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Synthesis and magnetic properties of Sr4−xBaxMn3O10
ARTICLE IN PRESS
Journal of Magnetism and Magnetic Materials 310 (2007) 1832–1834 www.elsevier.com/locate/jmmm
Synthesis and magnetic properties of Sr4xBaxMn3O10 K. Nishimuraa,b,,1, H. Sakuraib, K. Yoshimuraa, E. Takayama-Muromachib a
Department of Chemistry, Graduate School of Science, Kyoto University, Sakyo-ku, Kyoto 606-8502, Japan Superconducting Materials Center, National Institute for Materials Science, Namiki 1-1, Tsukuba, Ibaraki 305-0044, Japan
b
Available online 13 November 2006
Abstract The magnetic properties of solid solution Sr4xBaxMn3O10 (x ¼ 0, 1, 2, 3 and 4) were investigated. These were well characterized as two-dimensional antiferromagnets with Mn4+ (S ¼ 32). The magnetic susceptibility of every sample showed a broad maximum due to short-range ordering at around 80 K. The kinks in the susceptibility and peaks in the specific heat data indicated TN. The TN increased from 67 to 78 K with increasing x. r 2006 Published by Elsevier B.V. PACS: 61.66.Fn; 68.65.+g Keywords: Antiferromagnet; Low-dimensional magnet; Short-range order; Manganate
1. Introduction Perovskite and layered perovskite manganites were a focus of interests in the past decades because of the presence of colossal magnetoresistance. Ca4Mn3O10 is a layered perovskite phase while A4Mn3O10 (A ¼ Sr, Ba) have another type of two-dimensional structures as illustrated in Fig. 1. Three MnO6 octahedra form a Mn3O12 unit by sharing their faces and the Mn3O12 units are connected with each other by sharing their corners to make the layer in the ac plane. Each layer is separated from others by the Sr or Ba ions. Ba4Mn3O10 is a n ¼ 3 member of Ban+1MnnO3n+1 family where the n ¼ N member, BaMnO3, is a 2 H hexagonal perovskite with one-dimensional magnetism. BaMnO3 is attracting much attention, while the magnetisms of Ba4Mn3O10 and Sr4Mn3O10 have remained mystery. The first report on Sr4Mn3O10 concluded that this compound was an antiferromagnet with TN ¼ 215 K from Corresponding author. Department of Chemistry, Graduate School of Science, Kyoto University, Sakyo-ku, Kyoto 606-8502, Japan. Tel.: +81 774 38 3123; fax: +81 774 38 3125. E-mail address: [email protected] (K. Nishimura). 1 Present address: Institute for Chemical Research, Kyoto Univ., Gokasyo, Uji, Kyoto 611-0011, Japan.
0304-8853/$ - see front matter r 2006 Published by Elsevier B.V. doi:10.1016/j.jmmm.2006.10.617
the temperature dependence of magnetic susceptibility [1]. Quite recently, Tang et al. [2] reinvestigated this compound and showed that this was a low-dimensional magnet with TN ¼ 67 K. The broad maximum in the susceptibility found in the first report was attributed to the evolution of a short-range order. However, the susceptibility data reported by Tang et al. [2] showed a divergence behavior at low temperature suggesting the presence of free spins in their sample. In the case of Ba4Mn3O10, the presence of Ne´el state was confirmed by neutron powder diffractions by two groups [3,4]. TN was determined to be 80 K from the neutron diffraction and specific heat data, but the susceptibility showed a ferromagnetic like increase at 40 K probably reflecting the presence of magnetic impurity. We have succeeded in preparing high-quality Sr4xBaxMn3O10 samples by simple solid-state reactions. To be reported here are the results of susceptibility and specific heat measurements.
2. Experimental Polycrystalline samples of Sr4xBaxMn3O10 (x ¼ 0, 1, 2, 3 and 4) were synthesized by solid-state reactions from stoichiometric mixtures of SrCO3 (99.99%), BaCO3
ARTICLE IN PRESS K. Nishimura et al. / Journal of Magnetism and Magnetic Materials 310 (2007) 1832–1834
1833
Fig. 1. The structure of A4Mn3O10 (A ¼ Sr, Ba).
(99.9%) and Mn2O3. Mn2O3 was made from MnO2 (99.99%) by annealing at 700 1C for 2 days in the air. These were pelletized and sintered in alumina crucibles in the air at 1000, 1200 and 1300 1C for 10 h with intermediate grindings. The final products were quenched to the room temperature. Powder X-ray diffraction (XRD) patterns were taken. The magnetic susceptibility was measured with a quantum design magnetic property measurement system (MPMS) in a magnetic field of 0.1 T from 2 to 300 K. The specific heat was measured with a quantum design physical property measurement system (PPMS) by a heat relaxation method from 2 to 220 K. 3. Results and discussion Phase pure Sr4xBaxMn3O10 (x ¼ 0, 1, 2, 3 and 4) samples were obtained for all x values. The lattice parameters increased monotonically with increasing x from a ¼ 5.4766 A˚, b ¼ 12.4659 A˚ and c ¼ 12.5282 A˚ of Sr4Mn3O10 to a ¼ 5.6850 A˚, b ¼ 13.1284 A˚ and c ¼ 12.7327 A˚ of Ba4Mn3O10.obeying the Vegard’s law. It should be noted that the change in the b (inter-plane) axis is 5.3% while those for a and c axes are 3.8% and 1.6%, respectively. This result supports the two dimensional nature of the system. These samples were all insulators at room temperature. The temperature dependence of the magnetic susceptibility for Sr4xBaxMn3O10 (x ¼ 0, 1, 2, 3 and 4) is shown by Fig. 2(a). No difference between the zero-field cooling (ZFC) and the field cooling (FC) data were observed. The
Fig. 2. (a) The temperature dependence of the magnetic susceptibility of Sr4xBaxMn3O10. The inset shows the dw/dT plots. (b) The temperature dependence of the specific heat of Sr4xBaxMn3O10.
susceptibilities exhibit broad maxima at around 175–195 K and kinks at 67–78 K. The dw/dT plots clarify the presence of kinks in the susceptibility. The broad maxima can be attributed to the short-range orders that are peculiar to low-dimensional magnetic systems. As for Sr4Mn3O10, the kink at 67 K is consistent with that reported by Tang et al. [2]. However, the sharp rise below 40 K observed by Tang et al. [2] is absent in our data. Susceptibility of Ba4Mn3O10 showed a similar behavior, broad maximum at around 170 K and a kink at 78 K. This value is the same as that reported by Boulahya et al. [3]. The anomaly below 40 K reported by Zubkov et al. [4] was not observed in our sample. The temperature dependence of the specific heat for Sr4xBaxMn3O10 is shown in Fig. 2(b). These showed sharp l-type anomalies at the temperatures of the kinks in the magnetic susceptibilities. The data for Sr4Mn3O10 and for Ba4Mn3O10 are consistent with those reported by Tang
ARTICLE IN PRESS 1834
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et al. and by Boulahya et al. [2,3], respectively. The presence of a kink in the magnetic susceptibility and a peak in the specific heat at the same temperature indicates that the TN is at this temperature. We estimated the entropy changes below TN. These were 1.7 J/K, only 15% of 11.5 J/ K expected for Mn4+ (S ¼ 32) systems. It indicates that the most of the magnetic entropy is gained at the short-range order, consistent with the two-dimensional nature of the present systems. In Sr4xBaxMn3O10, the TN increased with increasing x. It appears to be opposite because the inter-plane magnetic interaction is expected to be reduced by large Ba ions. This suggests that the magnetic interactions in the present
system are not determined only by geometrical parameters. It is most probable that the interactions mediated by Mn–O–Sr(Ba)–O–Mn have to taken into account. References [1] N. Floros, M. Hervieu, G.v. Tendeloo, C. Michel, A. Maignan, B. Raveau, Solid State Sci. 2 (2000) 1. [2] Y. Tan, X. Ma, Z. Kou, Y. Sun, N. Di, Z. Cheng, Q. Li, Phys. Rev. B 72 (2005) 132403. [3] K. Boulahya, M. Parras, J.M. Gonzalez-Calbet, U. Amador, J.L. Martinez, M.T. Fernandez-Diaz, Phys. Rev. B 69 (2004) 024418. [4] V.G. Zubkov, A.P. Tyutyunniki, I.F. Berger, V.I. Voronin, G.V. Bazuev, C.A. Moore, P.D. Battle, J. Solid State Chem. 167 (2002) 453.
Journal of Magnetism and Magnetic Materials 310 (2007) 1832–1834 www.elsevier.com/locate/jmmm
Synthesis and magnetic properties of Sr4xBaxMn3O10 K. Nishimuraa,b,,1, H. Sakuraib, K. Yoshimuraa, E. Takayama-Muromachib a
Department of Chemistry, Graduate School of Science, Kyoto University, Sakyo-ku, Kyoto 606-8502, Japan Superconducting Materials Center, National Institute for Materials Science, Namiki 1-1, Tsukuba, Ibaraki 305-0044, Japan
b
Available online 13 November 2006
Abstract The magnetic properties of solid solution Sr4xBaxMn3O10 (x ¼ 0, 1, 2, 3 and 4) were investigated. These were well characterized as two-dimensional antiferromagnets with Mn4+ (S ¼ 32). The magnetic susceptibility of every sample showed a broad maximum due to short-range ordering at around 80 K. The kinks in the susceptibility and peaks in the specific heat data indicated TN. The TN increased from 67 to 78 K with increasing x. r 2006 Published by Elsevier B.V. PACS: 61.66.Fn; 68.65.+g Keywords: Antiferromagnet; Low-dimensional magnet; Short-range order; Manganate
1. Introduction Perovskite and layered perovskite manganites were a focus of interests in the past decades because of the presence of colossal magnetoresistance. Ca4Mn3O10 is a layered perovskite phase while A4Mn3O10 (A ¼ Sr, Ba) have another type of two-dimensional structures as illustrated in Fig. 1. Three MnO6 octahedra form a Mn3O12 unit by sharing their faces and the Mn3O12 units are connected with each other by sharing their corners to make the layer in the ac plane. Each layer is separated from others by the Sr or Ba ions. Ba4Mn3O10 is a n ¼ 3 member of Ban+1MnnO3n+1 family where the n ¼ N member, BaMnO3, is a 2 H hexagonal perovskite with one-dimensional magnetism. BaMnO3 is attracting much attention, while the magnetisms of Ba4Mn3O10 and Sr4Mn3O10 have remained mystery. The first report on Sr4Mn3O10 concluded that this compound was an antiferromagnet with TN ¼ 215 K from Corresponding author. Department of Chemistry, Graduate School of Science, Kyoto University, Sakyo-ku, Kyoto 606-8502, Japan. Tel.: +81 774 38 3123; fax: +81 774 38 3125. E-mail address: [email protected] (K. Nishimura). 1 Present address: Institute for Chemical Research, Kyoto Univ., Gokasyo, Uji, Kyoto 611-0011, Japan.
0304-8853/$ - see front matter r 2006 Published by Elsevier B.V. doi:10.1016/j.jmmm.2006.10.617
the temperature dependence of magnetic susceptibility [1]. Quite recently, Tang et al. [2] reinvestigated this compound and showed that this was a low-dimensional magnet with TN ¼ 67 K. The broad maximum in the susceptibility found in the first report was attributed to the evolution of a short-range order. However, the susceptibility data reported by Tang et al. [2] showed a divergence behavior at low temperature suggesting the presence of free spins in their sample. In the case of Ba4Mn3O10, the presence of Ne´el state was confirmed by neutron powder diffractions by two groups [3,4]. TN was determined to be 80 K from the neutron diffraction and specific heat data, but the susceptibility showed a ferromagnetic like increase at 40 K probably reflecting the presence of magnetic impurity. We have succeeded in preparing high-quality Sr4xBaxMn3O10 samples by simple solid-state reactions. To be reported here are the results of susceptibility and specific heat measurements.
2. Experimental Polycrystalline samples of Sr4xBaxMn3O10 (x ¼ 0, 1, 2, 3 and 4) were synthesized by solid-state reactions from stoichiometric mixtures of SrCO3 (99.99%), BaCO3
ARTICLE IN PRESS K. Nishimura et al. / Journal of Magnetism and Magnetic Materials 310 (2007) 1832–1834
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Fig. 1. The structure of A4Mn3O10 (A ¼ Sr, Ba).
(99.9%) and Mn2O3. Mn2O3 was made from MnO2 (99.99%) by annealing at 700 1C for 2 days in the air. These were pelletized and sintered in alumina crucibles in the air at 1000, 1200 and 1300 1C for 10 h with intermediate grindings. The final products were quenched to the room temperature. Powder X-ray diffraction (XRD) patterns were taken. The magnetic susceptibility was measured with a quantum design magnetic property measurement system (MPMS) in a magnetic field of 0.1 T from 2 to 300 K. The specific heat was measured with a quantum design physical property measurement system (PPMS) by a heat relaxation method from 2 to 220 K. 3. Results and discussion Phase pure Sr4xBaxMn3O10 (x ¼ 0, 1, 2, 3 and 4) samples were obtained for all x values. The lattice parameters increased monotonically with increasing x from a ¼ 5.4766 A˚, b ¼ 12.4659 A˚ and c ¼ 12.5282 A˚ of Sr4Mn3O10 to a ¼ 5.6850 A˚, b ¼ 13.1284 A˚ and c ¼ 12.7327 A˚ of Ba4Mn3O10.obeying the Vegard’s law. It should be noted that the change in the b (inter-plane) axis is 5.3% while those for a and c axes are 3.8% and 1.6%, respectively. This result supports the two dimensional nature of the system. These samples were all insulators at room temperature. The temperature dependence of the magnetic susceptibility for Sr4xBaxMn3O10 (x ¼ 0, 1, 2, 3 and 4) is shown by Fig. 2(a). No difference between the zero-field cooling (ZFC) and the field cooling (FC) data were observed. The
Fig. 2. (a) The temperature dependence of the magnetic susceptibility of Sr4xBaxMn3O10. The inset shows the dw/dT plots. (b) The temperature dependence of the specific heat of Sr4xBaxMn3O10.
susceptibilities exhibit broad maxima at around 175–195 K and kinks at 67–78 K. The dw/dT plots clarify the presence of kinks in the susceptibility. The broad maxima can be attributed to the short-range orders that are peculiar to low-dimensional magnetic systems. As for Sr4Mn3O10, the kink at 67 K is consistent with that reported by Tang et al. [2]. However, the sharp rise below 40 K observed by Tang et al. [2] is absent in our data. Susceptibility of Ba4Mn3O10 showed a similar behavior, broad maximum at around 170 K and a kink at 78 K. This value is the same as that reported by Boulahya et al. [3]. The anomaly below 40 K reported by Zubkov et al. [4] was not observed in our sample. The temperature dependence of the specific heat for Sr4xBaxMn3O10 is shown in Fig. 2(b). These showed sharp l-type anomalies at the temperatures of the kinks in the magnetic susceptibilities. The data for Sr4Mn3O10 and for Ba4Mn3O10 are consistent with those reported by Tang
ARTICLE IN PRESS 1834
K. Nishimura et al. / Journal of Magnetism and Magnetic Materials 310 (2007) 1832–1834
et al. and by Boulahya et al. [2,3], respectively. The presence of a kink in the magnetic susceptibility and a peak in the specific heat at the same temperature indicates that the TN is at this temperature. We estimated the entropy changes below TN. These were 1.7 J/K, only 15% of 11.5 J/ K expected for Mn4+ (S ¼ 32) systems. It indicates that the most of the magnetic entropy is gained at the short-range order, consistent with the two-dimensional nature of the present systems. In Sr4xBaxMn3O10, the TN increased with increasing x. It appears to be opposite because the inter-plane magnetic interaction is expected to be reduced by large Ba ions. This suggests that the magnetic interactions in the present
system are not determined only by geometrical parameters. It is most probable that the interactions mediated by Mn–O–Sr(Ba)–O–Mn have to taken into account. References [1] N. Floros, M. Hervieu, G.v. Tendeloo, C. Michel, A. Maignan, B. Raveau, Solid State Sci. 2 (2000) 1. [2] Y. Tan, X. Ma, Z. Kou, Y. Sun, N. Di, Z. Cheng, Q. Li, Phys. Rev. B 72 (2005) 132403. [3] K. Boulahya, M. Parras, J.M. Gonzalez-Calbet, U. Amador, J.L. Martinez, M.T. Fernandez-Diaz, Phys. Rev. B 69 (2004) 024418. [4] V.G. Zubkov, A.P. Tyutyunniki, I.F. Berger, V.I. Voronin, G.V. Bazuev, C.A. Moore, P.D. Battle, J. Solid State Chem. 167 (2002) 453.