2995 8.3455 Å. It is displayed that a changes nonmonotonically against x due to the motion of metallic
5
ions between the tetrahedral A-sites and octahedral B-sites by the substitution process, but the trend of a values increases slowly with Cr3+ content x. The increase in a may assign to the substitution of the Cr3+ (0.615 Å) ions at the expense of Fe3+ (0.645 Å) ions at the B-sites, where the Cr3+ ions exclusively accommodate in the B-sites [1-4]. Increasing the Cr3+ ion content x in the B-sites creates some chemical disorder in the crystal lattice and pushes the lager Fe2+ (0.78 Å) ions into the A-sites that enlarges the A-site radius to accommodate these larger Fe2+ ions. This leads to increasing the strain inside the crystal lattice and to increasing a.
Fig. 1 XRD patterns of as-prepared spinel Fe2+CrxFe(2-x)O4 nanoferrites (JCPDS card no. 22-1086).
The crystallite size R was calculated using the full width at half maximum of the diffraction peak (β1/2) and Debye-Scherer’s equation [1]; R = 0.9λ/β1/2cosθ The obtained values of R lie in the range of 5.148 – 13.21 nm, which agree well with reported values for nanoferrites [6-16]. Fig. 3 illustrates that R increases with increasing the Cr3+ ion
6
concentration x, which may be due to the effect of increasing chemical disorder and large strain in the samples [15].
Fig. 2 Variation of both crystallite size R and lattice constant a against x.
The hopping length L (the distance between magnetic ions) at the A-sites (LA-A), B-sites (LB-B) and shared sites (LA-B) can be deduced by the relations [2,6,7]: √
√
LA-A = a , LB-B = a
&
√
LA-B = a
The deduced values are tabulated in Table 1which explains that the hopping lengths behave as a. Table 1 Hopping lengths at the A-sites (LA-A), B-sites (LB-B) and shared sites (LA-B).
x
LA-A(Å)
LB-B(Å)
LA-B(Å)
0
3.5975
2.9411
1.492942
0.2
3.5967
2.9405
1.49262
0.4
3.6004
2.9435
1.4942
0.6
3.5985
2.942
1.4934
0.8
3.5937
2.938
1.4914
1
3.6136
2.9543
1.4997
The theoretical (x-ray) density Dx was calculated by the equation [1,3,16];
7
=
where Z is the number of molecules per unit cell (Z = 8); M is the molecular weight and NA is Avogadro’s number. The porosity P was calculated by the equation [16]; =1−
where D is the experimental density. Fig. 3 displays that Dx and D decrease slowly with x, which may be due to the substitution of Fe3+ ions (55.845) by the lighter Cr3+ ions (51.996) [1]. It is displayed that P increases with x which may be due to increase in R and differences in variation of D and Dx [16,17].
Fig. 3 Variation of the density D, theoretical density Dx and porosity P with x.
The lattice strain ε is determined by the equation [5,17,18]; !( /) cos & =
0.9* + 4, sin θ +
The specific surface area (S) of the grain is calculated by the equation [18]; S=
01234 5617289 2192 01234 :255
=
;
