- Email: [email protected]
Synthesis and magneto-structural study of CoxFe3−xO4 nanoparticles
ARTICLE IN PRESS
Journal of Magnetism and Magnetic Materials 294 (2005) e33–e36 www.elsevier.com/locate/jmmm
Synthesis and magneto-structural study of CoxFe3xO4 nanoparticles R. Betancourt-Galindoa,b,, O. Ayala-Valenzuelab, L.A. Garcı´ a-Cerdaa, O. Rodrı´ guez Ferna´ndeza, J. Matutes-Aquinob, G. Ramosc, H. Yee-Madeirad a
Centro de Investigacio´n en Quı´mica Aplicada, Blvd. Enrique Reyna Hermosillo No. 140 CP 25000 Saltillo, Coahuila, Me´xico Centro de Investigacio´n en Materiales Avanzados, Miguel de Cervantes Saavedra. No. 120. Complejo Industrial Chihuahua, Chihuahua, Chih. Me´xico c Centro de Investigacio´n en Ciencia Aplicada y Tecnologı´a Avanzada, Jose´ Siurob No. 10. Col. Alameda, CP 76040 Quere´taro, Qro. Me´xico d Escuela Superior de Fisica y Matema´ticas, IPN, Edif. 9, U. Prof. ‘‘ALM’’, 07738 Col. Lindavista, Me´xico D.F., Me´xico
b
Available online 15 April 2005
Abstract The Co2+ ion in an octahedral site of the cubic spinel structure has a highly anisotropic character. The electric crystal field produces a degenerate ground state with a orbital magnetic momentum fixed parallel to a /1 1 1S trigonal axis, and the spin–orbit interaction tends to align the spin magnetic moment parallel to this trigonal axis giving high anisotropy. Then, the use of CoxFe3xO4 system allows the tailoring of the magnetic properties by changing the cobalt content, which can be very useful in magnetic fluids, magnetic latex and free rotors applications. In this work CoxFe3xO4 nanoparticles over a compositional range 0:0oxo1:0 were synthesized by chemical co-precipitation from iron and cobalt salts using ammonium hydroxide as precipitating agent. The powders were characterized by X-ray diffraction, transmission electronic microscopy and vibrating sample magnetometry. Nanoparticles with a size smaller than 15 nm with a narrow particle distribution size were obtained. X-ray diffraction confirmed the formation of a unique phase. The magnetic behavior of CoxFe3xO4 powders shows that an increase of the cobalt contain yields a steadily decrease in the maximum magnetization. r 2005 Elsevier B.V. All rights reserved. PACS: 75.75+a; 76.80+y Keywords: Chemical co-precipitation; Nanoparticles; Superparamagnetism; Mo¨ssbauer effect
Corresponding author. Centro de Investigacio´n en Quı´ mica Aplicada, Blvd. Enrique Reyna Hermosillo No. 140 CP 25000 Saltillo,
Coahuila, Me´xico. Tel.: +52 844 4389830x1377; fax: +52 844 4389839. E-mail address: [email protected] (R. Betancourt-Galindo). 0304-8853/$ - see front matter r 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.jmmm.2005.03.049
ARTICLE IN PRESS e34
R. Betancourt-Galindo et al. / Journal of Magnetism and Magnetic Materials 294 (2005) e33–e36
1. Introduction Magnetic nanoparticles of the spinel-type receive much attention because of their interesting magnetic properties and potential applications [1]. It has been observed that they have superparamagnetic properties, due to its reduced size. This make them attractive candidates for information storage and many other applications including magnetic fluids, magnetic latex. They can be prepared using different methods like sol–gel [2], microemulsion [3], mechanical alloying [4] and chemical co-precipitation [5]. While techniques like microemulsion promise easy control over the particle size other techniques produce larger particles due to agglomeration during the different process steps. In this work, we report the study on the size distribution and properties of CoxFe3xO4 nanoparticles prepared using chemical co-precipitation.
with a 25 mCi Co57 (Rh) source in constant velocity mode at room temperature. The spectrometer was calibrated using in a-Fe standard prior to measurement. The morphology and particle size were characterized using a TEM JEOL 1200 EXII.
3. Results and discussion Fig. 1 shows the X-ray diffraction patterns of the CoxFe3xO4 powders with x ¼ 0.0, 0.2, 0.4, 0.8 and 1.0, where between six and seven broad diffraction peaks can be clearly observed in each pattern in good agreement with the diffraction peaks of CoFe2O4 small nanoparticles. Also a low angle amorphous halo that increases with x is observed. Fig. 2 shows a micrograph of the CoxFe3xO4 nanometric sized particles with x ¼ 0:2 obtained with TEM. The images for the other samples look
2. Experimental As starting materials iron and cobalt chlorides (FeCl3 6H2O, FeCl2 4H2O, CoCl2 6H2O) and NH4OH reagent grade were used. The CoxFe3xO4 nanoparticle precipitates were obtained from two starting solutions, one with a mixture of metallic salts with the proper stoichiometric proportion, and the other containing the alkali hydroxide. The chemical reaction was carried out using a molar ratio of 1:2 of Fe+2Co+2:Fe+3, at 70 1C under intense agitation. The alkali solution was added as fast as possible in order to keep a high pH level. No surfactants were used in our process. The precipitates were then thoroughly washed with distilled water to eliminate chloride ions and finally dried at room temperature for use. The precipitates were structurally characterized using a Siemens D5000 X-ray diffractometer. The magnetic characterization was carried out by means of magnetometry and Mo¨ssbauer spectrometry. The hysteresis curves were obtained using a Lakeshore 7300 vibrating sample magnetometer and a maximum field of 15000 Oe was used. The Mo¨ssbauer spectra were obtained in transmittance using a Wissel Scientific Instruments spectrometer
Fig. 1. X-ray diffraction patterns of CoxFe3xO4 samples.
ARTICLE IN PRESS R. Betancourt-Galindo et al. / Journal of Magnetism and Magnetic Materials 294 (2005) e33–e36
e35
Table 1 Maximum magnetization (Ms) and mean particle size (DP) of the different samples Composition
Ms (emu/g)
Dp (nm)
0 0.2 0.4 0.8 1
65.72 53.65 44.09 6.69 2.29
11 10.4 9.6 9.4 9
Fig. 2. TEM micrograph of Co0.2Fe0.8O4 sample.
Fig. 4. Magnetization curves of CoxFe3xO4 samples.
Fig. 3. Particle size distribution for the Co0.2Fe0.8O4 sample, obtained from TEM micrographs.
similar. Using TEM micrographs the particle size distribution histograms were calculated as shown in Fig. 3 for a typical sample. Particle sizes between 6 and 13 nm are observed, with a mean size of 10.4 nm. Again, the size distribution in all the samples was similar. Table 1 summarized these results. These sizes are in good agreement with sizes of similar particles obtained by other
researchers [6]. The particles showed a spherical morphology. Fig. 4 shows reversible magnetization curves, corresponding to the different CoxFe3xO4 compositions, with coercitivity and remanent magnetization values close to zero typical for a superparamagnetic behavior. With increasing cobalt content the maximum magnetization decreases steadily, but in the cases of samples with composition x ¼ 0:8 and 1.0 too low magnetization values can be observed due to an increasing non-magnetic amorphous residue from the precipitation process, which is confirmed by the X-ray patterns. Table 1 summarizes the saturation magnetization and mean particle size. The mean particle sizes
ARTICLE IN PRESS e36
R. Betancourt-Galindo et al. / Journal of Magnetism and Magnetic Materials 294 (2005) e33–e36 Table 2 Mo¨ssbauer spectra parameters for two selected samples (x ¼ 0:2, 0.8) Sample Co0.2Fe2.8O4
Co0.8Fe2.6O4
Site A Site B Doublet Site A Site B Doublet
H (kOe)
Qs (mm/s)
Is (mm/s)
473 437
0.057 0.08 0.73 0.05 0.04 0.66
0.28 0.28 0.36 0.29 0.32 0.39
472 435
4. Conclusions
Fig. 5. Mo¨ssbauer spectra for two selected samples x ¼ 0:2 and x ¼ 0:8 recorded at room temperature.
are very similar for different compositions. This is in contrast with the microemulsion technique, where the cobalt content apparently influences the size of the obtained particles [6]. Fig. 5 shows the Mo¨ssbauer spectra for x ¼ 0:2 and x ¼ 0:8 at room temperature displaying the experimental data (points) and the calculated background and spectral components (solid lines). Both spectra consist of a central superparamagnetic doublet and a sextet with broad lines due to size and anisotropy distributions in the particles system. Because the anisotropy increases with the cobalt content and the mean particle sizes are similar, the doublet intensity diminishes with the increase of the cobalt content. The deconvolution of the sextet with broad lines shows two sextets with similar hyperfine fields that are correlated with the A and B positions in the crystal lattice. The values of the hyperfine fields were similar in both samples, i.e. 47.3 and 47.2 T for the A site and 43.7 and 43.5 T for the B site, for x ¼ 0:2 and x ¼ 0:8, respectively (Table 2). The values of the Isomer shift are 0.36 and 0.39 mm/s for x ¼ 0:2 and x ¼ 0:8, respectively, while the Quadruple splitting values are 0.73 and 0.66 mm/s for x ¼ 0:2 and x ¼ 0:8, respectively (Table 2).
Nanoparticles of CoxFe3xO4 with spherical morphology were obtained with size distributions between 6 and 13 nm, with mean particle size around 9.4 nm for all the compositions studied, demonstrating the processing of nanometric particles with controlled size. Reversible magnetization curves demonstrate the superparamagnetic behavior in all compositions. Mo¨ssbauer spectra show two different particle fractions behaving ferrimagnetically and superparamagnetically, respectively. The similar mean particle sizes and the evolution of the superparamagnetic doublet intensity with cobalt content demonstrate that anisotropy increases with cobalt content.
Acknowledgements R. Betancourt-Galindo thanks to CONACyT— Me´xico for the financial support (scholarship 68250).
References [1] X. Li, C. Kutal, J. Magn.Magn. Mater. 134 (1994) 249. [2] J.G. Lee, J.Y. Park, C.S. Kim, J. Mater. Sci. 33 (1998) 3965. [3] M.L. Quintela, J. Rivas, J. Colloid Interface Sci. 158 (1993) 446. [4] Y. Zhu, Q. Wu, J. Nanoparticles Res. 1 (1999) 393. [5] T. Pannaparayil, S. Komarneni, IEEE Trans. Magn. 25 (1989) 4233. [6] X. Li, C. Kutal, J. Alloys Compd. 349 (2003) 264.
Journal of Magnetism and Magnetic Materials 294 (2005) e33–e36 www.elsevier.com/locate/jmmm
Synthesis and magneto-structural study of CoxFe3xO4 nanoparticles R. Betancourt-Galindoa,b,, O. Ayala-Valenzuelab, L.A. Garcı´ a-Cerdaa, O. Rodrı´ guez Ferna´ndeza, J. Matutes-Aquinob, G. Ramosc, H. Yee-Madeirad a
Centro de Investigacio´n en Quı´mica Aplicada, Blvd. Enrique Reyna Hermosillo No. 140 CP 25000 Saltillo, Coahuila, Me´xico Centro de Investigacio´n en Materiales Avanzados, Miguel de Cervantes Saavedra. No. 120. Complejo Industrial Chihuahua, Chihuahua, Chih. Me´xico c Centro de Investigacio´n en Ciencia Aplicada y Tecnologı´a Avanzada, Jose´ Siurob No. 10. Col. Alameda, CP 76040 Quere´taro, Qro. Me´xico d Escuela Superior de Fisica y Matema´ticas, IPN, Edif. 9, U. Prof. ‘‘ALM’’, 07738 Col. Lindavista, Me´xico D.F., Me´xico
b
Available online 15 April 2005
Abstract The Co2+ ion in an octahedral site of the cubic spinel structure has a highly anisotropic character. The electric crystal field produces a degenerate ground state with a orbital magnetic momentum fixed parallel to a /1 1 1S trigonal axis, and the spin–orbit interaction tends to align the spin magnetic moment parallel to this trigonal axis giving high anisotropy. Then, the use of CoxFe3xO4 system allows the tailoring of the magnetic properties by changing the cobalt content, which can be very useful in magnetic fluids, magnetic latex and free rotors applications. In this work CoxFe3xO4 nanoparticles over a compositional range 0:0oxo1:0 were synthesized by chemical co-precipitation from iron and cobalt salts using ammonium hydroxide as precipitating agent. The powders were characterized by X-ray diffraction, transmission electronic microscopy and vibrating sample magnetometry. Nanoparticles with a size smaller than 15 nm with a narrow particle distribution size were obtained. X-ray diffraction confirmed the formation of a unique phase. The magnetic behavior of CoxFe3xO4 powders shows that an increase of the cobalt contain yields a steadily decrease in the maximum magnetization. r 2005 Elsevier B.V. All rights reserved. PACS: 75.75+a; 76.80+y Keywords: Chemical co-precipitation; Nanoparticles; Superparamagnetism; Mo¨ssbauer effect
Corresponding author. Centro de Investigacio´n en Quı´ mica Aplicada, Blvd. Enrique Reyna Hermosillo No. 140 CP 25000 Saltillo,
Coahuila, Me´xico. Tel.: +52 844 4389830x1377; fax: +52 844 4389839. E-mail address: [email protected] (R. Betancourt-Galindo). 0304-8853/$ - see front matter r 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.jmmm.2005.03.049
ARTICLE IN PRESS e34
R. Betancourt-Galindo et al. / Journal of Magnetism and Magnetic Materials 294 (2005) e33–e36
1. Introduction Magnetic nanoparticles of the spinel-type receive much attention because of their interesting magnetic properties and potential applications [1]. It has been observed that they have superparamagnetic properties, due to its reduced size. This make them attractive candidates for information storage and many other applications including magnetic fluids, magnetic latex. They can be prepared using different methods like sol–gel [2], microemulsion [3], mechanical alloying [4] and chemical co-precipitation [5]. While techniques like microemulsion promise easy control over the particle size other techniques produce larger particles due to agglomeration during the different process steps. In this work, we report the study on the size distribution and properties of CoxFe3xO4 nanoparticles prepared using chemical co-precipitation.
with a 25 mCi Co57 (Rh) source in constant velocity mode at room temperature. The spectrometer was calibrated using in a-Fe standard prior to measurement. The morphology and particle size were characterized using a TEM JEOL 1200 EXII.
3. Results and discussion Fig. 1 shows the X-ray diffraction patterns of the CoxFe3xO4 powders with x ¼ 0.0, 0.2, 0.4, 0.8 and 1.0, where between six and seven broad diffraction peaks can be clearly observed in each pattern in good agreement with the diffraction peaks of CoFe2O4 small nanoparticles. Also a low angle amorphous halo that increases with x is observed. Fig. 2 shows a micrograph of the CoxFe3xO4 nanometric sized particles with x ¼ 0:2 obtained with TEM. The images for the other samples look
2. Experimental As starting materials iron and cobalt chlorides (FeCl3 6H2O, FeCl2 4H2O, CoCl2 6H2O) and NH4OH reagent grade were used. The CoxFe3xO4 nanoparticle precipitates were obtained from two starting solutions, one with a mixture of metallic salts with the proper stoichiometric proportion, and the other containing the alkali hydroxide. The chemical reaction was carried out using a molar ratio of 1:2 of Fe+2Co+2:Fe+3, at 70 1C under intense agitation. The alkali solution was added as fast as possible in order to keep a high pH level. No surfactants were used in our process. The precipitates were then thoroughly washed with distilled water to eliminate chloride ions and finally dried at room temperature for use. The precipitates were structurally characterized using a Siemens D5000 X-ray diffractometer. The magnetic characterization was carried out by means of magnetometry and Mo¨ssbauer spectrometry. The hysteresis curves were obtained using a Lakeshore 7300 vibrating sample magnetometer and a maximum field of 15000 Oe was used. The Mo¨ssbauer spectra were obtained in transmittance using a Wissel Scientific Instruments spectrometer
Fig. 1. X-ray diffraction patterns of CoxFe3xO4 samples.
ARTICLE IN PRESS R. Betancourt-Galindo et al. / Journal of Magnetism and Magnetic Materials 294 (2005) e33–e36
e35
Table 1 Maximum magnetization (Ms) and mean particle size (DP) of the different samples Composition
Ms (emu/g)
Dp (nm)
0 0.2 0.4 0.8 1
65.72 53.65 44.09 6.69 2.29
11 10.4 9.6 9.4 9
Fig. 2. TEM micrograph of Co0.2Fe0.8O4 sample.
Fig. 4. Magnetization curves of CoxFe3xO4 samples.
Fig. 3. Particle size distribution for the Co0.2Fe0.8O4 sample, obtained from TEM micrographs.
similar. Using TEM micrographs the particle size distribution histograms were calculated as shown in Fig. 3 for a typical sample. Particle sizes between 6 and 13 nm are observed, with a mean size of 10.4 nm. Again, the size distribution in all the samples was similar. Table 1 summarized these results. These sizes are in good agreement with sizes of similar particles obtained by other
researchers [6]. The particles showed a spherical morphology. Fig. 4 shows reversible magnetization curves, corresponding to the different CoxFe3xO4 compositions, with coercitivity and remanent magnetization values close to zero typical for a superparamagnetic behavior. With increasing cobalt content the maximum magnetization decreases steadily, but in the cases of samples with composition x ¼ 0:8 and 1.0 too low magnetization values can be observed due to an increasing non-magnetic amorphous residue from the precipitation process, which is confirmed by the X-ray patterns. Table 1 summarizes the saturation magnetization and mean particle size. The mean particle sizes
ARTICLE IN PRESS e36
R. Betancourt-Galindo et al. / Journal of Magnetism and Magnetic Materials 294 (2005) e33–e36 Table 2 Mo¨ssbauer spectra parameters for two selected samples (x ¼ 0:2, 0.8) Sample Co0.2Fe2.8O4
Co0.8Fe2.6O4
Site A Site B Doublet Site A Site B Doublet
H (kOe)
Qs (mm/s)
Is (mm/s)
473 437
0.057 0.08 0.73 0.05 0.04 0.66
0.28 0.28 0.36 0.29 0.32 0.39
472 435
4. Conclusions
Fig. 5. Mo¨ssbauer spectra for two selected samples x ¼ 0:2 and x ¼ 0:8 recorded at room temperature.
are very similar for different compositions. This is in contrast with the microemulsion technique, where the cobalt content apparently influences the size of the obtained particles [6]. Fig. 5 shows the Mo¨ssbauer spectra for x ¼ 0:2 and x ¼ 0:8 at room temperature displaying the experimental data (points) and the calculated background and spectral components (solid lines). Both spectra consist of a central superparamagnetic doublet and a sextet with broad lines due to size and anisotropy distributions in the particles system. Because the anisotropy increases with the cobalt content and the mean particle sizes are similar, the doublet intensity diminishes with the increase of the cobalt content. The deconvolution of the sextet with broad lines shows two sextets with similar hyperfine fields that are correlated with the A and B positions in the crystal lattice. The values of the hyperfine fields were similar in both samples, i.e. 47.3 and 47.2 T for the A site and 43.7 and 43.5 T for the B site, for x ¼ 0:2 and x ¼ 0:8, respectively (Table 2). The values of the Isomer shift are 0.36 and 0.39 mm/s for x ¼ 0:2 and x ¼ 0:8, respectively, while the Quadruple splitting values are 0.73 and 0.66 mm/s for x ¼ 0:2 and x ¼ 0:8, respectively (Table 2).
Nanoparticles of CoxFe3xO4 with spherical morphology were obtained with size distributions between 6 and 13 nm, with mean particle size around 9.4 nm for all the compositions studied, demonstrating the processing of nanometric particles with controlled size. Reversible magnetization curves demonstrate the superparamagnetic behavior in all compositions. Mo¨ssbauer spectra show two different particle fractions behaving ferrimagnetically and superparamagnetically, respectively. The similar mean particle sizes and the evolution of the superparamagnetic doublet intensity with cobalt content demonstrate that anisotropy increases with cobalt content.
Acknowledgements R. Betancourt-Galindo thanks to CONACyT— Me´xico for the financial support (scholarship 68250).
References [1] X. Li, C. Kutal, J. Magn.Magn. Mater. 134 (1994) 249. [2] J.G. Lee, J.Y. Park, C.S. Kim, J. Mater. Sci. 33 (1998) 3965. [3] M.L. Quintela, J. Rivas, J. Colloid Interface Sci. 158 (1993) 446. [4] Y. Zhu, Q. Wu, J. Nanoparticles Res. 1 (1999) 393. [5] T. Pannaparayil, S. Komarneni, IEEE Trans. Magn. 25 (1989) 4233. [6] X. Li, C. Kutal, J. Alloys Compd. 349 (2003) 264.