Microstructural and Mössbauer properties of low temperature synthesized Ni-Cd-Al ferrite nanoparticles
© Batoo; licensee Springer. 2011
Received: 4 May 2011
Accepted: 18 August 2011
Published: 18 August 2011
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© Batoo; licensee Springer. 2011
Received: 4 May 2011
Accepted: 18 August 2011
Published: 18 August 2011
We report the influence of Al3+ doping on the microstructural and Mössbauer properties of ferrite nanoparticles of basic composition Ni0.2Cd0.3Fe2.5 - x Al x O4 (0.0 ≤ x ≤ 0.5) prepared through simple sol-gel method. X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray, transmission electron microscopy (TEM), Fourier transformation infrared (FTIR), and Mössbauer spectroscopy techniques were used to investigate the structural, chemical, and Mössbauer properties of the grown nanoparticles. XRD results confirm that all the samples are single-phase cubic spinel in structure excluding the presence of any secondary phase corresponding to any structure. SEM micrographs show the synthesized nanoparticles are agglomerated but spherical in shape. The average crystallite size of the grown nanoparticles was calculated through Scherrer formula and confirmed by TEM and was found between 2 and 8 nm (± 1). FTIR results show the presence of two vibrational bands corresponding to tetrahedral and octahedral sites. Mössbauer spectroscopy shows that all the samples exhibit superparamagnetism, and the quadrupole interaction increases with the substitution of Al3+ ions.
Nanoparticles of spinel ferrites have attracted great interest for a long time in fundamental science, especially in addressing the fundamental relationships between magnetic properties and their crystal chemistry and structure. Since nanoparticles have often novel properties that are different from their bulk properties due to their small size, they are becoming a core component of advanced materials that have wide practical applications with noble optical, electrical, magnetic, and catalytic properties [1, 2]. Superparamagnetism is a unique feature of magnetic nanoparticles and is crucially related to many modern technologies, including ferrofluid technology , magnetic refrigeration , etc.
Ferrites are ferrimagnetic oxides, crystallizes into two magnetic sub-lattices, tetrahedral (A) site and octahedral (B) site. The electrical and magnetic properties, upon which their application depends, depend upon the cation distribution among these two sites. Ferrites are high-resistivity materials with low eddy current losses which make them potential materials for high-frequency applications such as microwave devices. The electrical resistivity of ferrites has been normally found to increase on doping or substituting with other oxides .
Several novel and non-equilibrium processing methods such as rapid solidification from the liquid state, mechanical alloying, plasma processing, vapor deposition, etc. have been developed during the past few decades to convert the microcrystalline materials to nanocrystalline materials in order to improve the physical and mechanical properties of the existing materials . For example, magnetic behavior as a physical property is optimum in the nanocrystalline materials relative to conventional materials. It is well-known that the microstructure, especially the crystallite size, essentially determines the hysteresis loop of the soft ferromagnetic materials . In the last two decades, various mechanical routes for producing ferrite magnetic powders (ferrites and metallic alloys) were introduced . Mechanical alloying is one of the routine processes or preparation route of nanocrystalline structures by utilizing high-energy ball milling of materials to achieve alloys or composite materials with desired microstructures [8–10].
Ni-Cd ferrite, is a soft magnetic material, with a spinel crystal structure with widespread applications in recording heads, antenna rods, loading coils, microwave devices, core material for power transformers due to their high resistivity and low eddy current losses [11–13]. Nanocrystalline soft ferrites exhibit high coercivities and low saturation magnetization compared to the other conventional ferrites .
Cadmium is known to show strong preference for (A) sites in spinel ferrites. Consequently, CdFe2O4 is a normal spinel. On the other hand, NiFe2O4 is an inverse spinel where Ni2+ and Fe3+ occupy the octahedral and tetrahedral sites, respectively. With the mixing of Ni2+ with Cd2+ to form Ni-Cd ferrite, some of Fe3+ ions migrate to octahedral positions and complexes of Fe3+/Cd2+ reside in tetrahedral sites and Fe3+/Ni2+ reside in octahedral sites [15–17]. Many reports on the synthesization of Ni-Cd ferrites are limited to ceramic techniques or solid state reaction methods [18–24]. To the best of our search we did not found any report on the synthesization of Ni-Cd ferrite nanoparticles though chemical route method. Among the various chemical route methods known, such as co-precipitation , sol-gel auto combustion , sol-gel , citrate-gel precursor  polymer pyrolysis , microemulsion , egg white , solvothermal method , hydrothermal , reverse micelle , the sol-gel method allows good control over the size of the material particles, which in turn decides their structural and transport properties (electrical and magnetic). The advantage of this method includes processing at low temperature, mixing at molecular level and fabrication of novel materials.
In the present work, we report the influence of f Al3+ doping and grain size over microstructural, and Mossbauer properties of Ni0.2Cd0.3Fe2.5 - x Al x O4 ferrite nanoparticles using X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive X-ray (EDX), Fourier transformation infrared (FTIR), and Mössbauer spectroscopy techniques.
Ferrite nanoparticles with chemical formula Ni0.2Cd0.3Fe2.5 - x Al x O4 (0.0 ≤ x ≤ 0.5) were prepared through sol-gel method, using analytical grade chemicals: Ni(NO3)2.6H2O, Cd(NO3)2.4H2O, Al(NO3)3.9H2O, and Fe(NO3)2.9H2O as starting materials. Stoichiometric mixtures of the abovementioned materials were dissolved in deionized water and few drops of ethyl alcohol were added to it. Few drops of N, N-dimethylformamide C3H7NO (M.W.73.10) were added to the solution, to obtain the fine crystalline particles. The solution was allowed for gel formation on the magnetic stirrer at 75°C with constant stirring until gel was obtained. The gel formed was annealed at 90°C for 19 h followed by grinding for half an hour. The powder formed was heated for 36 h at 400°C to remove any organic material present and ground for half an hour .
PANanalytical X'Pert Pro X-ray diffractometer (PANalytical B.V., Almelo Netherland, instrument located at King Abdullah Institute for Nanotechnology, Riyadh, Saudi Arabia) with Cu Kα (λ = 1.54 Å) was used to study the single-phase nature and nanophase formation of the pure and doped Ni-Cd-Al ferrite nanoparticles at room temperature.
The microstructural analysis of the samples was carried out using a field emission scanning electron microscope (JSM 7600F, JEOL USA, Inc., instrument located at King Abdullah Institute for Nanotechnology, Riyadh, Saudi Arabia) and high-resolution transmission electron microscope (HRTEM) (Jeol 2010, JEOL USA, Inc., instrument located at King Abdullah Institute for Nanotechnology, Riyadh Saudi Arabia).
The IR measurements were carried out using Fourier transformation infrared spectrophotometer, Nicolet Impact 410 DSP (Nicolet Instrument Corp., instrument located at School of Nano and Materials Engineering, Changwon National University, South Korea) carried out in the range of 400 to 4,000 cm-1.
Mössbauer spectra of the nanoparticle samples were recorded at room temperature using Canberra series 30 multichannel analyzer with 25 mCi Co57 source (Canberra Industries, Inc. Meriden, CT, USA). The calibration of the spectrometer was done using standard natural iron absorber.
where Γ is the average crystalline dimension perpendicular to the reflecting phases, λ the X-ray wavelength, θ the Bragg's angle, and (L)vol the volume-weighted average column length, i.e., the number of reflecting planes times their effective distance "d." For spherical particle (L)vol equals 0.75(D)vol, where D is the grain diameter. The average crystallite sizes of all the samples were determined using a (301) diffraction peak broadening technique and is found to be in the range of 3 nm to approximately 7 nm (± 1).
The EDX parameters of Ni0.2Cd0.3Fe2.5 - x Al x O4 (0.0 ≤ x ≤ 0.5) ferrite nanoparticles
Chemical composition (EDX)
( x )
The two strong bands that appear around 579 cm-1 and 420 cm-1 are the characteristic bands of Ni0.2Cd0.3Fe2.5 - x Al x O4 ferrite revealing the formation of Ni-Cd-Al ferrite. The absorption band ν 1 appears around 579 cm-1 and the absorption band ν 2 appears around 420 cm-1. The difference between ν 1 and ν 2 is due to the changes in bond length (Fe-O) at octahedral and tetrahedral sites . The spectra also show a shift due to the introduction of Al3+ ions. The tetrahedral site bands are shifted from lower band values to higher band values, i.e., from 574.32 to 579.21 cm-1, which is attributed to the stretching of Fe-O bonds on substitution of Al ions. The octahedral band sites on the contrary shift towards lower frequency region from 429.24 to 417.51 cm-1 with Al addition, which is attributed to the shifting of Fe towards oxygen ion on occupation of octahedral sites by Al ions .
Mössbauer parameter of the Ni0.2Cd0.3Fe2.5 - x Al x O4 ferrite nanoparticles at room temperature
Isomer shift δ (mm/s)
Quadrupole splitting Δ E (mm/s)
x = 0.0
x = 0.2
x = 0.3
x = 0.4
Nanoparticles of Ni0.2Cd0.3Fe2.5Al x O4 ferrites were synthesized through the sol-gel method. The FTIR results show the presence of two vibrational modes corresponding to tetrahedral and octahedral sites. Mössbauer spectroscopy results confirm that all the samples exhibit superparamagnetism. The samples show the presence of paramagnetic doublet due to quadrupole interaction. The intensity of the paramagnetic doublet increases with increasing concentration of Al3+ ions or with decreasing particle size.
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