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Magnetocrystalline anisotropy of NiCoFe2O4 nanoparticles
Ceramics International 42 (2016) 9315–9318
Contents lists available at ScienceDirect
Ceramics International journal homepage: www.elsevier.com/locate/ceramint
Short communication
Magnetocrystalline anisotropy of NiCoFe2O4 nanoparticles Ronaldo Sergio de Biasi a,b,n, Rayanne Dezio de Souza Lopes a,b a b
Departamento de Engenharia Mecânica e de Materiais, Instituto Militar de Engenharia, Praça General Tiburcio, 80, 22290-270 Rio de Janeiro, RJ, Brazil Seção de Engenharia Mecânica e de Materiais, Instituto Militar de Engenharia, 22290-270 Rio de Janeiro, RJ, Brazil
art ic l e i nf o
a b s t r a c t
Article history: Received 10 November 2015 Received in revised form 17 February 2016 Accepted 23 February 2016 Available online 24 February 2016
Nanosized particles of Ni1 xCoxFe2O4 were synthesized by the sol–gel combustion method and the physical properties of these mixed ferrites were studied by X-ray diffraction and ferromagnetic resonance. The average crystallite size in samples with different Ni–Co ratios was determined from the X-ray diffractograms, whereas ferromagnetic resonance spectra were used to study the dependence of the magnetocrystalline anisotropy on the relative concentration of nickel and cobalt. According to the X-ray diffractograms, the samples are single phase and the crystallite size is between 9 and 22 nm. The ferromagnetic resonance spectra showed that the magnetocrystalline anisotropy of the samples is positive, except for pure NiFe2O4, and increases monotonically with Co concentration, a result that could be of interest for practical applications. & 2016 Elsevier Ltd and Techna Group S.r.l. All rights reserved.
Keywords: A. Sol–gel processes C. Magnetic properties D. Ferrites
1. Introduction
2. Experimental procedure and results
Nanosized ferrites have important technological [1,2] and biomedical [3,4] uses. Mixed ferrites are a common approach to optimize the magnetic properties of the material for particular applications. Since the magnetocrystalline anisotropies of nickel ferrite and cobalt ferrite have opposite signs, one can adjust the magnetic anisotropy of nickel–cobalt ferrite over a wide range by changing the relative amounts of nickel and cobalt. In the present work, we made a series of samples of composition Ni1 xCoxFe2O4, using the sol–gel/combustion method [5], and determined the magnetocrystalline anisotropy of the material by ferromagnetic resonance. X-ray diffraction was used to estimate the average crystallite size. Although the saturation magnetization of this mixed ferrite has been previously studied by other researchers [6], this is the first time, to our knowledge, that the magnetocrystalline anisotropy of NiCoFe2O4 nanoparticles is investigated in a systematic way.
2.1. Sample preparation Stoichiometric amounts of analytical grade Fe(NO3)3 9H2O, Ni(NO3)2 6H2O and Co(NO3)2 6H2O were dissolved in deionized water to obtain the starting solution. To this was added a 0.75 M solution of citric acid (C6H8O7 H2O). The resulting solution was stirred for 4 h at 60 °C, heated to 80 °C and kept at this temperature until the sol turned into a transparent gel. The gel was then heated to 200 °C for 20 min so that auto-combustion would take place. 2.2. X-ray measurements X-ray diffractograms were recorded in a PANalytical X'Pert PRO diffractometer using Cu Kα radiation. The diffraction patterns of Ni1 xCoxFe2O4 samples, for x ¼0, 0.2, 0.4, 0.6, 0.8 and 1.0, are shown in Fig. 1. The patterns for x¼ 0 and x¼ 1 matched, respectively, the ICSD patterns 084677 (NiFe2O4) and 066759 (CoFe2O4). The average crystallite sizes shown in Table 1 are estimated using the Debye–Scherrer equation
d= n
Corresponding author at: Departamento de Engenharia Mecânica e de Materiais, Instituto Militar de Engenharia, Praça General Tiburcio, 80, 22290-270 Rio de Janeiro, RJ, Brazil. E-mail addresses: [email protected] (R.S. de Biasi), [email protected] (R.D. de Souza Lopes). http://dx.doi.org/10.1016/j.ceramint.2016.02.141 0272-8842/& 2016 Elsevier Ltd and Techna Group S.r.l. All rights reserved.
0. 9 λ B cos θ
(1)
where d is the average crystallite size, λ is the X-ray wavelength, B is the linewidth at half the line intensity and θ is the Bragg angle. We used for B the average value for the five most intense lines in the diffractograms, labeled in the bottom diffractogram of Fig. 1.
9316
R.S. de Biasi, R.D. de Souza Lopes / Ceramics International 42 (2016) 9315–9318
Fig. 1. X-ray diffraction patterns of Ni1 xCoxFe2O4 samples for several values of x.
Table 1 Average crystallite size of Ni1 xCoxFe2O4 samples. x
Composition
d (nm)
0.0 0.2 0.4 0.6 0.8 1.0
NiFe2O4 Ni0.8Co0.2Fe2O4 Ni0.6Co0.4Fe2O4 Ni0.4Co0.6Fe2O4 Ni0.2Co0.8Fe2O4 CoFe2O4
19 22 18 17 16 9
2.3. Ferromagnetic resonance measurements Ferromagnetic resonance measurements were performed at room temperature and 9.50 GHz using a Varian E-12 spectrometer with 100 kHz field modulation. The microwave power was 5 mW and the modulation amplitude was 1 mT. The magnetic field was calibrated with an NMR gaussmeter. The ferromagnetic resonance spectra of Ni1 xCoxFe2O4 samples are shown in Fig. 2(a)–(e) for x ¼0, 0.2, 0.4, 0.6, 0.8 and 1.0. The experimental results were fitted to theoretical spectra using a computer program developed by Taylor and Bray [7] for paramagnetic resonance spectra and adapted by Griscom [8] for ferromagnetic resonance spectra. The fitting was generally good, except for the low field part of the spectra, where the slope of the amplitude rise is much steeper in the experimental curves. This
mismatch is attributed [9] to superparamagnetic effects. The fitting parameters are shown in Table 3 and the dependence of the anisotropy field on cobalt concentration is shown in Fig. 3. The magnetocrystalline anisotropy of the samples was computed from the anisotropy field using equation [8]
K = 2πMs HA
(2)
where Ms is the saturation magnetization of the nanoparticles. The values of Ms were taken from the literature [6] and the values of HA were taken from Table 2; the results are shown in Table 3 and Fig. 4. Since [10] the anisotropy of bulk cobalt ferrite is large and positive ( þ2 105 J/m3) and the anisotropy of bulk nickel ferrite is small and negative ( 0.062 105 J/m3), it is expected that the anisotropy of Ni–Co ferrites be positive, except for small cobalt concentrations, and increase with increasing Co content.
R.S. de Biasi, R.D. de Souza Lopes / Ceramics International 42 (2016) 9315–9318
9317
Fig. 2. Ferromagnetic resonance spectra of samples of Ni1 xCoxFe2O4 for several values of x.
That is exactly what was found in the present work (see Table 3 and Fig. 4); the values of K range from 1.15 105 J/m3 for x ¼0.0 to þ2.25 105 J/m3 for x¼ 1.0. The fact that the absolute value of the anisotropy of nickel ferrite nanoparticles is much larger than that of its bulk counterpart may be attributed to a different cation distribution related to the preparation method, but this question should be investigated further using other experimental methods, such as Mössbauer spectroscopy.
3. Conclusions The physical properties of particles of the mixed ferrite Ni1 xCoxFe2O4 prepared by the sol–gel/combustion method were investigated using the X-ray diffraction and ferromagnetic resonance techniques. The X-ray results showed that the samples are single phase and that the crystallite size is in the nanometer range. The ferromagnetic resonance results showed that the magnetocrystalline
9318
R.S. de Biasi, R.D. de Souza Lopes / Ceramics International 42 (2016) 9315–9318
anisotropy of the samples increases monotonically with Co concentration, a result that could be of interest for practical applications.
Acknowledgments The authors thank CAPES and CNPq for financial support.
References
Fig. 3. Anisotropy field of Ni1 xCoxFe2O4 for several values of x. The lines are only guides to the eye. Table 2 Ferromagnetic resonance parameters of Ni1 xCoxFe2O4 samples. x
g-Factor
Anisotropy field (T)
Intrinsic linewidth (T)
0.0 0.2 0.4 0.6 0.8 1.0
2.10 2.10 2.10 2.10 2.10 2.10
0.0715 0.0400 0.0600 0.0752 0.0782 0.0800
0.2950 0.2690 0.2448 0.2100 0.1820 0.1800
Table 3 Parameters used in the calculation of the anisotropy constant of Ni1 xCoxFe2O4 samples. x
Density (g/ cm³)
MS (emu/g)
MS (A/m)
Anisotropy field (T)
Anisotropy constant (J/m3)
0 0.2 0.4 0.6 0.8 1.0
5.380 5.362 5.344 5.326 5.308 5.290
47.6 53.9 61.5 69.3 74.7 84.5
2.56 105 2.89 105 3.28 105 3.69 105 3.96 105 4.47 105
0.0715 0.0400 0.0600 0.0752 0.0782 0.0800
1.15 105 0.73 105 1.24 105 1.74 105 1.95 105 2.25 105
Fig. 4. Magnetocrystalline anisotropy of Ni1 xCoxFe2O4 for several values of x. The lines are only guides to the eye.
[1] M. Younas, M. Nadeem, M. Atif, R. Grossinger, Metal–semiconductor transition in NiFe2O4 nanoparticles due to reverse cationic distribution by impedance spectroscopy, J. Appl. Phys. 109 (2011) 093704. [2] E. Senturk, Y. Koseoglu, T. Sasmaz, F. Alan, M. Tan, RC circuit and conductivity properties of Mn0.6Co0.4Fe2O4 nanocomposite synthesized by hydrothermal method, J. Alloy. Compd. 578 (2013) 90. [3] M. Jeun, S. Lee, Y.J. Kim, H.Y. Jo, K.H. Park, S.H. Paek, Y. Takemura, Physical parameters to enhance AC magnetically induced heating power of ferrite nanoparticles for hyperthermia in nanomedicine, IEEE Trans. Nanotechnol. 12 (2013) 314. [4] V.M. Khot, A.B. Salunkhe, N.D. Thorat, M.R. Phadatare, S.H. Pawar, Induction heating studies of combustion synthesized MgFe2O4 nanoparticles for hyperthermia applications, J. Magn. Magn. Mater. 332 (2013) 48. [5] Y. Huang, Y. Tang, J. Wang, Q. Chen, Synthesis of MgFe2O4 nanocrystallites under mild conditions, Mater. Chem. Phys. 97 (2006) 394. [6] S. Singhal, J. Singh, S.K. Barthwal, K. Chandra, Preparation and characterization of nanosize nickel-substituted cobalt ferrites (Co1 xNixFe2O4), J. Solid State Chem. 178 (2005) 3183. [7] P.C. Taylor, P.J. Bray, Computer simulations of magnetic resonance spectra observed in polycrystalline and glassy samples, J. Magn. Res. 2 (1970) 305. [8] D.L. Griscom, Ferromagnetic resonance of precipitated phases in natural glasses, J. Non-Cryst. Solids 67 (1984) 81. [9] R.S. de Biasi, R.D.S. Lopes, D.G. Carvalho, A.B.S. Figueiredo, FMR lineshape of cobalt ferrite nanoparticles, Ceram. Int. 41 (2015) 865. [10] B.D. Cullity, C.D. Graham, Introduction to Magnetic Materials, 2nd edition, Wiley, New York, 2009.
Contents lists available at ScienceDirect
Ceramics International journal homepage: www.elsevier.com/locate/ceramint
Short communication
Magnetocrystalline anisotropy of NiCoFe2O4 nanoparticles Ronaldo Sergio de Biasi a,b,n, Rayanne Dezio de Souza Lopes a,b a b
Departamento de Engenharia Mecânica e de Materiais, Instituto Militar de Engenharia, Praça General Tiburcio, 80, 22290-270 Rio de Janeiro, RJ, Brazil Seção de Engenharia Mecânica e de Materiais, Instituto Militar de Engenharia, 22290-270 Rio de Janeiro, RJ, Brazil
art ic l e i nf o
a b s t r a c t
Article history: Received 10 November 2015 Received in revised form 17 February 2016 Accepted 23 February 2016 Available online 24 February 2016
Nanosized particles of Ni1 xCoxFe2O4 were synthesized by the sol–gel combustion method and the physical properties of these mixed ferrites were studied by X-ray diffraction and ferromagnetic resonance. The average crystallite size in samples with different Ni–Co ratios was determined from the X-ray diffractograms, whereas ferromagnetic resonance spectra were used to study the dependence of the magnetocrystalline anisotropy on the relative concentration of nickel and cobalt. According to the X-ray diffractograms, the samples are single phase and the crystallite size is between 9 and 22 nm. The ferromagnetic resonance spectra showed that the magnetocrystalline anisotropy of the samples is positive, except for pure NiFe2O4, and increases monotonically with Co concentration, a result that could be of interest for practical applications. & 2016 Elsevier Ltd and Techna Group S.r.l. All rights reserved.
Keywords: A. Sol–gel processes C. Magnetic properties D. Ferrites
1. Introduction
2. Experimental procedure and results
Nanosized ferrites have important technological [1,2] and biomedical [3,4] uses. Mixed ferrites are a common approach to optimize the magnetic properties of the material for particular applications. Since the magnetocrystalline anisotropies of nickel ferrite and cobalt ferrite have opposite signs, one can adjust the magnetic anisotropy of nickel–cobalt ferrite over a wide range by changing the relative amounts of nickel and cobalt. In the present work, we made a series of samples of composition Ni1 xCoxFe2O4, using the sol–gel/combustion method [5], and determined the magnetocrystalline anisotropy of the material by ferromagnetic resonance. X-ray diffraction was used to estimate the average crystallite size. Although the saturation magnetization of this mixed ferrite has been previously studied by other researchers [6], this is the first time, to our knowledge, that the magnetocrystalline anisotropy of NiCoFe2O4 nanoparticles is investigated in a systematic way.
2.1. Sample preparation Stoichiometric amounts of analytical grade Fe(NO3)3 9H2O, Ni(NO3)2 6H2O and Co(NO3)2 6H2O were dissolved in deionized water to obtain the starting solution. To this was added a 0.75 M solution of citric acid (C6H8O7 H2O). The resulting solution was stirred for 4 h at 60 °C, heated to 80 °C and kept at this temperature until the sol turned into a transparent gel. The gel was then heated to 200 °C for 20 min so that auto-combustion would take place. 2.2. X-ray measurements X-ray diffractograms were recorded in a PANalytical X'Pert PRO diffractometer using Cu Kα radiation. The diffraction patterns of Ni1 xCoxFe2O4 samples, for x ¼0, 0.2, 0.4, 0.6, 0.8 and 1.0, are shown in Fig. 1. The patterns for x¼ 0 and x¼ 1 matched, respectively, the ICSD patterns 084677 (NiFe2O4) and 066759 (CoFe2O4). The average crystallite sizes shown in Table 1 are estimated using the Debye–Scherrer equation
d= n
Corresponding author at: Departamento de Engenharia Mecânica e de Materiais, Instituto Militar de Engenharia, Praça General Tiburcio, 80, 22290-270 Rio de Janeiro, RJ, Brazil. E-mail addresses: [email protected] (R.S. de Biasi), [email protected] (R.D. de Souza Lopes). http://dx.doi.org/10.1016/j.ceramint.2016.02.141 0272-8842/& 2016 Elsevier Ltd and Techna Group S.r.l. All rights reserved.
0. 9 λ B cos θ
(1)
where d is the average crystallite size, λ is the X-ray wavelength, B is the linewidth at half the line intensity and θ is the Bragg angle. We used for B the average value for the five most intense lines in the diffractograms, labeled in the bottom diffractogram of Fig. 1.
9316
R.S. de Biasi, R.D. de Souza Lopes / Ceramics International 42 (2016) 9315–9318
Fig. 1. X-ray diffraction patterns of Ni1 xCoxFe2O4 samples for several values of x.
Table 1 Average crystallite size of Ni1 xCoxFe2O4 samples. x
Composition
d (nm)
0.0 0.2 0.4 0.6 0.8 1.0
NiFe2O4 Ni0.8Co0.2Fe2O4 Ni0.6Co0.4Fe2O4 Ni0.4Co0.6Fe2O4 Ni0.2Co0.8Fe2O4 CoFe2O4
19 22 18 17 16 9
2.3. Ferromagnetic resonance measurements Ferromagnetic resonance measurements were performed at room temperature and 9.50 GHz using a Varian E-12 spectrometer with 100 kHz field modulation. The microwave power was 5 mW and the modulation amplitude was 1 mT. The magnetic field was calibrated with an NMR gaussmeter. The ferromagnetic resonance spectra of Ni1 xCoxFe2O4 samples are shown in Fig. 2(a)–(e) for x ¼0, 0.2, 0.4, 0.6, 0.8 and 1.0. The experimental results were fitted to theoretical spectra using a computer program developed by Taylor and Bray [7] for paramagnetic resonance spectra and adapted by Griscom [8] for ferromagnetic resonance spectra. The fitting was generally good, except for the low field part of the spectra, where the slope of the amplitude rise is much steeper in the experimental curves. This
mismatch is attributed [9] to superparamagnetic effects. The fitting parameters are shown in Table 3 and the dependence of the anisotropy field on cobalt concentration is shown in Fig. 3. The magnetocrystalline anisotropy of the samples was computed from the anisotropy field using equation [8]
K = 2πMs HA
(2)
where Ms is the saturation magnetization of the nanoparticles. The values of Ms were taken from the literature [6] and the values of HA were taken from Table 2; the results are shown in Table 3 and Fig. 4. Since [10] the anisotropy of bulk cobalt ferrite is large and positive ( þ2 105 J/m3) and the anisotropy of bulk nickel ferrite is small and negative ( 0.062 105 J/m3), it is expected that the anisotropy of Ni–Co ferrites be positive, except for small cobalt concentrations, and increase with increasing Co content.
R.S. de Biasi, R.D. de Souza Lopes / Ceramics International 42 (2016) 9315–9318
9317
Fig. 2. Ferromagnetic resonance spectra of samples of Ni1 xCoxFe2O4 for several values of x.
That is exactly what was found in the present work (see Table 3 and Fig. 4); the values of K range from 1.15 105 J/m3 for x ¼0.0 to þ2.25 105 J/m3 for x¼ 1.0. The fact that the absolute value of the anisotropy of nickel ferrite nanoparticles is much larger than that of its bulk counterpart may be attributed to a different cation distribution related to the preparation method, but this question should be investigated further using other experimental methods, such as Mössbauer spectroscopy.
3. Conclusions The physical properties of particles of the mixed ferrite Ni1 xCoxFe2O4 prepared by the sol–gel/combustion method were investigated using the X-ray diffraction and ferromagnetic resonance techniques. The X-ray results showed that the samples are single phase and that the crystallite size is in the nanometer range. The ferromagnetic resonance results showed that the magnetocrystalline
9318
R.S. de Biasi, R.D. de Souza Lopes / Ceramics International 42 (2016) 9315–9318
anisotropy of the samples increases monotonically with Co concentration, a result that could be of interest for practical applications.
Acknowledgments The authors thank CAPES and CNPq for financial support.
References
Fig. 3. Anisotropy field of Ni1 xCoxFe2O4 for several values of x. The lines are only guides to the eye. Table 2 Ferromagnetic resonance parameters of Ni1 xCoxFe2O4 samples. x
g-Factor
Anisotropy field (T)
Intrinsic linewidth (T)
0.0 0.2 0.4 0.6 0.8 1.0
2.10 2.10 2.10 2.10 2.10 2.10
0.0715 0.0400 0.0600 0.0752 0.0782 0.0800
0.2950 0.2690 0.2448 0.2100 0.1820 0.1800
Table 3 Parameters used in the calculation of the anisotropy constant of Ni1 xCoxFe2O4 samples. x
Density (g/ cm³)
MS (emu/g)
MS (A/m)
Anisotropy field (T)
Anisotropy constant (J/m3)
0 0.2 0.4 0.6 0.8 1.0
5.380 5.362 5.344 5.326 5.308 5.290
47.6 53.9 61.5 69.3 74.7 84.5
2.56 105 2.89 105 3.28 105 3.69 105 3.96 105 4.47 105
0.0715 0.0400 0.0600 0.0752 0.0782 0.0800
1.15 105 0.73 105 1.24 105 1.74 105 1.95 105 2.25 105
Fig. 4. Magnetocrystalline anisotropy of Ni1 xCoxFe2O4 for several values of x. The lines are only guides to the eye.
[1] M. Younas, M. Nadeem, M. Atif, R. Grossinger, Metal–semiconductor transition in NiFe2O4 nanoparticles due to reverse cationic distribution by impedance spectroscopy, J. Appl. Phys. 109 (2011) 093704. [2] E. Senturk, Y. Koseoglu, T. Sasmaz, F. Alan, M. Tan, RC circuit and conductivity properties of Mn0.6Co0.4Fe2O4 nanocomposite synthesized by hydrothermal method, J. Alloy. Compd. 578 (2013) 90. [3] M. Jeun, S. Lee, Y.J. Kim, H.Y. Jo, K.H. Park, S.H. Paek, Y. Takemura, Physical parameters to enhance AC magnetically induced heating power of ferrite nanoparticles for hyperthermia in nanomedicine, IEEE Trans. Nanotechnol. 12 (2013) 314. [4] V.M. Khot, A.B. Salunkhe, N.D. Thorat, M.R. Phadatare, S.H. Pawar, Induction heating studies of combustion synthesized MgFe2O4 nanoparticles for hyperthermia applications, J. Magn. Magn. Mater. 332 (2013) 48. [5] Y. Huang, Y. Tang, J. Wang, Q. Chen, Synthesis of MgFe2O4 nanocrystallites under mild conditions, Mater. Chem. Phys. 97 (2006) 394. [6] S. Singhal, J. Singh, S.K. Barthwal, K. Chandra, Preparation and characterization of nanosize nickel-substituted cobalt ferrites (Co1 xNixFe2O4), J. Solid State Chem. 178 (2005) 3183. [7] P.C. Taylor, P.J. Bray, Computer simulations of magnetic resonance spectra observed in polycrystalline and glassy samples, J. Magn. Res. 2 (1970) 305. [8] D.L. Griscom, Ferromagnetic resonance of precipitated phases in natural glasses, J. Non-Cryst. Solids 67 (1984) 81. [9] R.S. de Biasi, R.D.S. Lopes, D.G. Carvalho, A.B.S. Figueiredo, FMR lineshape of cobalt ferrite nanoparticles, Ceram. Int. 41 (2015) 865. [10] B.D. Cullity, C.D. Graham, Introduction to Magnetic Materials, 2nd edition, Wiley, New York, 2009.