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Impact of Manganese Dopant on Structural, Morphological and Magnetic properties of coated Co[Fe.sub.2][O.sub.4] nanoparticles.

INTRODUCTION

Cobalt ferrite oriented to spinel ferrite category finds considerable usages in different specializations such as gas sensors, microwave absorbers, catalysis, high density magnetic memories and biomedicine [1]. Among the nanocrystals, the cobalt ferrite possessing magneto crystalline anisotropy is an apt material to investigate the super paramagnetic characteristics and inter particle interaction due to its changes in block temperature in a long range up to room temperature [2-3]. Cobalt ferrite is one of the promising candidates for high density data storage due to its mechanical hardness, high coercive force, chemical stability and moderate saturation magnetization. It is a familiar hard magnetic material possessing high saturation magnetization and coercivity than zinc and nickel ferrites. It is mandatory and widely available magnetic material which is essential in various usages due to its remarkable properties [4]. Further, cobalt ferrite thin films are essential for the future generations because of its advancement in magneto optic recording media which is responsible for huge magneto-optical effect when compared with rare earth transition metal amorphous thin films [5]. Cobalt ferrites are the materials contains mixed characteristics of electrical insulator and magnetic conductor. They were widely investigated and being considered as an important topic because of its peculiarity in specialized fields such as magnetic data storage, antenna rods and transformer cores. The magnetic and electrical properties of spinel ferrites can be altered by incorporating different substituents, chemical composition, and way of synthesis and in accordance with particle size and particles shape [6]. Specifically, when the size of the particle get reduced to nano dimension, the cobalt ferrites exhibit super paramagnetic behaviour which finds great interest from researchers point of view in various applications [7-8]. Particularly, the nature of the other substituent, site preference of the other substituent's such as Ni, Zn, Al and Mn in cobalt ferrites greatly affects the structural, electrical and magnetic properties. Different substituents have been implemented in cobalt ferrites to investigate the electrical and magnetic properties so as to identify the variations in its characteristics [9-10]. Hence, we opt for co-precipitation method to synthesize magnetic nanoparticles. Also, as far as our knowledge, incorporating manganese in cobalt ferrites and investigating its magnetic, structural and morphological properties has not yet reported so far. Thus, we made an attempt in synthesizing cobalt ferrite nanoparticles and to analyze the impact of manganese dopant on its structural, morphological and magnetic properties via simple co-precipitation method.

II. Experimental:

A. Magnetic nanoparticles synthesis:

Stoichiometric ratio of manganese chloride, cobalt chloride and ferric chloride were dissolved in 0.1L of demineralised water in 1:2 molar ratios. The prepared solutions were added to boiling NaOH solution of 0.5M in a 5L beaker and subjected to constant mechanical stirring by top loaded stirrer. The mixture is allowed to boil for one hour at 373K.. At the end of the reaction, the mixture was uninterrupted for nearby 5hours to get clear precipitate. The residue was unperturbed by removing the demineralised water. The residue was often washed with pure water in order to bring pH in the range of 7-8 and with acetone to vanish the impurities. At the end, the product was dried to get crystalline powder and to remove the existing water traces. Thus, [Mn.sup.2+] doped coated Co[Fe.sub.2][O.sub.4] nanoparticles of various compositions ([Co.sub.1 -x][Mn.sub.x][Fe.sub.2][O.sub.4], x varying in steps of 0.2 increments) were prepared by co-precipitation method [12, 13].

B Characterization:

The structural characteristics of the synthesized [Mn.sup.2+] doped coated Co[Fe.sub.2][O.sub.4] nanoparticles of various compositions ([Co.sub.1-x][Mn.sub.x][Fe.sub.2][O.sub.4], x varying in steps of 0.2 increments) were analysed from the X-ray diffraction patterns of the samples. The XRD investigation was carried out using X'pert pro X-ray diffract meter ([lambda]=1.5406[Angstrom]) using Cu-Ka radiation in range of 10[degrees] to 80[degrees]. The morphology, size and shape of the obtained samples were identified using high resolution transmission electron microscope (HR-TEM). The magnetic characteristics such as remanence, coercivity and saturation magnetization were investigated by using vibrating sample magnetometer (VSM).

RESULTS AND DISCUSSION

To investigate the crystallographic structure, variation in lattice parameters and average crystallite size, the X-ray diffraction analyses for the [Mn.sup.2+] doped coated Co[Fe.sub.2][O.sub.4] nanoparticles of various compositions (Co1x[Mn.sub.x][Fe.sub.2][O.sub.4], x varying in steps of 0.2 increments) were carried out and it was shown in fig. 1(a-f). In [Mn.sup.2+] doped coated Co[Fe.sub.2][O.sub.4] nanoparticles the diffraction peak of the reflection plane (311) assures the cubic spinel phase. The X-ray diffraction patterns of coated magnetic nanoparticles show the reflection planes (220) (311) (400) (511) (440) of respective diffraction angles. In samples, after the incorporation of [Mn.sup.2+] dopant on Co[Fe.sub.2][O.sub.4] nanoparticles, the most intense reflection plane (311) shifts towards the lower angles (20). Further, the lattice parameter change in accordance with [Mn.sup.2[theta]] dopant on cobalt ferrite nanoparticles from 8.383[Angstorm] to 8.484[Angstorm]. The average crystallite size of the nanoparticles lies between 21nm to 42nm which was calculated by using debye scherrer's formula.

t = 0.9[lambda]/[beta]cos[theta] (1)

Where t indicates the diameter of the particles, [lambda] is the wavelength of the Cu-K[alpha] radiation, [beta] is the full width half maximum and [theta] is the Bragg's diffraction angle. The alteration in lattice parameter was due to dominance of higher atomic radii [Mn.sup.2+] ions over [Co.sup.2+] ions whose atomic radii was small during comparision. Hence, the lattice parameter shows increment while doping [Mn.sup.2+] on cobalt ferrite nanoparticles [14-15].

Fig. 2a and 2b shows the HR-TEM micrograph of coated [Co.sub.0.6][Mn.sub.0.4][Fe.sub.2][O.sub.4] nanoparticles. The image shows that the particles are most probably spherical in shape. The micrograph clearly indicates the [Mn.sup.2+] dopant on coated cobalt ferrite nanoparticles and the crystalline nature of synthesized sample. The appearance of the particles shows the impact of substituted [Mn.sup.2+] ions on coated Co[Fe.sub.2][O.sub.4] nanoparticles and it reveals the polycrystalline nature of the prepared powder samples. The agglomeration among the particles was because of its magnetic interaction between them. The particle size of coated [Co.sub.0.6][Mn.sub.0.4][Fe.sub.2][O.sub.4] nanoparticles was found to be in the range of 100nm-10nm.

Fig.3 represents the hysteresis curves of the [Mn.sup.2+] doped coated cobalt ferrites nanoparticles of various compositions prepared by co-precipitation method. Different magnetic parameters such as remanence, coercivity and saturation magnetization were estimated by using hysteresis curves obtained from the investigation of samples using vibrating sample magnetometer. It is well clear in the curves that the saturation magnetization increases for the initial dopant of manganese on cobalt ferrite nanoparticles and then the saturation magnetization begins to decrease for the increase in manganese dopant on cobalt ferrite nanoparticles. The coercivity and the magnetic retentivity otherwise called as remanence show decrement with increase in manganese dopant on cobalt ferrite nanoparticles. The variations in the above said parameters can be explained with Neel's theory and with the distribution of cations at 'A' lattice sites and 'B' lattice sites. The electron spins at A and B lattice positions are antiparallel to one another, whereas within A and B lattice positions they are parallel to one another. The total magnetization is only because of ions occupying 'B ' lattice positions in which the magnetic moment is greater than that of 'A' lattice positions. In our case, the dopant [Mn.sup.2+] which is a nonmagnetic ion replaces [Fe.sup.3+] from tetrahedral sites, the net unpaired electrons at 'B'sites gets raised which is responsible for the rise in saturation magnetization at initial stage. After 0.4 molar ratio, the saturation magnetization decreases due to much amount of non-magnetic ion occupying tetrahedral lattice positions which weakens A-B interaction. Thus the saturation magnetization decreases which was clearly indicated in hysteresis curves [16-17].

Conclusion:

In the present investigation, [Mn.sup.2+] doped coated cobalt ferrites nanoparticles of various compositions (Co1x[Mn.sub.x][Fe.sub.2][O.sub.4], x varying in steps of 0.2 increments) were prepared by co-precipitation method. X-ray diffraction patterns of all the powder samples assured the existence of cubic spinel structure. The average crystallite size estimated by using debye scherrer's formula was identified to be in the scale of 21-42nm and the changes in lattice parameter was found to be in the range of 8.383[Angstorm] to 8.484[Angstorm] which was in good coincidence with the previous investigations. The HR-TEM images exhibit the crystalline nature and morphology of the particle arrangement. It proves the details regarding the composition and the particle size which was identified to be in between 20-100nm. The saturation magnetization show gradual decrement with increase in [Mn.sup.2+] dopant on coated cobalt ferrites nanoparticles in initial stage and it shows increment in final stages which indicates the [Mn.sup.2+] dominance on coated cobalt ferrite nanoparticles in tetrahedral lattice positions. Further, the decrement in remanence and coercivity proves the dominance of non-magnetic [Mn.sup.2+] dominance on coated cobalt ferrite nanoparticles.

ACKNOWLEDGMENT

Dr. S. Sendhilnathan appreciatively acknowledges the DST (Ref. no. SERC no.100/IFD/7194/2010-11 dated 12.10.10) for the financial assistance received through the project.

REFERENCES

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(1) M. Margabandhu, (2) S. Sendhilnathan, (3) Hirthna

(1) University College of Engineering-Ariyaiur, Department of Physics, Ariyalur -621704, India.

(2) University College of Engineering-Pattukkottai, Department of Physics, Rajamadam-614701, Thanjavur, India.

(3) University College of Engineering-Kanchipuram, Department of Physics, Kanchipuram-631552, Tamilnadu, India.

Received 28 February 2017; Accepted 22 May 2017; Available online 6 June 2017

Address For Correspondence: M. Margabandhu, University College of Engineering-Ariyalur, Department of Physics, Ariyalur-621704, India.

Caption: Fig. 1a

Caption: Fig. 1b

Caption: Fig. 1c

Caption: Fig. 1d

Caption: Fig. 1(a-f): X-ray diffraction patterns of [Mn.sup.2+] doped Co[Fe.sub.2][O.sub.4] nanoparticles of various (Coi-x[Mn.sub.x][Fe.sub.2][O.sub.4], x varying in steps of 0.2 increments) chemical compositions

Caption: Fig. 2(a-b): HR-TEM images of [Co.sub.0.6][Mn.sub.0.4][Fe.sub.2][O.sub.4] nanoparticles

Caption: Fig. 3: Magnetization curves of Coi-x[Mn.sub.x][Fe.sub.2][O.sub.4] nanoparticles with x varying from 0 to 1.
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Author:Margabandhu, M.; Sendhilnathan, S.; Hirthna
Publication:Advances in Natural and Applied Sciences
Article Type:Report
Date:Jun 1, 2017
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