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Preparation and characterization of La0.7AE0.3MnO3 (AE=Ca, Sr, Ba): Perovskite structured manganites
ARTICLE IN PRESS
Journal of Magnetism and Magnetic Materials 310 (2007) 2668–2670 www.elsevier.com/locate/jmmm
Preparation and characterization of La0.7AE0.3MnO3 (AE ¼ Ca, Sr, Ba): Perovskite structured manganites H.S. Ima, G.B. Chona, Sang M. Leea, B.H. Kooa, C.G. Leea,, M.H. Jungb a
School of Nano and Advanced Materials Engineering, Changwon National University, Changwon 641-773, Republic of Korea b Material Research Team, Korea Basic Science Institute, Daejeon 305-333, Republic of Korea Available online 4 January 2007
Abstract Perovskite structured manganites, La0.7AE0.3MnO3 (AE ¼ Ba, Ca, Sr), were prepared by using a solid-state reaction method. X-ray diffraction patterns of the La0.7Ca0.3MnO3 showed orthorhombic system, but La0.7Ba0.3MnO3 and La0.7Sr0.3MnO3 showed rhombohedral system at room temperature. Scanning electron microscopy of La0.7Ca0.3MnO3 and La0.7Sr0.3MnO3 showed smooth and densified structures but La0.7Ba0.3MnO3 showed coarse structure, clean and pure images. The Curie temperature of La0.7Ba0.3MnO3 was 290 K, that of La0.7Ca0.3MnO3 was 240 K and that of La0.7Sr0.3 MnO3 was 350 K. In this research, we investigated the effect of A-site substitution by alkaline-earth elements on the Curie temperature from the point of Mn–O bond length. r 2007 Elsevier B.V. All rights reserved. PACS: 75.90.+w; 75.30.Kz; 75.30.m Keywords: La0.7(Ca; Sr; Ba)0.3MnO3; Curie temperature; Colossal magnetoresistance (CMR)
1. Introduction With advances in information technology, more sensitive and high magnetoresistive materials are required for highspeed electronic and magnetic devices. Within those materials, perovskite structured manganites (general formula of A1XBXMnO3 with A ¼ rare metals and B ¼ alkaline-earth metals) have attracted much attention owing to their colossal magnetoresistance (CMR) behavior around a Curie temperature (Tc) near room temperature and owing to their unique properties [1]. For these material systems, the phase transition temperature Tc is in a large range, strongly dependent on the A-site ions. However, CMR materials require their specific character with high phase transition temperature Tc under low applied field. Therefore, many researches are focused especially on manganites in different forms [2–4]. In manganites, the CMR effect is optimized for samples with a molar ratio of X ¼ 0.33 [3]. As with their forms, their properties vary with precursor materials. Corresponding author. Tel.: +82 55 262 7209; fax: +82 55 261 7017.
E-mail address: [email protected] (C.G. Lee). 0304-8853/$ - see front matter r 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.jmmm.2006.12.002
In this study, we prepared particles of La0.7Ba0.3MnO3, La0.7Ca0.3MnO3 and La0.7Sr0.3MnO3 by using solid-state reaction method, and investigated the effect of A-site substitution by alkaline-earth elements on the Curie temperature. 2. Experimental The mixture of La2O3 (0.0035 mol), BaCO3 (0.03 mol) or CaCO3 (0.03 mol) or SrCO3 (0.03 mol), and Mn2O3 (0.010 mol) was mixed and ball-milled for 24 h. Thermogravimetric analyzer was used to determine the crystallization temperature. The calcination in a furnace was performed at 1000 1C for 6 h. After the reaction mixtures were cooled down to room temperature, the obtained products were washed several times with distilled water and finally with ethanol. The sintering in the furnace was performed at 1200 1C for 24 h. After dried at 103 1C for 24 h, fine powders of final products were obtained. The final products were analyzed and characterized by X-ray diffractometer (XRD), energy-dispersive analysis (EDS), scanning electron microscopy (SEM) and superconducting quantum interference device.
ARTICLE IN PRESS H.S. Im et al. / Journal of Magnetism and Magnetic Materials 310 (2007) 2668–2670
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3. Results and discussion The EDS analysis showed that the relative molar ratios of all three manganites were close to 0.7:0.3:1.0, which is the starting molar composition. XRD patterns of manganites are shown in Fig. 1. XRD patterns of La0.7Ca0.3 MnO3 and La0.7Sr0.3MnO3 showed homogeneous phase, while La0.7Ba0.3MnO3 showed inhomogeneous phase after calcination in the furnace at 1000 1C for 6 h. After sintering at 1200 1C for 24 h, homogeneous phase was obtained without any other impurity phase. Fig. 1 shows the results of XRD for La0.7Sr0.3MnO3, La0.7Ba0.3MnO3 and La0.7Ca0.3MnO3. The diffraction pattern showed some differences between those compounds as indicated in the inset of Fig. 1; La0.7Ca0.3MnO3 showed orthorhombic system, but La0.7Ba0.3MnO3 and La0.7Sr0.3MnO3 showed rhombohedral system at room temperature [5]. The SEM images of manganites showed that samples are made up of particles with various grain sizes (Fig. 2). La0.7Ca0.3MnO3 and La0.7Sr0.3MnO3 showed smooth and densified structures but La0.7Ba0.3MnO3 showed a coarse structure. This result might be caused by the reason that the atomic radius of Ba is much bigger and the activation energy of Ba is higher than that of Ca and Sr; thus, Ba atom reacts worse with other existing metals (La and Mn). Therefore, La0.7Ba0.3MnO3 requires higher sintering energy to get perovskite structure [6]. Magnetization curves for La0.7Ba0.3MnO3, La0.7Ca0.3 MnO3 and La0.7Sr0.3MnO3 are shown in Fig. 3. La0.7Ca0.3 MnO3 showed the highest saturated magnetization values
(c) (b) (a)
20
30
40
50
60
70
80
Fig. 1. XRD patterns of (a) La0.7Ba0.3MnO3, (b) La0.7Sr0.3MnO3 and (c) La0.7Ca0.3MnO3 (after sintering at 1200 1C for 24 h).
200
12 10
150
(c)
(a)
8
100
6 (b)
50
4 2
0
0
50
100
150
200
250
300
350
0
Fig. 3. Magnetization as a function of temperature of (a) La0.7Ba0.3 MnO3, (b) La0.7Sr0.3MnO3 and (c) La0.7Ca0.3MnO3.
Table 1 Ionic radius of elements involved in perovskite-like manganites
LCMO LSMO LBMO
rA (A˚)
Mn–O (A˚)
Tc (K)
1.210 1.244 1.292
1.969 1.955 1.962
250 350 290
around 200 emu/g at a temperature below 213 K, and magnetization values fall around zero at 240 K. La0.7Sr0.3MnO3 showed the lowest saturated magnetization values around 5 emu/g and fall around zero at 350 K. The Tc of La0.7Ba0.3MnO3 is observed around 290 K, Tc of La0.7Ca0.3MnO3 observed around 240 K and that of La0.7Sr0.3MnO3 observed around 350 K and the values are lower than those of a reported value [7]. The Curie temperature is affected by bond strength between Mn and O ions. As shown in Table 1, the bond lengths between Mn and O change with the radius of ions substituted in A site.
4. Conclusions La0.7Ba0.3MnO3, La0.7Ca0.3MnO3 and La0.7Sr0.3MnO3 by solid-state reaction method and their properties were measured with pelletized samples. The Curie temperature of La0.7Ba0.3MnO3 was 290 K, of La0.7Ca0.3MnO3 was 240 K and that of La0.7Sr0.3 MnO3 was 350 K.
Acknowledgment
Fig. 2. SEM images of (a) La0.7Ba0.3MnO3, (b) La0.7Sr0.3MnO3 and (c) La0.7Ca0.3MnO3 (after sintering at 1200 1C for 24 h).
This work was supported by grant no. RTI04-01-03 from the Regional Technology Innovation Program of the Ministry of Commerce, Industry and Energy (MOCIE).
ARTICLE IN PRESS 2670
H.S. Im et al. / Journal of Magnetism and Magnetic Materials 310 (2007) 2668–2670
References [1] Y.H. Li, K.A. Thomas, P.S.I.P.N. de Silva, L.F. Cohen, A. Goyal, M. Rajeswari, N.D. Mathur, M.G. Blamire, J.E. Evetts, T. Venkatesan, J.L. MacManus-Driscoll, J. Mater. Res. 13 (8) (1998) 2161. [2] T. Zhang, C.G. Jin, T. Qian, X.L. Lu, J.M. Bai, X.G. Li, J. Mater. Chem. 14 (2004) 2787. [3] Z.X. Cheng, H.F. Zhen, A.H. Li, X.L. Wang, H. Kimura, J. Crystal Growth 275 (2005) 2415.
[4] S. Bae, S.X. Wang, Appl. Phys. Lett. 69 (1) (1996) 121. [5] P.G. Radaelli, G. Iannone, M. Marezio, H.Y. Hwang, S.-W. Cheong, J.D. Jorgensen, D.N. Argyriou, Phys. Rev. B 56 (13) (1997) 8265. [6] A.N. Ulyanov, S.C. Yu, S.G. Min, G.G. Levchenko, J. Appl. Phys. 91 (2002) 7926. [7] T.-L. Phan, N.V. Khiem, J. Zidanic, N.X. Phuc, S.-C. Yu, IEEE Trans. Magn. 41 (10) (2005) 2769.
Journal of Magnetism and Magnetic Materials 310 (2007) 2668–2670 www.elsevier.com/locate/jmmm
Preparation and characterization of La0.7AE0.3MnO3 (AE ¼ Ca, Sr, Ba): Perovskite structured manganites H.S. Ima, G.B. Chona, Sang M. Leea, B.H. Kooa, C.G. Leea,, M.H. Jungb a
School of Nano and Advanced Materials Engineering, Changwon National University, Changwon 641-773, Republic of Korea b Material Research Team, Korea Basic Science Institute, Daejeon 305-333, Republic of Korea Available online 4 January 2007
Abstract Perovskite structured manganites, La0.7AE0.3MnO3 (AE ¼ Ba, Ca, Sr), were prepared by using a solid-state reaction method. X-ray diffraction patterns of the La0.7Ca0.3MnO3 showed orthorhombic system, but La0.7Ba0.3MnO3 and La0.7Sr0.3MnO3 showed rhombohedral system at room temperature. Scanning electron microscopy of La0.7Ca0.3MnO3 and La0.7Sr0.3MnO3 showed smooth and densified structures but La0.7Ba0.3MnO3 showed coarse structure, clean and pure images. The Curie temperature of La0.7Ba0.3MnO3 was 290 K, that of La0.7Ca0.3MnO3 was 240 K and that of La0.7Sr0.3 MnO3 was 350 K. In this research, we investigated the effect of A-site substitution by alkaline-earth elements on the Curie temperature from the point of Mn–O bond length. r 2007 Elsevier B.V. All rights reserved. PACS: 75.90.+w; 75.30.Kz; 75.30.m Keywords: La0.7(Ca; Sr; Ba)0.3MnO3; Curie temperature; Colossal magnetoresistance (CMR)
1. Introduction With advances in information technology, more sensitive and high magnetoresistive materials are required for highspeed electronic and magnetic devices. Within those materials, perovskite structured manganites (general formula of A1XBXMnO3 with A ¼ rare metals and B ¼ alkaline-earth metals) have attracted much attention owing to their colossal magnetoresistance (CMR) behavior around a Curie temperature (Tc) near room temperature and owing to their unique properties [1]. For these material systems, the phase transition temperature Tc is in a large range, strongly dependent on the A-site ions. However, CMR materials require their specific character with high phase transition temperature Tc under low applied field. Therefore, many researches are focused especially on manganites in different forms [2–4]. In manganites, the CMR effect is optimized for samples with a molar ratio of X ¼ 0.33 [3]. As with their forms, their properties vary with precursor materials. Corresponding author. Tel.: +82 55 262 7209; fax: +82 55 261 7017.
E-mail address: [email protected] (C.G. Lee). 0304-8853/$ - see front matter r 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.jmmm.2006.12.002
In this study, we prepared particles of La0.7Ba0.3MnO3, La0.7Ca0.3MnO3 and La0.7Sr0.3MnO3 by using solid-state reaction method, and investigated the effect of A-site substitution by alkaline-earth elements on the Curie temperature. 2. Experimental The mixture of La2O3 (0.0035 mol), BaCO3 (0.03 mol) or CaCO3 (0.03 mol) or SrCO3 (0.03 mol), and Mn2O3 (0.010 mol) was mixed and ball-milled for 24 h. Thermogravimetric analyzer was used to determine the crystallization temperature. The calcination in a furnace was performed at 1000 1C for 6 h. After the reaction mixtures were cooled down to room temperature, the obtained products were washed several times with distilled water and finally with ethanol. The sintering in the furnace was performed at 1200 1C for 24 h. After dried at 103 1C for 24 h, fine powders of final products were obtained. The final products were analyzed and characterized by X-ray diffractometer (XRD), energy-dispersive analysis (EDS), scanning electron microscopy (SEM) and superconducting quantum interference device.
ARTICLE IN PRESS H.S. Im et al. / Journal of Magnetism and Magnetic Materials 310 (2007) 2668–2670
2669
14
3. Results and discussion The EDS analysis showed that the relative molar ratios of all three manganites were close to 0.7:0.3:1.0, which is the starting molar composition. XRD patterns of manganites are shown in Fig. 1. XRD patterns of La0.7Ca0.3 MnO3 and La0.7Sr0.3MnO3 showed homogeneous phase, while La0.7Ba0.3MnO3 showed inhomogeneous phase after calcination in the furnace at 1000 1C for 6 h. After sintering at 1200 1C for 24 h, homogeneous phase was obtained without any other impurity phase. Fig. 1 shows the results of XRD for La0.7Sr0.3MnO3, La0.7Ba0.3MnO3 and La0.7Ca0.3MnO3. The diffraction pattern showed some differences between those compounds as indicated in the inset of Fig. 1; La0.7Ca0.3MnO3 showed orthorhombic system, but La0.7Ba0.3MnO3 and La0.7Sr0.3MnO3 showed rhombohedral system at room temperature [5]. The SEM images of manganites showed that samples are made up of particles with various grain sizes (Fig. 2). La0.7Ca0.3MnO3 and La0.7Sr0.3MnO3 showed smooth and densified structures but La0.7Ba0.3MnO3 showed a coarse structure. This result might be caused by the reason that the atomic radius of Ba is much bigger and the activation energy of Ba is higher than that of Ca and Sr; thus, Ba atom reacts worse with other existing metals (La and Mn). Therefore, La0.7Ba0.3MnO3 requires higher sintering energy to get perovskite structure [6]. Magnetization curves for La0.7Ba0.3MnO3, La0.7Ca0.3 MnO3 and La0.7Sr0.3MnO3 are shown in Fig. 3. La0.7Ca0.3 MnO3 showed the highest saturated magnetization values
(c) (b) (a)
20
30
40
50
60
70
80
Fig. 1. XRD patterns of (a) La0.7Ba0.3MnO3, (b) La0.7Sr0.3MnO3 and (c) La0.7Ca0.3MnO3 (after sintering at 1200 1C for 24 h).
200
12 10
150
(c)
(a)
8
100
6 (b)
50
4 2
0
0
50
100
150
200
250
300
350
0
Fig. 3. Magnetization as a function of temperature of (a) La0.7Ba0.3 MnO3, (b) La0.7Sr0.3MnO3 and (c) La0.7Ca0.3MnO3.
Table 1 Ionic radius of elements involved in perovskite-like manganites
LCMO LSMO LBMO
rA (A˚)
Mn–O (A˚)
Tc (K)
1.210 1.244 1.292
1.969 1.955 1.962
250 350 290
around 200 emu/g at a temperature below 213 K, and magnetization values fall around zero at 240 K. La0.7Sr0.3MnO3 showed the lowest saturated magnetization values around 5 emu/g and fall around zero at 350 K. The Tc of La0.7Ba0.3MnO3 is observed around 290 K, Tc of La0.7Ca0.3MnO3 observed around 240 K and that of La0.7Sr0.3MnO3 observed around 350 K and the values are lower than those of a reported value [7]. The Curie temperature is affected by bond strength between Mn and O ions. As shown in Table 1, the bond lengths between Mn and O change with the radius of ions substituted in A site.
4. Conclusions La0.7Ba0.3MnO3, La0.7Ca0.3MnO3 and La0.7Sr0.3MnO3 by solid-state reaction method and their properties were measured with pelletized samples. The Curie temperature of La0.7Ba0.3MnO3 was 290 K, of La0.7Ca0.3MnO3 was 240 K and that of La0.7Sr0.3 MnO3 was 350 K.
Acknowledgment
Fig. 2. SEM images of (a) La0.7Ba0.3MnO3, (b) La0.7Sr0.3MnO3 and (c) La0.7Ca0.3MnO3 (after sintering at 1200 1C for 24 h).
This work was supported by grant no. RTI04-01-03 from the Regional Technology Innovation Program of the Ministry of Commerce, Industry and Energy (MOCIE).
ARTICLE IN PRESS 2670
H.S. Im et al. / Journal of Magnetism and Magnetic Materials 310 (2007) 2668–2670
References [1] Y.H. Li, K.A. Thomas, P.S.I.P.N. de Silva, L.F. Cohen, A. Goyal, M. Rajeswari, N.D. Mathur, M.G. Blamire, J.E. Evetts, T. Venkatesan, J.L. MacManus-Driscoll, J. Mater. Res. 13 (8) (1998) 2161. [2] T. Zhang, C.G. Jin, T. Qian, X.L. Lu, J.M. Bai, X.G. Li, J. Mater. Chem. 14 (2004) 2787. [3] Z.X. Cheng, H.F. Zhen, A.H. Li, X.L. Wang, H. Kimura, J. Crystal Growth 275 (2005) 2415.
[4] S. Bae, S.X. Wang, Appl. Phys. Lett. 69 (1) (1996) 121. [5] P.G. Radaelli, G. Iannone, M. Marezio, H.Y. Hwang, S.-W. Cheong, J.D. Jorgensen, D.N. Argyriou, Phys. Rev. B 56 (13) (1997) 8265. [6] A.N. Ulyanov, S.C. Yu, S.G. Min, G.G. Levchenko, J. Appl. Phys. 91 (2002) 7926. [7] T.-L. Phan, N.V. Khiem, J. Zidanic, N.X. Phuc, S.-C. Yu, IEEE Trans. Magn. 41 (10) (2005) 2769.