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STRUCTURAL PROPERTIES AND CATION DISTRIBUTION OF Co–Zn NANOFERRITES

STRUCTURAL PROPERTIES AND CATION DISTRIBUTION OF Co–Zn NANOFERRITES
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  International Journal of Modern Physics BVol. 23, No. 30 (2009) 5629–5638c  World Scientific Publishing CompanyDOI: 10.1142/S021797920905225X STRUCTURAL PROPERTIES AND CATION DISTRIBUTIONOF Co–Zn NANOFERRITES SANTOSH S. JADHAV ∗ , SAGAR E. SHIRSATH † , B. G. TOKSHA † , S. M. PATANGE † ,S. J. SHUKLA ‡ and K. M. JADHAV †∗ D.S.M.’s Arts, Commerce and Science College, Jintur 431 509, M.S., India  † Department of Physics, Dr. Babasaheb Ambedkar Marathwada University,Aurangabad 431001, M.S., India  ‡ P.G. and Research Centre, Department of Physics, Deogiri College,Aurangabad, M.S., India  ∗ drkmjadhav@yahoo.com  Received 12 June 2008The soft spinel ferrite system having the general formula Co 1 − x Zn x Fe 2 O 4  with  x  vary-ing from 0.0 to 0.7 has been prepared by wet-chemical co-precipitation technique. Theprepared samples were characterized by XRD technique. The analysis of XRD patternrevealed the formation of single-phase cubic spinel structure. The Bragg peaks in XRDpattern are broader indicating fine particle nature of the sample. XRD data have beenused to study structural parameter and cationic distribution in Co–Zn ferrite. The parti-cle size is of nanometer dimension. Cation distribution results suggest that Co 2+ occupyB-site, Zn 2+ occupy A-site, and Fe 3+ occupy both the A- and B-site. Keywords : Soft ferrites; X-ray diffraction; cation distribution.PACS numbers: 75.50.Gg, 75.75.+a, 61.10.Nz 1. Introduction Ferrites are important components in the latest electronic products, such as cellphone, computers, video cameras, etc. They acquire small dimension and lightweights and have better functions at nanoscale. Soft ferrites are of great inter-est because of their high initial permeability over a large frequency range leadingto widespread applications, e.g., inductor cores in RF system, recording heads, andmicrowave devices. Soft ferrites are commercially important materials because of their excellent magnetic and electrical properties. 1 The frustrated magnetic structure in ferrite with the spinel structure can arisewhen there is a replacement of magnetic ions by nonmagnetic ones. 2,3 The frustra-tion is necessary condition for the appearance of a canted local state, which was first ∗ Corresponding author.5629  5630  S. S. Jadhav et al. obtained by Deniels and Rossenweig. 4 Ferrite ( M  Fe 2 O 4 ,  M   = Co 2+ , Ni 2+ , Fe 2+ ,Zn 2+ , Cu 2+ , etc.) nanocrystals attract great research interest due to their poten-tial application in ferrofluids, 5–7 magnetic fluids, 8 magnetic recording media, 9 andmagnetic resonance image 10 for e.g., CoFe 2 O 4  has a high coercivity (5400 Oe) andmoderate saturation magnetization ( ∼ 80 emug − 1 ), a remarkable chemical stabil-ity, and a mechanical hardness, which make it possible material for high densityrecording media. 11,12 The effects of Zn substitution on the properties of Co andMn ferrite have been studied by Arulmurugan  et al. 13 and it was concluded thatpreparation conditions completely favor the formation of ferrites.It has been reported that the properties of nanosize dimension ferrite system andits bulk counter part are altogether different. 14 The properties exhibited by nanosizespinel ferrite are found to be superior. Keeping in view the importance of nanosizeferrite, we have synthesized Co 1 − x Zn x Fe 2 O 4  spinel ferrite system by wet-chemicalco-precipitation method and their physical properties have been investigated. In thepresent paper, we report our results on the physical properties of nanosize Co–Znspinel ferrite. 2. Experimental Method In the present work, Co 1 − x Zn x Fe 2 O 4  soft ferrite samples with composition  x  = 0 . 0–0.7 were synthesized by wet-chemical co-precipitation method. The samples wereprepared by air oxidation of an aqueous suspension containing Co 2+ , Zn 2+ and Fe 3+ cations in proper proportions. The starting solutions were prepared by mixing 50mlof aqueous solution of FeSO 4 · 7H 2 O, CoSO 4 · 7H 2 O and ZnSO 4 · 7H 2 O (all 99.9%pure supplied by s.d. fine, India) in stoichiometric proportions. A two molar (2M)solution of NaOH was prepared as a precipitant. In order to achieve simultaneousprecipitation of all the hydroxides Co(OH) 2 , Zn(OH) 2 , and Fe(OH) 2 , the startingsolution (pH  ≈  3) was added to the solution of NaOH and a suspension (pH =11) containing dark intermediate precipitates was found. Then the suspension washeated and kept at a temperature of 60 ◦ C, while oxygen gas was bubbled uniformlyinto the suspension to stir it and to promote the oxidation reaction, until all theintermediate precipitates changed into the dark brownish precipitates of the softferrite. The samples were filtered, washed several times by distilled water. Theformation of wet-chemically prepared Zn-substituted cobalt ferrite using chloridesas starting materials is reported in the literature wherein the sintering temperatureis about 700 ◦ C. 13,15 From these data, the wet samples in the present Co–Zn systemwere annealed at 725 ◦ C for 16 h.The X-ray powder diffraction patterns of powder samples were recorded onPhilips X-ray diffractometer (PW 3710) having Ni filter and Cu-K α  radiation withwavelength 1.5406˚A. The XRD patterns were in the 2 θ  range of 20 ◦ to 80 ◦ withscanning rate 1 ◦ /min. The structural parameters such as particle size, lattice con-stant were derived from XRD patterns and other physical parameters such as bondlengths, X-ray density, hopping length were also derived.  Cation Distribution of Co–Zn Nanoferrites  5631 The XRD line width and particle size are calculated through the Scherrerequation: t  = 0 . 9 λ Bcos θ B ,  (1)where  t  is the diameter of crystal particle, λ  is the wavelength of the X-ray radiation, θ B  is Bragg’s angle, B is the measure of broadening of diffraction due to size effect.The bond lengths on tetrahedral (A) site (shortest distance between A-sitecation and oxygen ion) and octahedral [B] site (shortest distance between B-sitecation and oxygen ion) can be calculated. The values of tetrahedral and octahedralbond length  d AX  and  d BX , tetrahedral edge, shared and unshared octahedral edge( d AXE ,  d BXE , and  d BXEU ) can be calculated by putting the experimental values of lattice parameter “ a ” and oxygen positional parameter “ u ” of each sample in thefollowing equations 16 : d AX  =  u −  14  a √  3 (tet. bond) ,  (2) d BX  =  a ×   3 u 2 −  114  u + 4364   (oct. bond) .  (3)The lattice edges on both tetrahedral (A) site and octahedral [B] site can becomputed from the relations: d AE  =  2 u −  12  a √  2 (tet. edge) ,  (4)( d BE ) shared  = (1 − 2 u ) a √  2 (shared octa. edge) ,  (5)( d BE ) unshared  =  a ×   4 u 2 − 3 u + 1116   (unshared octa. edge) .  (6)The pellets in cylindrical shape were prepared using a die having bore radius0.6mm. The pressure of 6ton was applied on the powder. Polyvinyl alcohol (2wt%)was added as a binder. The measured density  d m  was determined using the for-mula, 17 d m  =  mπr 2 h  (7)where  m  is the mass,  r  is the radius, and  h  is the height of the pellet.The X-ray density of all the samples of the series Co 1 − x Zn x Fe 2 O 4  has beencalculated from the molecular weight and the volume of the unit cell using theformula, 18 : d x  = 8 M Na 3  gm / cm 3 (8)where  M   is the molecular weight,  N   is Avogadro’s number, and  a  is the latticeparameter.  5632  S. S. Jadhav et al. The porosity “ P  ” of the ferrite nanoparticles was then determined using therelation, 17 P   = 1 −  d m d x ,  (9)where  d m  and  d x  are the measured densities and X-ray densities, respectively.The specific surface area was calculated from the measured diameter of theparticle and density of the sample using the relation 19 S   = 6000 td m .  (10) 3. Results and Discussion Figure 1 depicts the X-ray diffraction (XRD) patterns of the typical compositions x  = 0 . 3, 0.5, and 0.7 of the series Co 1 − x Zn x Fe 2 O 4 . The formation of single phase of  20 30405060 7080 2 θ (degree)        I     n       t     e     n     s        i       t     y        (     a     r        b  .     u     n        i       t        ) x = 0.3x = 0.5x = 0.7         (        2        2        0        )        (        3        1        1        )        (        2        2        2        )        (        4        0        0        )        (        4        2        2        )        (        3        3        3        )        (        4        4        0        )        (        6        2        0        )        (        6        2        2        ) Fig. 1. XRD patterns for the samples  x  = 0 . 3, 0.5, and 0.7 of the series Co 1 − x Zn x Fe 2 O 4 .  Cation Distribution of Co–Zn Nanoferrites  5633 Co–Zn ferrites was concluded from the XRD patterns of the investigated samples.All diffraction peaks are indexed to a pure cubic spinel phase. The lattice parameter“ a ” was calculated using the equation a  =  d   ( h 2 + K  2 + l 2 ) ,  (11)where  d  is the interplanar spacing and ( hkl ) is the index of the XRD reflectionpeak. For an accurate calculation of lattice constant “ a ” lattice parameter for eachpeak of XRD pattern was calculated and then taking average of them.The values of lattice parameter “ a ” determined from the XRD data with anaccuracy of   ± 0 . 002˚A for all the samples are listed in Table 1 as a function of Zncontent  x . Table 1 indicates that the lattice constant increases with the substitutionof Zn 2+ ions. The variation of lattice parameter “ a ” with Zn concentration “ x ” isshown in Fig. 2. It is clear from Fig. 2 that lattice parameter “ a ” increases slowlywith the addition of Zn 2+ ions. This behavior can be explained on the basis of  Table 1. Lattice constant ( a ), X-ray density ( d x ), measured density ( d m ), porosity( P  ), particle size ( t ) and specific surface area ( S  ) of Co 1 − x Zn x Fe 2 O 4 .Comp.  x a  (˚A)  d x  (gm/cm 3 )  d m  (gm/cm 3 )  P   (%)  t  (nm)  S   (m 2 /gm)0.0 8.378 5.302 4.121 22.29 27 53.9370.1 8.380 5.305 4.171 21.49 35 41.1000.2 8.384 5.307 4.213 20.81 38 37.4780.3 8.392 5.309 4.245 20.19 46 30.7270.4 8.400 5.311 4.294 19.56 47 29.7300.5 8.407 5.313 4.321 19.26 51 27.2270.6 8.417 5.314 4.341 18.31 50 27.6430.7 8.431 5.316 4.374 17.52 47 29.186 8.378.388.398.408.418.428.438.440 0.1 0.2 0.3 0.4 0.5 0.6 0.7    L  a   t   t   i  c  e  c  o  n  s   t  a  n   t   '  a   '   (    Å   ) Composition 'x' Fig. 2. Variation of lattice constant “ a ” with Zn content  x  of the seeries Co 1 − x Zn x Fe 2 O 4 .
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