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57Fe Mössbauer spectroscopy of pseudo-1D sulfide of FePb4Sb6S14
ARTICLE IN PRESS
Journal of Magnetism and Magnetic Materials 310 (2007) e962–e964 www.elsevier.com/locate/jmmm
57
Fe Mo¨ssbauer spectroscopy of pseudo-1D sulfide of FePb4Sb6S14 S. Morimotoa,b,, Y. Matsushitac,d, Y. Uedac, M. Kawasee, T. Saitob, S. Nakamuraf,g, S. Nasua,b a
Graduatte of School of Engineering Science, Osaka University, Toyonaka, Osaka 560-8531, Japan b Radioisotope Research Center, Osaka University, Toyonaka, Osaka 560-0043, Japan c Institute for Solid State Physics, University of Tokyo, Kashiwa, Chiba 277-8581, Japan d Quantum Beam Center, National Institute for Materials Science, Tsukuba, Ibaraki 305-0047, Japan e Fdepartment of Pharmacy, Osaka Ohtani University, Tondabayashi, Osaka 584-8540, Japan f Depatment of Physics, Teikyo Uniersity, Utsunomiya 320-8551, Japan g Advanced Research Institute of Science and Engineering, Waseda University, Shinjuku-ku, Tokyo 169-8555, Japan Available online 20 November 2006
Abstract The magnetic properties of a pseudo-1D system were examined by 57Fe Mo¨ssbauer spectroscopy at various temperatures for Jamesonite, Fe2+Pb4Sb6S14. The spectra above 20 K are paramagnetic and those below 10 K consist of two components: (i) a complexsplit spectra with a large quadrupole split and small hyperfine field as the dominant component and (ii) a sextet with a large hyperfine field and very small quadrupole split. The hyperfine parameters of the low-temperature spectra are discussed from the point of view of valence and spin state in Fe. r 2006 Elsevier B.V. All rights reserved. PACS: 76.80.+y Keywords: Iron; Sulfide; Jamesonite; Mo¨ssbauer effect; 1D system
FePb4Sb6S14, Jamesonite, contains one magnetic element of Fe in formally divalent state (Fe2+) on the assumption of Pb2+, Sb3+ and S2. The crystal structure was reported first by Niizeki and Buerger [1]. Recently, the crystal structure was refined by Matsushita and Ueda [2,3] with a synthetic specimen and by Le´one et al. [4] with a natural specimen . Jamesonite has a monoclinic structure characterized by a 1D chain of edge-shared [FeS6] octahedra along c-axis [0 0 1]. While the Fe–Fe distance is ca. 0.4 nm in the chain; those between the chains are ca. 1.2 nm for [1 1 0] and ca. 1.5 nm for [0 1 0]. Thus this compound is considered to be a pseudo-1D system. Matsushita and Ueda [2,3] reported the DC-magnetic susceptibility with a broad maximum at 33.5 K and anomalies at 3 and 8 K [2,3]. They fitted the temperature Corresponding author. Graduatte of School of Engineering Science, Osaka University, Toyonaka, Osaka 560-8531, Japan. Tel.: +81 6 6850 6451; fax: +81 6 6845 4632. E-mail address: [email protected] (S. Morimoto).
0304-8853/$ - see front matter r 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.jmmm.2006.10.1008
dependence of the DC susceptibility using S ¼ 2 and 1D HAF (Heisenberg anti-ferromagnetic) model. The effective magnetic moment, peff, is estimated to be 4.41 mB, which value suggested a high-spin state of Fe2+ (peff ¼ 4.9 mB) [2,3]. They attributed the maximum at 33.5 K to a shortrange order in the 1D chain and the anomaly at 3 K to a possible spin-glass transition [3]. Le´one et al. [4] reported a similar DC susceptibility with a broad maximum at 30 K and an anomaly at 5 K. They observed an increase on the background in the neutron diffraction pattern below 30 K and magnetic reflections at less than 6 K. They concluded a 3D magnetic order at less than 6 K and a 1D magnetic order or correlations below 30 K developed. For detailed investigation on the magnetic properties, we clarified temperature dependence of 57Fe Mo¨ssbauer spectra. The temperature range was from room temperature to 4 K. The specimen with 20%-enriched 57Fe was synthesized by the similar procedure reported previously [2,3]. We observed two components below 10 K. One was the component (i) of a complex shape with small hyperfine field
ARTICLE IN PRESS S. Morimoto et al. / Journal of Magnetism and Magnetic Materials 310 (2007) e962–e964
and large quadrupole interaction. The other was the component (ii) of a sextet with large hyperfine field. We should note that asymmetry in the paramagnetic spectra does not come from a texture or a preferred orientation of the crystals. The temperature dependence of the Mo¨ssbauer spectra is shown in Fig. 1. The component (i) arose at less than 20 K and the component (ii) did at less than 15 K in the Mo¨ssbauer spectra, thus the magnetic-order temperature was concluded to be a temperature between 20 and 15 K. The Mo¨ssbauer spectroscopy did not detect any development of the short-range magnetic order or the 1D magnetic order reported previously [2–4]. The magnetic components in the Mo¨ssbauer spectra can be attributed to
Fig. 1. The Mo¨ssubaer spectra of the synthetic Jamesonite (FePb4Sb6S14) at various temperatures.
e963
the development of a spin-glass state and the 3D magnetic order mentioned above. The Mo¨ssbauer spectroscopy, thus, revealed clearly a microscopic development of a magnetic order at the Fe site. The temperature discrepancy probably comes from because of a difference in the microscopic sensitivity. The component (i) at 4 K had the isomer shift of 0.89 mm/s. The hyperfine field was roughly estimated to be 16–17 T on the assumptions of the asymmetric parameter, Z, of 0, the angle, y, of 301. Between the direction of the hyperfine field and that of the electric-field gradient, Vzz and the quadrupole interaction of 1.3 mm/s. The component (ii) at 4 K had the isomer shift of 0.64 mm/s and the hyperfine field of 34 T. The ratios of the components (i) and (ii) to the total absorption were determined to be 78% and 13% at 4 K. Contrary to the one crystallographic site for Fe, we observed two components at lower temperatures. If the component (ii) was ascribed to an impurity, the contribution over 10% would make significant effect on the paramagnetic spectra. The preliminary Mo¨ssbuaer measurements on the sample without enrichment gave the identical spectra. The possibility of an impurity, thus, is not plausible at the moment. The component (ii) can be ascribed to the Fe site in the vicinity of possible defects which defects cut the 1D chain. The isomer shift of the (major) component (i) was a characteristic value for Fe2+ and a hyperfine split indicated a high-spin state. For the (minor) component (ii), the Mo¨ssbauer parameters are plotted as a function of temperature in Fig. 2. The isomer shift and the hyperfine field were in between the typical values for Fe3+ and Fe2+ for sulfides. The valence state of the component (ii) is deduced to be an intermediate state between Fe3+ and
Fig. 2. The Mo¨ssubaer parameters of magnetic sextet of the synthetic Jamesonite (FePb4Sb6S14) at lower temperatures. The dashed lines are guides for eyes.
ARTICLE IN PRESS e964
S. Morimoto et al. / Journal of Magnetism and Magnetic Materials 310 (2007) e962–e964
Fe2+. An unusual decrease in the hyperfine fields at lower temperatures was observed. We should note that the hyperfine field of the component (i) also tended to decrease at lower temperatures. The similar decrease implies that both the components probably are intrinsic. The possible explanation of the decrease is the increase of an orbital contribution from an orbital moment of Fe2+-like character. The low-temperature Mo¨ssbauer spectra for the synthetic Jamesonite consisted of the two components: the component (i) of Fe2+ in the high-spin state as the major component and the component (ii) of an intermediate state due to the possible defects. The unusual decrease in the
hyperfine fields at lower temperatures was observed for both components (i) and (ii). The author (S.M.) expresses his thanks to the Low Temperature Center of Osaka University for the help on the measurements at lower temperatures. References [1] [2] [3] [4]
N. Niizeki, M.J. Buerger, Z. Kristallogr. 109 (1957) 161. Y. Matsushita, Y. Ueda, Inorg. Chem. 42 (2003) 7830. Y. Matsushita, Y. Ueda, Prog. Theor. Phys. 159 (2005) 179. P. Le´one, et al., Solid State Sci. 5 (2003) 771.
Journal of Magnetism and Magnetic Materials 310 (2007) e962–e964 www.elsevier.com/locate/jmmm
57
Fe Mo¨ssbauer spectroscopy of pseudo-1D sulfide of FePb4Sb6S14 S. Morimotoa,b,, Y. Matsushitac,d, Y. Uedac, M. Kawasee, T. Saitob, S. Nakamuraf,g, S. Nasua,b a
Graduatte of School of Engineering Science, Osaka University, Toyonaka, Osaka 560-8531, Japan b Radioisotope Research Center, Osaka University, Toyonaka, Osaka 560-0043, Japan c Institute for Solid State Physics, University of Tokyo, Kashiwa, Chiba 277-8581, Japan d Quantum Beam Center, National Institute for Materials Science, Tsukuba, Ibaraki 305-0047, Japan e Fdepartment of Pharmacy, Osaka Ohtani University, Tondabayashi, Osaka 584-8540, Japan f Depatment of Physics, Teikyo Uniersity, Utsunomiya 320-8551, Japan g Advanced Research Institute of Science and Engineering, Waseda University, Shinjuku-ku, Tokyo 169-8555, Japan Available online 20 November 2006
Abstract The magnetic properties of a pseudo-1D system were examined by 57Fe Mo¨ssbauer spectroscopy at various temperatures for Jamesonite, Fe2+Pb4Sb6S14. The spectra above 20 K are paramagnetic and those below 10 K consist of two components: (i) a complexsplit spectra with a large quadrupole split and small hyperfine field as the dominant component and (ii) a sextet with a large hyperfine field and very small quadrupole split. The hyperfine parameters of the low-temperature spectra are discussed from the point of view of valence and spin state in Fe. r 2006 Elsevier B.V. All rights reserved. PACS: 76.80.+y Keywords: Iron; Sulfide; Jamesonite; Mo¨ssbauer effect; 1D system
FePb4Sb6S14, Jamesonite, contains one magnetic element of Fe in formally divalent state (Fe2+) on the assumption of Pb2+, Sb3+ and S2. The crystal structure was reported first by Niizeki and Buerger [1]. Recently, the crystal structure was refined by Matsushita and Ueda [2,3] with a synthetic specimen and by Le´one et al. [4] with a natural specimen . Jamesonite has a monoclinic structure characterized by a 1D chain of edge-shared [FeS6] octahedra along c-axis [0 0 1]. While the Fe–Fe distance is ca. 0.4 nm in the chain; those between the chains are ca. 1.2 nm for [1 1 0] and ca. 1.5 nm for [0 1 0]. Thus this compound is considered to be a pseudo-1D system. Matsushita and Ueda [2,3] reported the DC-magnetic susceptibility with a broad maximum at 33.5 K and anomalies at 3 and 8 K [2,3]. They fitted the temperature Corresponding author. Graduatte of School of Engineering Science, Osaka University, Toyonaka, Osaka 560-8531, Japan. Tel.: +81 6 6850 6451; fax: +81 6 6845 4632. E-mail address: [email protected] (S. Morimoto).
0304-8853/$ - see front matter r 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.jmmm.2006.10.1008
dependence of the DC susceptibility using S ¼ 2 and 1D HAF (Heisenberg anti-ferromagnetic) model. The effective magnetic moment, peff, is estimated to be 4.41 mB, which value suggested a high-spin state of Fe2+ (peff ¼ 4.9 mB) [2,3]. They attributed the maximum at 33.5 K to a shortrange order in the 1D chain and the anomaly at 3 K to a possible spin-glass transition [3]. Le´one et al. [4] reported a similar DC susceptibility with a broad maximum at 30 K and an anomaly at 5 K. They observed an increase on the background in the neutron diffraction pattern below 30 K and magnetic reflections at less than 6 K. They concluded a 3D magnetic order at less than 6 K and a 1D magnetic order or correlations below 30 K developed. For detailed investigation on the magnetic properties, we clarified temperature dependence of 57Fe Mo¨ssbauer spectra. The temperature range was from room temperature to 4 K. The specimen with 20%-enriched 57Fe was synthesized by the similar procedure reported previously [2,3]. We observed two components below 10 K. One was the component (i) of a complex shape with small hyperfine field
ARTICLE IN PRESS S. Morimoto et al. / Journal of Magnetism and Magnetic Materials 310 (2007) e962–e964
and large quadrupole interaction. The other was the component (ii) of a sextet with large hyperfine field. We should note that asymmetry in the paramagnetic spectra does not come from a texture or a preferred orientation of the crystals. The temperature dependence of the Mo¨ssbauer spectra is shown in Fig. 1. The component (i) arose at less than 20 K and the component (ii) did at less than 15 K in the Mo¨ssbauer spectra, thus the magnetic-order temperature was concluded to be a temperature between 20 and 15 K. The Mo¨ssbauer spectroscopy did not detect any development of the short-range magnetic order or the 1D magnetic order reported previously [2–4]. The magnetic components in the Mo¨ssbauer spectra can be attributed to
Fig. 1. The Mo¨ssubaer spectra of the synthetic Jamesonite (FePb4Sb6S14) at various temperatures.
e963
the development of a spin-glass state and the 3D magnetic order mentioned above. The Mo¨ssbauer spectroscopy, thus, revealed clearly a microscopic development of a magnetic order at the Fe site. The temperature discrepancy probably comes from because of a difference in the microscopic sensitivity. The component (i) at 4 K had the isomer shift of 0.89 mm/s. The hyperfine field was roughly estimated to be 16–17 T on the assumptions of the asymmetric parameter, Z, of 0, the angle, y, of 301. Between the direction of the hyperfine field and that of the electric-field gradient, Vzz and the quadrupole interaction of 1.3 mm/s. The component (ii) at 4 K had the isomer shift of 0.64 mm/s and the hyperfine field of 34 T. The ratios of the components (i) and (ii) to the total absorption were determined to be 78% and 13% at 4 K. Contrary to the one crystallographic site for Fe, we observed two components at lower temperatures. If the component (ii) was ascribed to an impurity, the contribution over 10% would make significant effect on the paramagnetic spectra. The preliminary Mo¨ssbuaer measurements on the sample without enrichment gave the identical spectra. The possibility of an impurity, thus, is not plausible at the moment. The component (ii) can be ascribed to the Fe site in the vicinity of possible defects which defects cut the 1D chain. The isomer shift of the (major) component (i) was a characteristic value for Fe2+ and a hyperfine split indicated a high-spin state. For the (minor) component (ii), the Mo¨ssbauer parameters are plotted as a function of temperature in Fig. 2. The isomer shift and the hyperfine field were in between the typical values for Fe3+ and Fe2+ for sulfides. The valence state of the component (ii) is deduced to be an intermediate state between Fe3+ and
Fig. 2. The Mo¨ssubaer parameters of magnetic sextet of the synthetic Jamesonite (FePb4Sb6S14) at lower temperatures. The dashed lines are guides for eyes.
ARTICLE IN PRESS e964
S. Morimoto et al. / Journal of Magnetism and Magnetic Materials 310 (2007) e962–e964
Fe2+. An unusual decrease in the hyperfine fields at lower temperatures was observed. We should note that the hyperfine field of the component (i) also tended to decrease at lower temperatures. The similar decrease implies that both the components probably are intrinsic. The possible explanation of the decrease is the increase of an orbital contribution from an orbital moment of Fe2+-like character. The low-temperature Mo¨ssbauer spectra for the synthetic Jamesonite consisted of the two components: the component (i) of Fe2+ in the high-spin state as the major component and the component (ii) of an intermediate state due to the possible defects. The unusual decrease in the
hyperfine fields at lower temperatures was observed for both components (i) and (ii). The author (S.M.) expresses his thanks to the Low Temperature Center of Osaka University for the help on the measurements at lower temperatures. References [1] [2] [3] [4]
N. Niizeki, M.J. Buerger, Z. Kristallogr. 109 (1957) 161. Y. Matsushita, Y. Ueda, Inorg. Chem. 42 (2003) 7830. Y. Matsushita, Y. Ueda, Prog. Theor. Phys. 159 (2005) 179. P. Le´one, et al., Solid State Sci. 5 (2003) 771.