Effect of zinc substitution on structural and magnetic properties of cobalt ferrite

Effect of zinc substitution on structural and magnetic properties of cobalt ferrite

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ProcediaProcedia Engineering 00 (2012) 000–000 Engineering 32 (2012) 597 – 602 www.elsevier.com/locate/procedia

I-SEEC2011

Effect of zinc substitution on structural and magnetic properties of cobalt ferrite A. Hassadeea*, T. Jutarosagaa,b, W. Onreabroya,b a

b

Department of Physics, Faculty of Science, King Mongkut’s University of Technology Thonburi, Bangkok, 10140, Thailand. Research Center in Thin Film Physics, Thailand Center of Excellence in Physics, 328 Si Ayutthaya Rd., Bangkok, 10400, Thailand. Elsevier use only: Received 30 September 2011; Revised 10 November 2011; Accepted 25 November 2011.

Abstract Zinc-substituted cobalt ferrites, Co1-xZnxFe2O4 (x = 0.0 – 0.5), were prepared by ceramic processing. The crystal structural, morphological and magnetic properties of the products were determined by X-ray diffractometry (XRD), scanning electron microscopy (SEM), and vibrating sample magnetometer (VSM) respectively. The results revealed that the spinel structure was also modified by the substitute ions. In Co1-xZnxFe2O4 samples, Zn2+ commonly substitute for Co2+, resulting in an increase in the lattice parameter from 8.381 – 8.412 Å. Magnetization measurements indicated that Co1-xZnxFe2O4 samples with x = 0.0 – 0.5 showed ferrimagnetic behavior at room temperature. The decrease in the maximum magnetization of the Co1-xZnxFe2O4 samples from 134 to 100 emu/g and the decrease in the coercivity of the Co1-xZnxFe2O4 samples from 140 to 4 Oe by increasing the zinc content from 0.0 to 0.5 can be attributed to the magnetic characteristic and the anisotropic nature of cobalt.

© 2010 Published by Elsevier Ltd. Selection and/or peer-review under responsibility of I-SEEC2011 Keywords: Magnetic properties; cobalt ferrites; Co1-xZnxFe2O4

1. Introduction The magnetic material is extremely important, because it is a widely used such as motor, electronic equipment and Hard Disk Drive (HDD), etc. The main component of ceramic magnets is iron (Fe). These magnets are divided into two types, hard ferrite and soft ferrite. The hard ferrite is suitable for implementation of high inductance, while the soft ferrite is suitable for the implementation of high frequency applications. Cobalt ferrite is known as one of the candidates for the recording media application due to the suitable coercivity (Hc), the saturation magnetization (Ms) and strong anisotropy. It

* Corresponding author. Tel.: +0-662-470-8876; fax: +0-662-427-8785. E-mail address: [email protected]

1877-7058 © 2012 Published by Elsevier Ltd. doi:10.1016/j.proeng.2012.01.1314

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had been shown in the earlier research that the magnetics properties of Co ferrite could be modified by the addition of other metal atoms. For example, Zhang et al. [1] showed that Ni addition into Co ferrite thin films suppressed the grain formation, resulting in the reduction of surface roughness. Also, by substitution of Zn2+ cation for Co2+ cation in the cobalt ferrite structure, many research groups has shown that the structural and magnetic properties can be modified such as the reduction of coercity and the increase of lattice constant as Zn concentration increased. To synthesize these kinds of materials, besides the vacuum technique, various methods such as co-precipitation [2, 3], microwave [4], sol-gel [5] and hydrolysis [6] could be used. Most reported methods were used to synthesize either thin films or nanoparticles. In our case, we were interested in fabricating solid sputtering target of Co1xZnxFe2O4 via ceramic method. Therefore, it is important to investigate the structural and magnetic properties of the fabricated Co1-xZnxFe2O4 (x = 0.0 to 0.5) target using precursors of CoO (Cobalt Oxide), ZnO (Zinc Oxide) and Fe2O3 (Iron (III) Oxide). 2. Experimental All ferrite samples were prepared using the standard ceramic process. The starting materials used in this study were ZnO (Sigma-Aldrich, 99.9%), CoO (Sigma-Aldrich), and Fe2O3 (Sigma-Aldrich, 99%) mixed together to form the composition of Co1-xZnxFe2O4. These materials were weighed in the composition of Co:Zn:Fe = 1-x : x : 2, where x varies from 0 to 0.5. Mixtures of these raw materials were milled in ethanol for 20 minutes. The mixed powder was dried, crushed, and sifted. The granules were calcined at 1100 °C for 2 hours. After calcining and sieving, the powders were pressed into a disk shape compacts. The green bodies were sintered in air at 1350°C for 2 hours. The crystalline phases of the powder and ceramic samples were studied by a X-ray diffractometer (XRD) using CuKα radiation, (XRD, Bruke, D8). The microstructure of the samples was investigated using a field emission scanning electron microscope (FESEM, Hitachi, S-4700). Grain sizes of the as-sintered samples were measured employing the intercept method. Magnetic measurements at room temperature were conducted using a vibrating sample magnetometer (VSM). All the hysteresis magnetic measurements were carried out at room temperature on the sintered samples in the applied static magnetic fields up to 7.3 kOe. 3. Result and discussion 3.1. X-ray diffraction analysis Fig. 1 shows the XRD patterns of the Co1-xZnxFe2O4 samples. As compared with JCPDS data, the patterns of all the compositions can be indexed as a pure cubic spinel structure, and clear evidence of secondary phases was not found. All XRD peaks are correspondent with the JCPDS file no. 82-1049 (ZnFe2O4) and 22-1086 (CoFe2O4). The small half width of each peak indicated the large crystallite size. Using the XRD data, the lattice constant for each peak of each sample was calculated by using the formula: a = d (h2 + k2 + l2)1/2, where h, k, and l are miller indices of the crystal planes. As shown in Fig. 2, the lattice parameter (a) increases from 8.381 to 8.412 Å with the increase in zinc content from 0.0 to 0.5. It is shown that the lattice parameter linearly increases with increasing Zn content, confirming that the larger Zn cations substituted for smaller Co cations in the Co ferrite structures. This trend is similar to the Co1-xZnxFe2O4 nanoparticles synthesized by the co-precipitation method [3].

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x = 0.0

 

x = 0.1

x = 0.3

x = 0.4

     

x=0.5 ZnFe 2 O 4 : 82-1049 CoFe 2 O 4 : 22-1086

20

30

40



50

60

70

Fig. 1. X-ray diffraction patterns of Co1-xZnxFe2O4 samples sintered at 1350oC with x varied from 0.0 to 0.5

Lattice parameter (Å)

 

x = 0.2

Intensity (a.u.)

       

   

8.42 8.41 8.40 8.39 8.38 8.37 8.36

0.0

0.1

0.2

0.3

0.4

0.5

Zn concentration (x) Fig. 2. Lattice parameter (a) of Co1-xZnxFe2O4 samples sintered at 1350oC with x varying from 0.0 to 0.5

3

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3.2. Field emission scanning electron microscope analysis The as-sintered bulk surface morphology of Co1-xZnxFe2O4 samples were investigated using field emission scanning electron microscopy (FESEM) and the results are shown in Fig. 3. It is shown grain size of Co1-xZnxFe2O4 samples with x varying from 0.0 to 0.5 when sintered at 1350°C for 2 hours were about 7 to 11 µm. X = 0.0

X = 0.1

10 μm X = 0.2

10 μm X = 0.3

10 μm X = 0.4

10 μm X = 0.5

10 μm

10 μm

Fig. 3. FESEM images of Co1-xZnxFe2O4 samples sintered at 1350oC with x varied from 0.0 to 0.5

3.3. Magnetic measurement After sintering, the Co1-xZnxFe2O4 ferrite showed required magnetic properties. It could easily be magnetized by an external field, exhibiting the well-known hysterresis effect. The magnetic property was investigated with a vibrating sample magnetometer (VSM) at room temperature. Magnetic measurement was investigated with a maximum magnetic field of 7.3 kOe. Using this magnetic field, the Ms could not be obtained. Therefore, we showed the maximum magnetization (Mm) instead. Fig. 4 shows the room temperature hysteresis loop of the Co1-xZnxFe2O4 samples over the field ranging from -7 kOe to 7 kOe for various zinc substitutions.

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Magnetization (M, emu/g)

150

5

x = 0.3 x = 0.0

100

x = 0.5

50 0 -50 -100 -150 -10000

-5000

0

5000

10000

Field (H, Oe) Fig. 4. Room temperature magnetization cures of Co1-xZnxFe2O4 samples sintered at 1350oC with x varied from 0.0 to 0.5 at maximum external magnetic field 7.3 kOe 150

Mm

150

100

100

50

50

0

0

Hc (Oe)

Mm (emu/g)

Hc

0.0

0.1

0.2

0.3

0.4

0.5

x

Fig. 5. Variation of maximum magnetization (Mm) and coercivity (Hc) of Co1-xZnxFe2O4 samples sintered at 1350°C with x varied from 0.0 to 0.5 at maximum external magnetic field 7.3 kOe

The value of magnetization sharply increases with the external magnetic field strength at low field region. It can be seen that the variation of Mm and Hc as a function of Zn content as shown in Fig. 5. The Mm increases with small substitutions and reaches the maximum value of 0.35 emu/g at 7.3 kOe for x = 0.3 and then decreases. The change in the coercivity with the degree of zinc substitution clearly decreased with Zn content (x). The low coercive force confirms that the cobalt-zinc ferrite is a soft ferrite. The difference in the Hc values is understandable because the Zn substantially increases inside the grain in response to the increase of unit cell volume.

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4. Conclusion Ferrites are ferrimagnetic oxides with dielectric and magnetic properties that are useful for radio frequency (RF) and microwave applications. Spinel ferrites typically have general formula of MeFe2O4. Me represents one or several of divalent transition metal such as Zn, Co, Mn, Ni, Cu, Mg, ZnCo, Ni-Zn-Co, etc. The results revealed that the spinel structure of Co1-xZnxFe2O4 was modified by the substitute ions. In Co1-xZnxFe2O4, Zn2+ commonly substituted for Co2+ in the crystal structure, resulting in an increase in the lattice parameter from 8.381 to 8.412 Å. Magnetization measurements indicated that Co1-xZnxFe2O4 samples with x = 0 – 0.5 showed ferrimagnetic behavior at room temperature. The decrease in the magnetization of the Co1-xZnxFe2O4 samples from 134 to 100 emu/g and the decrease in the coercivity of the Co1-xZnxFe2O4 samples from 140 to 4 Oe by increasing the zinc content from 0 to 0.5 can be attributed to the magnetic characteristic and the anisotropic nature of cobalt. Acknowledgments This work was supported by the Higher Education Research Promotion and National Research University Project of Thailand, Office of the Higher Education Commission. The author would like to thank Dr. Pongsakron Jantarattana, Department of Physics, Faculty of Science, Kasetsart University who provided the assistance in the VSM measurement. References [1] Zhang F, Kitamoto Y, Abe M, Naoe M, Effect of Ni addition into Co ferrite thin films for perpendicular recording media. Journal of Applied Physics 2000; 87: 6881-6883. [2] Vaidyanathan G, Sendhilnatha S. Characterization of Co1-xZnxFe2O4 nanoparticles synthesized by co-precipitation method. Physica B 2008; 403: 2157-2167. [3] Vaidyanathan G, Sendhilnathan S, Arulmurugan R. Structural and magnetic properties of Co1-xZnxFe2O4 nanoparticles by coprecipitation method. Journal of Magnetism and Magnetic Materials, 2007; 313: 293-299. [4] Köseoglu Y, Baykal A, Gözuak F. Structural and magnetic properties of CoxZn1-xFe2O4 nanocrystals synthesized by microwave method. Polyhedron 2009; 28: 2887-2892. [5] Duque S, Macêdo MA, Moreno NO, Lopez JL, Pfanes HD. Magnetic and structural properties of CoFe2O4 thin films synthesized via a sol-gel process. Journal of Magnetism and Magnetic Materials 2001; 226-230: 1424-1425. [6] Duong GV, Sato R, Hanh N, Linh DV, Reissner M, Michor H, Fidler J, Wiesinger G, Grössimger R. Magnetic properties of nanocrystalline Co1-xZnxFe2O4 prepared by forced hydrolysis method. Journal of Magnetism and Magnetic Materials 2006; 307: 313-317.