Hydrothermal synthesis and characterization of Mn1−xZnxFe2O4 nanoparticles

ARTICLE IN PRESS

Physica B 394 (2007) 100–103 www.elsevier.com/locate/physb

Hydrothermal synthesis and characterization of Mn1xZnxFe2O4 nanoparticles Jing Feng, Li-Qin Guo, Xiaodong Xu, Shu-Yan Qi, Mi-Lin Zhang College of Material Science and Chemistry Engineering, Harbin Engineering University, Harbin 150001, PR China Received 10 November 2006; received in revised form 9 February 2007; accepted 9 February 2007

Abstract Mn1xZnxFe2O4 nanoparticles were prepared by hydrothermal synthesis at 200 1C for 12 h and characterized by X-ray powder diffraction (XRD), FESEM and vibrating sample magnetometer (VSM) techniques. The additions of Zn2+ ions content reduced the nanoparticles size. With the increase of Zn2+ ions content, the Curie temperature (Tc) increased firstly and then decreased; when x ¼ 0.3 the Tc reaches the maximum value (430 K). The results could be explained that the Zn2+ ions changed spin ordering to increase the Tc in the range of xp0.3, and magnetic properties were decreased because of increase of nonmagnetic Zn2+ ions in the range of x40.3. r 2007 Elsevier B.V. All rights reserved. PACS: 75.50.K Keywords: Hydrothermal; ZnMn ferrites; Curie temperature

1. Introduction Mn1xZnxFe2O4 possesses a spinel structure, in which Mn2+, Zn2+ and Fe3+ cations are distributed among tetrahedral and octahedral sites. In general, the spinel are classified as normal, inverse and mixed. In most cases, Mn2+ ions tend to be the octahedral sites and produce an inverse spinel structure. Zn2+ ions prefer to hold the tetrahedral positions which result in a normal spinel structure. The Mn1xZnxFe2O4 have mixed structure, and the magnetic properties of MnZn ferrites are dependent on their chemical composition, grain size, etc. [1]. Due to these special structures, MnZn ferrite particles have been intensively investigated for various applications such as transformers [2], electromagnetic interference [3], asymmetric digital subscriber line [4], etc. Otherwise, the processing technique has been seen a sensitive factor [5] for the magnetic properties of MnZn ferrite. The MnZn ferrite particles can be prepared using various Corresponding author. Tel.: +86 451 82589696; fax: +86 451 82533026. E-mail address: [email protected] (J. Feng).

0921-4526/$ - see front matter r 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.physb.2007.02.015

preparation techniques such as high-energy ball milling [6], microemulsion [7], sol–gel [8], co-precipitation [9] and other chemical methods [10]. In these methods, hydrothermal synthesis has attracted great interest since it is a promising route to produce highly crystallized structures having a narrow size distribution. In addition, hydrothermal synthesis could control the morphology of samples [11]. For magnetic materials, which are used at room temperature, their Curie temperature (Tc) is an important characteristic which will affect their application. Whereas, many reports are focus on the Ms changing, the Tc changes with doping is few studied. Arulmurugan et al. [12,13] found Curie temperature decreased with the increase in Zn2+ ions substitution in Mn(1x)ZnxFe2O4. Slama et al. [14] reported that Tc increased with Be and Cu concentration in (Ni0.3Zn0.7)1xMexFe2O4. To our knowledge, there is little information available in literature about a turning point of Curie temperature with the increase of Zn2+ ions content in the MnZn ferrites as reported in present paper. We synthesize Mn1xZnxFe2O4 nanoparticles with x varying from 0 to 1 using hydrothermal technique in this paper. The structure, morphology and

ARTICLE IN PRESS J. Feng et al. / Physica B 394 (2007) 100–103

2.1. Synthesis of Mn1xZnxFe2O4 nanoparticles The chemical reagents used in the work are sodium hydroxide, ferric chloride, manganese chloride and zinc chloride. All the reagents were of analytical grade and were not purified further before using. The Mn1xZnxFe2O4 powders with x varying from 0 to 1 were elaborated by using a hydrothermal route: a precursor solution was prepared by aqueous dissolution of mix chlorate sources and sodium hydroxide under stirring for about 20 min and pH is adjusted with ammonia. The mixed solution was poured into a Teflon lined stainless-steel autoclave with a filling degree of 80%. After heating at 200 1C for 12 h, the autoclave was cooled to room temperature naturally. The products were obtained by washing several times with hot de-ionized water and absolute ethanol and finally dried in a vacuum oven at 90 1C for 5 h. 2.2. Characterization X-ray powder diffraction (XRD) patterns were recorded on Rigaku D/MAX-rA diffractometer using Cu Ka radiation (l ¼ 1.54178 A˚). The diffractograms were obtained in the 2y range of 20–851. The morphologies of the samples were observed by FESEM (MX2600FE microscope, Camscan Britain), and the mean particle size was calculated with Debye-Scherrer’s equation from the fullwidth at half-maximum (FWHM) of the XRD pattern for the (3 1 1) plane of the spinel structure. The magnetic properties of Mn1xZnxFe2O4 powders were investigated by a vibrating sample magnetometer (VSM JDM-14D Jilin Changchun). 3. Results and discussion 3.1. XRD patterns Fig. 1 shows the XRD patterns of the samples. All diffraction peaks match well with the normal characteristic diffraction of MnFe2O4 (JCPDF file no. 10-0319). The result of analyzing X-ray diffraction patterns shows that the nominal composition structure with different Zn2+ ions content is single phase with cubic structure in which no additional lines correspond to any other phases. The XRD patterns give a clear evidence of transformation between ZnFe2O4 and MnFe2O4. One can see that the reflection peaks become sharper and stronger with decreasing x, which indicates the crystalloid growth. It is observed that the FWHM of (3 1 1) broadens monotonously, which indicates that the grain size of Mn1xZnxFe2O4 got smaller with increasing x. And average particle size from 50 nm for MnFe2O4 to 15 nm

Intensity / (a.u.)

(440)

(533)

x=1

(511)

(422)

(400)

2. Experimental

(311)

(220)

magnetic properties of Mn1xZnxFe2O4 nanoparticles have been studied.

101

x=0.6

x=0.3

x=0

20

30

40

50

60

70

80

2θ/ (°) Fig. 1. The XRD patterns of the Mn1xZnxFe2O4 system.

for ZnFe2O4 calculated by Debye-Scherrer formula from the (3 1 1) peak of XRD patterns. 3.2. FESEM image Fig. 2 shows the FESEM images of Mn1xZnxFe2O4 nanoparticles with different x. In Fig. 2(a) (x ¼ 0), it can be seen that the sample is composed of nanorod-like structures and nanoparticles. The nanorods are about 60 nm in diameter and 500 nm in length approximately and the nanoparticles is about 60 nm. The size of Fig. 2(b) (x ¼ 0.3) is smaller than the size at x ¼ 0. In addition, the smaller nanoparticles were observed in Fig. 2(c) (x ¼ 1). Meanwhile agglomeration phenomena occurred in Fig. 2(c) (x ¼ 1). It is found that the addition of Zn2+ ions contributes to decrease in the nanoparticles size, which is consistent with the report of Wang [13]. This phenomenon can be explained by the follow reasons: the radius of Mn2+ ions (0.93 A˚) is larger than that of Zn2+ ions (0.74 A˚), when the Mn2+ ions is replaced by Zn2+ ions at the A site, the lattice parameters become smaller with increase of x, so the size of nanoparticles decreases [15]. On the other hand, the surface energy of nanoparticles may be increased with the addition of Zn2+ ions content. 3.3. Magnetic properties The curves of the magnetization dependence of temperature for Mn1xZnxFe2O4 measured at 500 Oe are plotted in Fig. 3(a) and (b), which shows the curves of Curie temperature (Tc) dependence on x. As we know, Tc is the critical temperature transition from ferromagnetism to paramagnetism, which is determined by the maximum of dM/dT in M–T curve. It is obvious that the Tc of Mn1xZnxFe2O4 system increases with increase in Zn2+

ARTICLE IN PRESS 102

J. Feng et al. / Physica B 394 (2007) 100–103

x=0

2.0

M / (e mu/g)

x=1 1.5

x=0.6

x=0.3

1.0

0.5

240

280

320

360

400

440

Temperature / ( K )

440

Curie temperature / (K)

420 400 380 360 340 320 300 0.0

0.2

0.4

0.6

0.8

1.0

x Fig. 3. (a) Magnetization depends on temperature of Mn1xZnxFe2O4 and (b) Curie temperature (Tc) depends on x of Mn1xZnxFe2O4.

Fig. 2. The FESEM micrographs of Mn1xZnxFe2O4 system: (a) x ¼ 0, (b) x ¼ 0.3 and (c) x ¼ 1.

ions content from 0 to 0.3 and then decreases; the maximum is reached at the Zn2+ ions content of 0.3. The hystersis loops of samples measured at room temperature in Fig. 4 show obvious difference as Zn concentration changes. It can be seen that the Ms of this series samples shows the same trend as Tc. The Ms increases in the range

of xo0.3, and then decreases. The x ¼ 1 sample Mn1x ZnxFe2O4 shows paramagnetism at room temperature. From Fig. 3, we can see that the Curie temperature of MnFe2O4 is 413 K; this result is lower than the values in the literature reported [16]. Also, the Curie temperature of ZnFe2O4 is 306 K, which is bigger than the values reported by Tung et al. [17]. From the above results, we could conclude that the Tc is influenced by the preparation method and some other factors. The Tc and Ms increase in the range of xp0.3 which can be explained form the fact that the grain size becomes more uniform. This can help Zn2+ ions change spin ordering from Yafet-Kittel to Neel type. Since the energy required in offsetting the antiparallel spin alignment in Neel type is more than that required in Y-K type order, it results in an increase in Tc [18]. The reason of decreasing Tc in the range of x40.3 may be that Zn2+ ions are obviously nonmagnetic ions. The A–B site interaction is weakened with

ARTICLE IN PRESS J. Feng et al. / Physica B 394 (2007) 100–103

Zn2+ ions content increased, the average size of Mn1xZnxFe2O4 nanoparticles decreased and the agglomeration phenomena occurred at x ¼ 1. The Tc increased with Zn2+ ions content and reached a maximum value at x ¼ 0.3, then dropped steadily.

100 x=0 x=0.3 x=0.6 x=1.0

80 60

M (emu/g)

40

103

20

Acknowledgments

0 -20

We appreciate the financial support of the Doctor Subject Special Item Fund of Education Ministry (no. 20050217019) and Basic Research Fund of Harbin Engineering University (no. HEUFT05019).

-40 -60 -80 -100 -10000

-5000

0

5000

10000

H (Oe)

Fig. 4. Magnetic hysteresis curves measured at room temperature for Mn1xZnxFe2O4.

the increase of nonmagnetic Zn2+ ions, which induce Tc decrease. Another factor which contributes to decrease in Tc may lie in the variation in the lattice, defects and surface effects due to the small particle size or variations in the moments on the divalent ion sites as the Zn2+ ions content increases [19,20]. Our results are different from other reports [14], in which Tc increased with doping ions (Cu and Be) gradually. While there is a turning point in this report, this perhaps is induced by the different doping ionic trend to occupy different locations. In Arulmurugan et al. [12,13] reports, the Tc decrease with the increase in zinc substitution in Zn1xMnxFe2O4 synthesized by chemical co-precipitation method. In our work, all the curves of M–T have steep drop at Tc, while in the references all the M–T curves showed gentle drop. The difference with our results can be attributed to different synthesis method. Therefore, the processing technique is a sensitive factor for the magnetic properties of MnZn ferrite [5]. 4. Conclusion The hydrothermal process was employed to produce single-phase crystalline Mn1xZnxFe2O4 nanoparticles. Through the analysis of FESEM, it was shown that nanorods and nanoparticles were obtained at x ¼ 0. As

References [1] A.C.F.M. Costa, E. Tortella, M.R. Morelli, R.H.G.A. Kiminami, J. Magn. Magn. Mater. 256 (2003) 174. [2] K.I. Arshak, A. Ajina, D. Egan, Microelectron. J. 32 (2001) 113. [3] J.-H. Lee, M. Martin, H.-I. Yoo, J. Phys. Chem. Sol. 61 (2000) 1597. [4] G. Ott, J. Wrba, R. Lucke, J. Magn. Magn. Mater 254–255 (2003) 535. [5] A. Verma, T.C. Goel, R.G. Mediratta, in: Second International Conference on Processing Materials for Properties, The Mineral, Metal & Material Society, 2000, p. 493. [6] B. Sko"yszewska, W. Tokarz, K. Przybylski, Z. Kakol, Physica C 387 (2003) 290. [7] A. Kosak, D. Makovec, A. Znidarsic, M. Drofenik, J. Eur. Ceram. Soc. 24 (2004) 959. [8] K. Mandal, S.P. Mandal, P. Agudo, M. Pal, Appl. Surf. Sci. 82 (2001) 386. [9] B. Jeyadevan, C.N. Chinnasamy, K. Shinoda, K. Tohji, J. Appl. Phys. 93 (2003) 8450. [10] R. Justin Joseyphus, A. Narayanasamy, K. Shinoda, B. Jeyadevan, K. Tohji, J. Phys. Chem. Sol. 67 (2006) 1510. [11] J. Wang, C. Zeng, Z.M. Peng, Q.W. Chen, Physica B 349 (2004) 124. [12] R. Arulmurugan, B. Jeyadevan, G. Vaidyanathan, S. Sendhilnathan, J. Magn. Magn. Mater. 288 (2005) 470. [13] R. Arulmurugan, G. Vaidyanathan, S. Sendhilnathan, B. Jeyadevan, J. Magn. Magn. Mater. 298 (2006) 83. [14] J. Slama, R. Sosoudil, M. Usakova, E. Usak, A. Gruskova, V. Jancarik, J. Magn. Magn. Mater. 304 (2006) e758. [15] X.Y. Guo, X.R. Yan, X.L. Cui, J.P. Wang, T. Bai, J. Inorg. Chem. 8 (2004) 910. [16] A. Yazdani, M.R. Jalilian Nosrati, R. Ghasemi, J. Magn. Magn. Mater. 304 (2006) 433. [17] L.D. Tung, V. Kolesnichenko, G. Caruntu, D. Caruntu, Y. Remond, V.O. Golub, C.J. O’Connor, L. Spinu, Physica B 319 (2002) 116. [18] A. Thakur, M. Singh, Ceram. Int. 29 (2003) 505. [19] C. Guillaud, J. Phys. Radium 12 (3) (1951) 239. [20] A.E. Virden, K. O’Grady, J. Magn. Magn. Mater. 290–291 (2005) 868.