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A Peer-reviewed Offic S Size Induced Structural Ferrites Synt Bekam Dengia Nagasa 1 , Ra 1 Department of Physics, Col 2 Department of Physics, Narasaraop 3 Department of Chemistry, Co Cobalt ferrite (CoFe2O4), a well-known hard high frequency applications and high-dens thermal stability, high permeability, high e coercivity etc. they found wide technologic include catalytic properties, electrochem properties. Thermally induced changes synthesized by co-precipitation technique. be the most economical and successful t having narrow particle size distribution. The using X-ray diffraction (XRD), scanning magnetometer (VSM) measurements. The increase from 23 to 65 nm as the annealin lattice parameters were observed to increas energy (E) of nanostructured CoFe2O4 temperature has a prominent effect on the coercivity and remanence were observed t work, we plan to synthesize nanocrystal understand the role of synthesis techniques [email protected]5 S INTRODUCTION Nanocrystalline spinel ferrites are because of their novel propertie understanding the fundamental propertie fact, there are number of studies w magnetic properties at the atomic leve structural properties and the rich crysta ferrites offer excellent opportunities for u fine tuning the magnetic properties (C The cation distribution of spinel ferrite the type of chemical environment, synthesis techniques, crystallite size a process. The magnetic properties of CoFe2 are determined by many factors composition, type of crystal lattice, sh and interactions of particles with su (Zhang et al., 2004). By changing th shape, composition, and structure, on magnetic properties. However, these always be controlled during synthesis cial International Journal of Wollega University DOI: http://dx.doi.org/10 ISSN: 2226-7522(Print) and 2 Science, Technology and Arts R Sci. Technol. Arts Res. J., Jan-March Journal Homepage: http://ww and Magnetic Properties of Nanostr thesized by Co-precipitation Techni aghavender A.T 1* , Kebede Legesse Kabeta Melkamu Biyane Regasa 3 llege of Natural and Computational Sciences, Wo Post Box No: 395, Nekemte, Ethiopia pet Engineering College, Narasaraopet - 522 601 ollege of Natural and Computational Sciences, W Post Box No: 395, Nekemte, Ethiopia Abstract d magnetic material. It is also one of the candidates for sity recording media. Due to their good chemical and electrical resistivity, high saturation magnetization and cal applications. Size dependent properties of CoFe2O4 mical properties, magnetic properties and optical in nanocrystalline CoFe2O4 spinel ferrites were Unlike other techniques, co-precipitation is reported to technique for synthesizing ultrafine CoFe2O4 powders eir structural and magnetic properties were investigated g electron microscopy (SEM) and vibrating sample e average crystallite size of CoFe2O4 was observed to ng temperature was increased from 300 to 900°C. The ase due to increase in the crystallite size. The activation was observed to be 11.6 kJ/mol. The annealing e nanocrystallite growth. The saturation magnetization, to increase with increasing crystallite size. In our future lline CoFe2O4 using different techniques in order to s on the structural and magnetic properties. STAR Journal, Wollega University. All Rights Reserved. of great interest es and also in es point of view. In which explains the el. In addition, the allography of spinel understanding and Chen et al., 1996). es is influenced by doping elements, and the annealing 2O4 nanomaterials s like chemical hape, morphology urrounding matrix he crystallite size, ne can control the e factors cannot of nano materials. Therefore, the properties of na same type of ferrites are differen CoFe2O4 materials have been their high excellent chemical st saturation magnetization, me electromagnetic properties, wh suitable candidate for the rec cards and in electronic comp Sugimoto, 1999 and Fan et al., In this present work, w nanocrystalline cobalt ferrite technique which is one of the m consumes very less time over o The results of crystallite size magnetic properties of cobalt detail. MATERIALS AND METHOD Nanostructured CoFe2O4 w precipitation technique (Rag Orig 84 y, Ethiopia 0.4314/star.v4i1.13 2305-3372 (Online) Research Journal h 2015, 4(1): 84-87 ww.starjournal.org/ ructured Cobalt ique a 1 , Anjaneyulu T 2 , ollega University, 1, Andhra Pradesh, India Wollega University, Article Information Article History: Received : 20-02-2015 Revised : 24-03-2015 Accepted : 28-03-2015 Keywords: Nanomaterials Co-precipitation technique Cobalt ferrite Structural properties Magnetic properties *Corresponding Author: Raghavender A.T E-mail: [email protected] anomaterials even for the nt. In the last few decades, widely investigated due to tability, high coercivity and echanical hardness, and hich make this material a cording devices, magnetic ponents (Alivisatos, 1996; 2009). we aimed to synthesize es using co-precipitation most economical routes and other synthesis techniques. dependent structural and ferrites are presented in DS were synthesized using co- ghavender et al., 2011; ginal Research

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  • A Peer-reviewed Official International Journal

    Sci. Technol. Arts Res.

    Size Induced Structural Ferrites Synthesized by Co

    Bekam Dengia Nagasa1, Raghavender

    1Department of Physics, College of Natural and

    2Department of Physics, Narasaraopet Engineering College, Narasaraopet 3Department of Chemistry, College of Natural and

    Cobalt ferrite (CoFe2O4), a well-known hard magnetic materialhigh frequency applications and high-density recording media. Due to their good chemical and thermal stability, high permeability, high electrical resistivity, high saturation magnetization and coercivity etc. they found wide technological applications. Size dependent properties of Cinclude catalytic properties, electrochemical properties, magnetic properties and optical properties. Thermally induced changes in nanocrystalline CoFesynthesized by co-precipitation technique. Unlike other techniques, cobe the most economical and successful technique for synthesizing ultrafine CoFehaving narrow particle size distribution. Their structural and magnetic properties were investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM) and vibrating sample magnetometer (VSM) measurements. The average crystallite size of CoFeincrease from 23 to 65 nm as the annealing temperature was increased from 300 to 900C. The lattice parameters were observed to increase due to increase in the crystallite size. The activation energy (E) of nanostructured CoFe2O4 temperature has a prominent effect on the nanocrystallite growth. The saturation magnetization, coercivity and remanence were observed to increase with increasing work, we plan to synthesize nanocrystalline CoFeunderstand the role of synthesis techniques on the structural and

    [email protected] STAR Journal

    INTRODUCTION

    Nanocrystalline spinel ferrites are of great interest because of their novel properties and understanding the fundamental properties point of view. In fact, there are number of studies which explains the magnetic properties at the atomic level. In addition, the structural properties and the rich crystallography of spinelferrites offer excellent opportunities for understanding and fine tuning the magnetic properties (Chen The cation distribution of spinel ferrites is the type of chemical environment, doping elements, synthesis techniques, crystallite size and the annealing process.

    The magnetic properties of CoFe2

    are determined by many factors like chemical composition, type of crystal lattice, shape, morphology and interactions of particles with surrounding matrix (Zhang et al., 2004). By changing the shape, composition, and structure, one can control the magnetic properties. However, these factors cannot always be controlled during synthesis of nano materials.

    Official International Journal of Wollega University, Ethiopia

    DOI: http://dx.doi.org/10.4314/star.v4i1.

    ISSN: 2226-7522(Print) and 2305

    Science, Technology and Arts Research Journal

    Sci. Technol. Arts Res. J., Jan-March

    Journal Homepage: http://www.starjournal.org/

    and Magnetic Properties of Nanostructured Synthesized by Co-precipitation Technique

    Raghavender A.T1*, Kebede Legesse KabetaMelkamu Biyane Regasa3

    Department of Physics, College of Natural and Computational Sciences, Wollega University,

    Post Box No: 395, Nekemte, Ethiopia

    Department of Physics, Narasaraopet Engineering College, Narasaraopet - 522 601,

    Department of Chemistry, College of Natural and Computational Sciences, Wollega University,Post Box No: 395, Nekemte, Ethiopia

    Abstract known hard magnetic material. It is also one of the candidates for

    density recording media. Due to their good chemical and thermal stability, high permeability, high electrical resistivity, high saturation magnetization and coercivity etc. they found wide technological applications. Size dependent properties of CoFe2O4 include catalytic properties, electrochemical properties, magnetic properties and optical properties. Thermally induced changes in nanocrystalline CoFe2O4 spinel ferrites were

    precipitation technique. Unlike other techniques, co-precipitation is reported to be the most economical and successful technique for synthesizing ultrafine CoFe2O4 powders

    Their structural and magnetic properties were investigated ng electron microscopy (SEM) and vibrating sample

    magnetometer (VSM) measurements. The average crystallite size of CoFe2O4 was observed to increase from 23 to 65 nm as the annealing temperature was increased from 300 to 900C. The

    bserved to increase due to increase in the crystallite size. The activation 4 was observed to be 11.6 kJ/mol. The annealing

    temperature has a prominent effect on the nanocrystallite growth. The saturation magnetization, ved to increase with increasing crystallite size. In our future

    nanocrystalline CoFe2O4 using different techniques in order to understand the role of synthesis techniques on the structural and magnetic properties.

    STAR Journal, Wollega University. All Rights Reserved.

    Nanocrystalline spinel ferrites are of great interest properties and also in

    understanding the fundamental properties point of view. In which explains the

    atomic level. In addition, the rystallography of spinel

    offer excellent opportunities for understanding and Chen et al., 1996).

    The cation distribution of spinel ferrites is influenced by , doping elements,

    size and the annealing

    2O4 nanomaterials are determined by many factors like chemical

    lattice, shape, morphology and interactions of particles with surrounding matrix

    the crystallite size, shape, composition, and structure, one can control the magnetic properties. However, these factors cannot

    trolled during synthesis of nano materials.

    Therefore, the properties of nanomaterials even fsame type of ferrites are different. ICoFe2O4 materials have been their high excellent chemical stabilitysaturation magnetization, mechanical hardness, electromagnetic properties, which makesuitable candidate for the recording devices, magnetic cards and in electronic componentsSugimoto, 1999 and Fan et al., 2009).

    In this present work, we aimed to synthesize

    nanocrystalline cobalt ferrites using cotechnique which is one of the most economical routes and consumes very less time over other synthesis techniques. The results of crystallite size dependent structural and magnetic properties of cobalt ferrites are presented in detail.

    MATERIALS AND METHODS

    Nanostructured CoFe2O4 were synthesized using coprecipitation technique (Raghavender

    Original Research

    84 of Wollega University, Ethiopia

    http://dx.doi.org/10.4314/star.v4i1.13

    7522(Print) and 2305-3372 (Online)

    Science, Technology and Arts Research Journal

    March 2015, 4(1): 84-87

    http://www.starjournal.org/

    Nanostructured Cobalt precipitation Technique

    , Kebede Legesse Kabeta1, Anjaneyulu T2,

    Wollega University,

    522 601, Andhra Pradesh, India

    Wollega University,

    Article Information Article History:

    Received : 20-02-2015

    Revised : 24-03-2015

    Accepted : 28-03-2015 Keywords:

    Nanomaterials

    Co-precipitation technique

    Cobalt ferrite

    Structural properties

    Magnetic properties

    *Corresponding Author:

    Raghavender A.T E-mail: [email protected]

    Therefore, the properties of nanomaterials even for the same type of ferrites are different. In the last few decades,

    widely investigated due to high excellent chemical stability, high coercivity and

    mechanical hardness, and which make this material a

    candidate for the recording devices, magnetic electronic components (Alivisatos, 1996;

    , 2009).

    In this present work, we aimed to synthesize nanocrystalline cobalt ferrites using co-precipitation technique which is one of the most economical routes and consumes very less time over other synthesis techniques.

    crystallite size dependent structural and magnetic properties of cobalt ferrites are presented in

    MATERIALS AND METHODS

    were synthesized using co-precipitation technique (Raghavender et al., 2011;

    Original Research

  • Bekam Dengia Nagasa et al., Sci. Technol. Arts Res. J., Jan-March 2015, 4(1): 84-87

    85

    Berhanu et al., 2014). The AR grade sodium hydroxide (NaOH), Cobalt (II) nitrate hydrate (Co(NO3)2.6H2O), ferric (III) nitrate nonahydrate (Fe(NO3)3. 9H2O) (98%) were used as starting materials. The metal nitrates were dissolved together in minimum amount of deionized water to get a clear solution. NaOH solution was added drop by drop to metal nitrates solution under vigorous stirring. The precipitation occurred immediately to change the reaction solution to dark brown. The entire reaction was carried out at 75 C for 2 h. The pH of the solution was varied by NaOH. The resulting precipitates were washed with deionized water and ethanol several times. The resulting precipitates was dried at 200 C for 3h. The structural characterization of precipitates powders was carried out using Philips (France) X-ray diffraction (XRD) system with Ni filter using Cu K radiation (wave length = 1.54 Ao). The morphology was verified using FEI Quanta (USA) FEG 200 High Resolution Scanning Electron Microscope (HR-SEM). Room temperature magnetic properties were investigated using Lakeshore (USA) vibrating sample magnetometer (VSM 7410).

    RESULTS AND DISCUSSIONS

    Figure 1 shows the X-ray diffraction patterns of CoFe2O4 samples annealed at temperatures from 300 to 900 C. The crystallite size was observed to increase from 23 to 65 nm due to increase in the annealing temperature as shown in Figure 2 and Table 1. The crystallite size was evaluated from the most intense (311) peak employing the Scherrer formula

    cos

    9.0=D

    (1) where is the angular line width at half maximum

    intensity and is the Bragg angle for the actual peak.

    Figure 1: X-ray diffraction patterns of CoFe2O4 samples

    annealed at temperatures (a) 300 C, (a) 500 C, (a) 700 C and (a) 900 C

    Table.1: Dependence of crystallite size (D), lattice constants (a), saturation magnetization (Ms), remanence magnetization (Mr), coercivity (Hc ) and remanence ratio (Mr / Ms)

    Temp. (C)

    D (nm)

    a ()

    Ms (emu/g)

    Mr (emu/g)

    Hc (Oe)

    Mr / Ms

    300 23 8.299 9.13 5.09 915 0.56

    500 31 8.304 18.2 9.87 979 0.54

    700 54 8.308 23.3 10.42 1386 0.44

    900 65 8.314 27.4 13.86 1850 0.5

    The increase in the crystallite size is due to increase in the volume of the grains. When the particles are in nanoregime, due to increase in the annealing temperature the grain growth takes place (Kumar et al., 2008). As observed from Figure 1, the XRD lines are broad and the broadening of the peaks decreases with increasing annealing temperature. Further, the increase in the intensity of X-ray diffraction shows improved crystallinity and gradual increase in the crystallite sizes of CoFe2O4 as a function of heat treatment process.

    The lattice constants were calculated from the most

    intense (311) peak of the XRD and the corresponding values are presented in Table. 1. The lattice constants were observed to be nearly equal to that of bulk CoFe2O4. The lattice constants were observed to increase from 8.299 to 8.314 with increasing annealing temperature from 300 to 900 C as shown in Figure 2 and Table 1. The observed change in the lattice constants with annealing temperature is the evidence of structural changes taking place in CoFe2O4 (Singh et al., 2004). This can be explained in terms of a meta-stable cation distribution in nanocrystallies. Since on increasing the annealing temperature the crystallite size D increases, the lattice constants a is expected to increase (Chen et al., 1996, Oliver et al., 2000).

    400 600 80020

    40

    60

    Crystallite size Lattice constants

    Temperature ( 0C)

    D (nm)

    8.300

    8.304

    8.308

    8.312

    8.316

    a (0A)

    Figure 2: Dependence of crystallite size (D) and lattice constants (a) on the annealing temperatures of CoFe2O4 samples

    The annealing temperature has prominent effect on

    the CoFe2O4 crystallite size. This is directly related to the crystallization of the nanocrystals. A straight line of ln (d) against 1/T (Figure 3) is plotted according to the Scott equation given below under the condition of homogeneous growth rate of nanocrystallite (Scott, 1983; Yang et al., 2004). The Scott equation approximately describes the growth rate of nanocrystallites from thermal treatment of amorphous compound:

    d = C exp (-E / RT) (1)

    where d is the XRD crystallite size, C is a constant, E

    is the activation energy for grain growth, R is the ideal gas constant and T is the absolute temperature.

    10 20 30 40 50 60 700

    1000

    2000

    d

    cb

    a

    (440)

    (333)

    (422)(400)

    (222)

    (311)

    (220)

    (111)

    I [ a.u ]

    2[ 0 ]

  • Bekam Dengia Nagasa et al.,

    0 .8 1 .0 1.2 1.43 .0

    3 .2

    3 .4

    3 .6

    3 .8

    4 .0 y = -1 .19x + 4 .97

    103 / T (K

    -1)

    ln (d)

    Figure 3: Plot of ln(d) against 1/T. Line presents a linear fit for ln(d) vs 1/T dependence

    There exists a good linear relationship between lnand 1/T. E values could be calculated from the slope of the straight line, presented in Figure 3 as It can be considered that the grain grows primarily by means of an interfacial reaction. It also shows that growth

    Figure 4: SEM images of CoFe

    The room-temperature hysteresis loops for the samples annealed at temperatures from shown in Figure 5. The derived parametershysteresis loops are presented in Table. 1magnetization (Ms) for the sample annealed observed to be 9.13 emu/g, which is very much smaller than the saturation magnetization of bulk annealing temperature increased to 900Cmagnetization attains the value of 27.4 emu/g,comparable to the saturation magnetization value of CoFe2O4 synthesized from other techniques(Raghavender, 2013). The discrepancymagnetization in our case might be due to several facts such as, synthesis technique and conditionsused, annealing temperature, grain / particle size, size (Singh, 2013).

    The saturation magnetization values for samples was observed to increase with increase in crystallite size. This kind of behavior CoFe2O4 (Shafi et al., 1998; Gharagozlouet al., 1988), NiFe2O4 (Zhang et al., 2004;2007), and MnFe2O4 (Muroi et al., 2001)other techniques. When the crystallite size increasesredistribution of cations in the lattice takes place reported to influence the magnetic properties of (Wang, 2006 and Kodama et al., 1996). It is clearly observed that the saturation magnetization depends strongly on the crystallite size. The magnetization for ferromagnetic material usually increases with

    Sci. Technol. Arts Res. J., Jan-

    1.4 1.6

    y = -1 .19x + 4 .97

    ) against 1/T. Line presents a linear

    There exists a good linear relationship between lnd values could be calculated from the slope of

    the straight line, presented in Figure 3 as E = 11.6 kJ/mol. It can be considered that the grain grows primarily by means of an interfacial reaction. It also shows that growth

    of Cobalt ferrite nanocrystals areannealing temperature, which is confirmed from Figure 3. Our activation value E = 11.6 kJ/mol is much less than 18.5 kJ/mol for CoFe2O4 prepared by ball milling (Yang al., 2004).

    Figure 4 presents the SEM

    samples annealed at 500 and 900 suggest that, there is slight agglomeration among particles. The nanocrystals distinctly exhibit narrow particle size distribution and present mainly sphericity. The SEM image of the sample Figure 4(a)) show the microstructure with fairly smallgrain size. As the annealing temperature was increased to 900 C, a non-uniform grain growth with the presence of intragranular pores were observed (annealing temperature may lead to abnormal grain growth and closed pores. These kinds of pores were generally accounted for poor physico-mechanical properties andwhich may have significant affect on the magnetic properties.

    SEM images of CoFe2O4 samples annealed at temperatures (a) 500 C and (b) 900 C.

    temperature hysteresis loops for the at temperatures from 300 to 900C are

    parameters from the loops are presented in Table. 1. The saturation

    annealed at 300C is emu/g, which is very much smaller

    the saturation magnetization of bulk CoFe2O4. As the temperature increased to 900C, the

    4 emu/g, which is comparable to the saturation magnetization value of

    from other techniques discrepancy in the observed

    magnetization in our case might be due to several facts and conditions, chemical

    particle size, cluster

    saturation magnetization values for of CoFe2O4 increase with increase in

    kind of behavior was observed for Gharagozlou, 2009; Haneda

    2004; Sepelak et al., 2001) synthesized by

    size increases, the takes place and is

    reported to influence the magnetic properties of ferrites 1996). It is clearly

    that the saturation magnetization depends . The magnetization for creases with increasing

    crystallite size (Ahmed et al., 2009). Tis valid for remanence magnetization also.

    -10 -5 0-30

    -20

    -10

    0

    10

    20

    30

    M [ emu /g ]

    H [ kOe ]

    300 0C

    500 0C

    700 0C

    900 0C

    Figure 5: Room temperature magnetizationmeasurements for CoFeat different temperatures

    Coercivity (Hc) was observed to increase

    1850 Oe as the crystallite size increased from 23 to 65 nm. The coercivity was observed to depend strongly on the crystallite size. The Mr magnetization to saturation magnetization) decreased with increase in the crystallite indicates the fraction of superparamagnetic particles in the synthesized samples and the decrease in these values may be due to the existence of spin canting (Jiang et al., 1999).. One of the possibilities of spin canting may

    -March 2015, 4(1): 84-87

    86

    ferrite nanocrystals are easily effected by annealing temperature, which is confirmed from Figure 3.

    = 11.6 kJ/mol is much less than prepared by ball milling (Yang et

    4 presents the SEM images of CoFe2O4 samples annealed at 500 and 900 C. The SEM images

    there is slight agglomeration among the particles. The nanocrystals distinctly exhibit narrow particle size distribution and present mainly sphericity. The SEM image of the sample annealed at 500 C (See Figure 4(a)) show the microstructure with fairly smaller grain size. As the annealing temperature was increased to

    uniform grain growth with the presence of anular pores were observed (Figure 4(b)). Higher

    lead to abnormal grain growth and closed pores. These kinds of pores were generally

    mechanical properties and affect on the structural and

    samples annealed at temperatures (a) 500 C and (b) 900 C.

    2009). The same argument magnetization also.

    0 5 10H [ kOe ]

    Room temperature magnetization measurements for CoFe2O4 samples annealed at different temperatures

    was observed to increase from 915 to size increased from 23 to 65

    he coercivity was observed to depend strongly on / Ms ratio (remanent magnetization) decreased size. The Mr / Ms , values

    indicates the fraction of superparamagnetic particles in the synthesized samples and the decrease in these values may be due to the existence of spin canting (Jiang

    1999).. One of the possibilities of spin canting may

  • Bekam Dengia Nagasa et al., Sci. Technol. Arts Res. J., Jan-March 2015, 4(1): 84-87

    87

    be due to surface and interface effect (Ahmed et al., 2009). The remanent ratio Mr / Ms, is a characteristic parameter of the material and is dependent on the anisotropy (Singh et al., 2004), indicating the ease with which the magnetization direction is reoriented to the nearest easy axis magnetization direction after the magnetic field is removed. The lower the Mr / Ms ratio, the more isotropic the material will be. The values of Mr / Ms varied from 0.56 to 0.44 with increase in crystallite size except for the 65 nm particles. The observed variation in the coercivity field and remanence ratio with crystallite size can be explained on the basis of domain structure, critical size, and the anisotropy of the crystal (Qu et al., 2006; Vasic et al., 2006 and George et al., 2006). It is worth mentioning that the magnetic properties of nanocrystalline CoFe2O4 depends on the synthesis technique and conditions. CONCLUSIONS

    Nanocrystalline CoFe2O4 were successfully synthesized using co-precipitation technique. The structural and magnetic properties were investigated using X-ray diffraction, scanning electron microscopy and magnetization measurements. The average crystallite size of CoFe2O4 was observed to increase from 23 to 65 nm as the annealing temperature was increased from 300 to 900C. The lattice parameters were observed to increase with increasing crystallite size due to changes in the structural properties. The magnetic properties exhibit a strong dependence on the crystallite size. Magnetization was observed to increase from 9.13 to 27.4 emu/g. The coercivity was observed to increase from 915 to 1850 Oe.

    Conflict of Interest

    Authors declared no conflict of interest.

    REFERENCES Ahmed, Y.M.Z., Hessien, M.M., Rashad, M.M., Ibrahim, I.A.

    (2009). Nano-crystalline copper ferrites from secondary iron oxide (mill scale). Journal of Magnetism and Magnetic Materials 321: 181-187.

    Alivisatos, A.P. (1996). Semiconductor clusters, nanocrystals, and quantum dots. Science 271:933-37.

    Berhanu, H., Raghavender, A.T., Kebede, L., Anjaneyulu, T. (2014). Ferromagnetic Behavior in Zinc Ferrite Nano -particles Synthesized using Coprecipitation Technique. Science Technology Arts Research Journal 3: 85-88.

    Chen, J.P., Sorensen, C.M., Klabunde, K.J., Hadjipanayis, G. C., Devlin, E., Kostikas, A. (1996). Size-dependent magnetic properties of MnFe2O4 fine particles synthesized by coprecipitation. Physical Review B 54: 9288-9296.

    Fan, H-M., Yi, J-B., Yang, Y., Kho, K-W., Tan, H-R., Shen, Z-X., Ding, J, Sun, X-W., Malini, M.C., Feng, Y.P. (2009). Single-crystalline MFe2O4 nanotubes/ nanorings synthesized by thermal transformation process for biological applications. ACS Nano 3: 2798-2808.

    George, M., Mary John, A., Nair, S.S., Joy, P.A., Anantharaman M. R. (2006). Finite size effects on the structural and magnetic properties of sol-gel synthesized NiFe2O4 powders. Journal of Magnetism and Magnetic Materials 302: 190-195.

    Gharagozlou, M. (2009). Synthesis, characterization and influence of calcination temperature on magnetic properties of nanocrystalline spinel Co-ferrite prepared by polymeric precursor method. Journal of Alloys and Compounds 486: 660-665.

    Haneda, K., Morrish, A. H. (1988). Noncollinear magnetic structure of CoFe2O4 small particles Journal of Applied Physics 63: 4258-4260.

    Jiang, J.Z., Goya, G.F., Rechenberg, H.R. (1999). Magnetic properties of nanostructured CuFe2O4. Journal of Physics: Condensed Matter 11: 4063-4078.

    Kodama, R.H., Berkowitz, A.E., McNiff, Jr E.J., Foner, S. (1996). Surface Spin Disorder in NiFe2O4 Nanoparticles. Physical Review Letters 77: 394-397.

    Kumar, V., Rana, A., Yadav, M.S., Pant, R.P. (2008). Size-induced effects on nanocrystalline CoFe2O4. Journal of Magnetism and Magnetic Materials 320: 1729-1734.

    Muroi, M., Street, R., McCormick, P.G., Amighian, P. (2001). Magnetic properties of ultrafine MnFe2O4 powders prepared by mechanochemical processing Physical Review B 63: 184414-184417.

    Oliver, S.A., Harriss, V.G., Hamdeh, H.H., Ho, J.C. (2000). Large zinc cation occupancy of octahedral sites in mechanically activated zinc ferrite powders. Applied Physics Letters 76: 2761-2763.

    Qu, Y., Yang, H., Yang, N., Fan, Y., Zhu, H., Zou, G. (2006). The effect of reaction temperature on the particle size, structure and magnetic properties of coprecipitated CoFe2O4 nanoparticles. Materials Letters 60: 3548-3552.

    Raghavender, A.T. (2013). Synthesis and Characterization of Cobalt Ferrite Nanoparticles. Science Technology and Arts Research Journal 2: 01-04.

    Raghavender, A.T., Nguyen Hoa Hong. (2011). Dependence of Nel temperature on the particle size of MnFe2O4. Journal of Magnetism & Magnetic Materials 323: 2145-47.

    Scott, M.G. (1983). Amorphous Metallic Alloys, Butterworths, London, Pp. 151.

    Sepelk, V., Bergmann, I., Feldhoff, A., Heitjans, P., Krumeich, F., Menzel, D., Litterst, F.J., Campbell, S.J., Becker, K.D. (2007). Nanocrystalline Nickel Ferrite, NiFe2O4: Mechanosynthesis, Nonequilibrium Cation Distribution, Canted Spin Arrangement, and Magnetic Behaviour Journal of Physics and Chemistry C 111: 5026-5033.

    Shafi, K.V.P.M., Gedanken, A., Prozorov, R. (1998). Sonochemical preparation and size-dependent properties of nanostructured CoFe2O4 particles Journal of Balogh Chemistry Materials 10: 3445-3450.

    Singh, A.K., Goel, T.C., Mendiratta, R.G. (2004). Low-temperature synthesis of Mn0.2 Ni0.2 Zn0.6 Fe2O4 ferrites by citrate precursor method and study of their Properties. Physica Status Solidi (a) 201: 1453 - 1457.

    Singh R. J. (2013). Unexpected magnetism in nanomaterials. Journal of Magnetism and Magnetic Materials 346: 58-73.

    Sugimoto M., (1999). The past, present, and future of ferrites. Journal of the American Ceramic Society 82: 269280.

    Vasic, M., Antic, B., Kremenovic, A. (2006). Zn,Ni ferrite/NiO nanocomposite powder obtained from acetylacetonato complexes. Nanotechnology 17: 4877-4884.

    Wang, J. (2006). Prepare highly crystalline NiFe2O4 nanoparticles with improved magnetic properties. Material Science Engineering B 127: 81-84.

    Yang, H., Zhang, X., Huang, C., Yang, W., Qiu, G. (2004). Synthesis of ZnFe2O4 nanocrystallites by mechano chemical reaction. Journal of Physics and Chemistry of Solids 65: 1329-1332.

    Zhang, Y.D., Ge, S.H., Zhang, H., Hui, S., Budnick, J.I., Hines, W.A., Yacaman, M.J., Miki, M. (2004). Effect of spin disorder on magnetic properties of nanostructured Ni-ferrite. Journal of Applied Physics 95: 7130-7132.