Structural, Magnetic and Photoluminiscent Properties of Strontium Ferrite Nanoparticles synthesized using Citrate precursor method

Rakesh kumar Singh , A. Yadav , R. S. Yadav , A. C. Pandey

Deptt. of Physics, Patna Women’s College, Patna University School of Pure Sciences (PG section), Nalanda Open University, Patna
Nanophosphor Centre,
University of Allahabad.


Abstract

Strontium ferrite nanoparticles were synthesized using chemical based citrate precursor method. In this method, nitrates of divalent metal, trivalent metal iron and citric acid were taken in molar ratio. Citrate precursor was annealed at temperature 450 0C and 650 0C in a muffle furnace that lead to ferrite powder after crushing. The powder samples were characterized using X-ray diffraction (XRD), Vibrating sample magnetometer (VSM) and Photoluminiscence spectrometer(PL). The mean particle size observed was 15.7 nm at 450 0C and 20.3 nm at 650 0C. The lattice constant was found to increase from 10.663Å to 10.667? . Coercivity and Retentivity are also found to increase but saturation magnetization was found to decrease.
Photoluminisence (PL) property of this sample was studied using 225nm, 250nm and 330nm excitation wavelength radiation source. The PL spectrum was obtained in visible range only by excitation through 225 nm and 250 nm radiation source.
Key words: Hexa-ferrite, Nanoparticles, Photoluminence, Magnetic behaviour

Introduction:

Strontium ferrite having general formula SrFe12 O19 is a famous magnetic material which has a variety of applications in microwave devices and in permanent magnet1,2. The electromagnetic wave absorption property of hexaferrite with a magnetoplumbite structure in the GHz range, which includes M-, W-, Y-, Z-, U- and X-type has found demands for microwave communication, microwave dark room target camouflage, electromagnetic radiation abatement, and so on3 .In nanocrystalline form hexaferrites are of particular interest for use as high density perpendicular magnetic recording media 4,5. Photoluminescence (PL) is nondestructive method of probing the electronic structure of material. The intensity & spectral content of this PL is a direct measure of various important material properties. The important applications are in materials quality,
  impurity levels and defect detection, band gap determination and recombination mechanism.
Many processes have been used to prepare strontium ferrite, including the solid state method7, Solgel 8,9 and coprecipitation 10 and other chemical processes11 . Among these processes, coprecipitation and sol-gel methods are more popular for the preparation of hard ferrite nanomaterials. Recently, the nanocrystalline Sr ferrite with mean particle size below 100nm has been prepared by sol-gel process using PVA( Polyacrylic acid) as a stabilizer.12 However such a small particles size is still difficult to achieve by simple coprecipitation method. We have prepared small particle of size found 15.7nm at annealing temperature 450 0C and 20.3nm at 650 0C. The method of preparation was used Citrate precursor method.
Materials and Methods:

Samples of nanometer-sized Strontium hexaferrite powder were prepared by using the Citrate precursor method. Ferric nitrate, Strontium nitrate and Citric acid were taken in Stoichiometric proportion as starting materials. Aqueous solutions of these salts were prepared separately by dissolving the salt in minimum amount of deionized water while stirring constantly. The solutions were then mixed together. The mixture was heated to temperature between 60oC to 80oC for two hours with continuous stirring. This solution was allowed to cool to room temperature and finally it was dried overnight in oven in order to remove excess water and other impurities at 90-95oC until it formed a brown color fluffy powder. The Citrate precursor was heated at temperature 450oC & other sample at temperature 650oC for one hour in a muffle furnace. By this process, the precursor thermally decomposed to give Strontium hexaferrite powder of nanometer size.

Result and Discussion

Ferrite powders were characterized using X-ray diffractometer (XRD) for phases and mean particles size. The X-ray diffraction spectra shown in figures 1 & 2. We have chosen maximum intensity peak for particle size calculation and particle size observed was 15.7 nm and 20.3 nm at annealing temperature 450oC & 650oC respectively.
ge
The magnetic measurement of these nanometric particles was done using vibrating sample magnetometer. The magnetization curve are shown in
dfg
  figures 3 & 4. The magnetic parameters are tabulated in table 1.
dfg
Fig 3: Hysteresis curve for Sr ferrite nanoparticles annealed at 450 0C. Fig 4: Hysteresis curve for Sr ferrite nanoparticles annealed at 650 0C
Table 1: Observed data for Sr ferrite nanoparticles.
dfg
dg
Figure 5: Photoluminescence spectrum of Strontium ferrite nanoparticles ( annealed at 450 0C ) under 225, 250 and 330 nm excitation. df
Figure 6: Photoluminescence spectrum of Strontium ferrite nanoparticles ( annealed at 650 0C ) under 225, 250 and 330 nm excitation.
The magnetic parameters such as coercivity, saturation magnetization, and retentivity of sample Strontium ferrite nanoparticles were obtained using VSM as 75.539G, 36.615emu/g, and 3.321emu/g at annealing temperature 4500C while 157.04 G, 36.149 emu/g and 5.665 emu/g at annealing temperature 6500C respectively. In the preparation of hexaferrite, a high annealing temperature is required to obtain pure phase . This results in significant increases of particle size together with improvement of ion occupancy13. Jun Wang et al. have reported that the Barium hexaferrite nanoparticles formed at 140oC in presence spectrum also should include the effect of the surface oxide and nonhomogenous sizes generally if there is a difference in the energies, which is associated with the stokes shift between the absorption- surface defects or surface oxide. The mechanism of charge transfer between the trivalent ion appears to involve a nonradiative, superexchange process via the intervening oxide ions, that support the ferromagnetic ordering18 . As follows from the above discussion, the situation with the PL mechanism is very complex and is difficult to draw a definite conclusion about the PL mechanism at this stage. Further studies are needed in order to elucidate the correct mechanism of PL in hexa ferrite Nanoparticles.

Conclusion We have prepared small particle size using Citrate precursor method. The annealing temperature 4500C & 6500C are also low in this method. The Coercivity and retentivity both increase with temperature while saturation magnetization slightly decreases. PL spectra in visible region shows only by excitation through 225 nm and 250nm radiation source. PL spectrum shows different colours in visible region and their intensities also found to decrease.

Acknowledgement: This research work was supported by the Nalanda Open University, Patna, India. We are thankful to Prof. H.C.Verma, Deptt of Physics, I.I.T Kanpur and Dr. R.K.Kotnala, National Physical laboratory New Delhi for constant encouragement.

References:

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