- Email: [email protected]
Sr concentration dependence of incommensurate elastic magnetic peaks in La2−xSrxCuO4
PCS 1682
Journal of Physics and Chemistry of Solids 60 (1999) 1071–1074
Sr concentration dependence of incommensurate elastic magnetic peaks in La22xSrxCuO4 H. Matsushita a, H. Kimura a, M. Fujita b, K. Yamada b, K. Hirota a,*, Y. Endoh a b
a CREST, Department of Physics, Tohoku University, Sendai 980-8578, Japan Institute for Chemical Research, Kyoto University, Gokasho, Uji 610-0011, Japan
Received 30 November 1998
Abstract Neutron scattering measurements were carried out to study the static magnetic structures of superconducting La22xSrxCuO4 with x 0.10 and 0.13. We found that there exist incommensurate magnetic peaks around (p, p) which start appearing below T*. Combined with previous reports for x 0.10, 0.12 and 0.15, we noticed that T* becomes maximum at x 0.12. The static ˚ for x 0.13, which is considerably shorter than j . 200 A ˚ reported for magnetic correlation length j was estimated to be 88 A x 0.12. q 1999 Elsevier Science Ltd. All rights reserved. Keywords: A. Superconductors; B. Crystal growth; C. Neutron scattering; D. Magnetic properties; D. Superconductivity
1. Introduction It is now well recognized that the high temperature superconductivity (HTSC) in cuprates is realized near the boundary of antiferromagnetic insulator, which is called the Mott insulator. Upon increasing x in La22xSrxCuO4, various important phase transition temperatures consecutively appear such as TN (Ne´el ordering: 0.0 # x , 0.02), TSG (spin glass transition: 0.02 , x , 0.05) and Tc (superconducting transition: x . 0.05). Recently, however, Suzuki et al. [1] and Kimura et al. [2] reported experimental evidences that antiferromagnetic spin-density wave (SDW) and superconductivity coexist below Tc for x 0.10 and 0.12. The SDW state with the incommensurate modulation wave vector, e, is established in the superconducting state, which indicates a coupling between SDW and HTSC. They found that the e value increases as x increases and appears linearly related to Tc as observed in the inelastic magnetic scattering [3]. As the SDW state is enhanced in the vicinity of x 0.12, there have been controversial discussions on the physical origin of SDW with respect to the suppression of HTSC around x 1/8 (1/8 problem). In order to elucidate the coexistence of SDW and * Corresponding author.
superconductivity around x 0.12, we have carried out systematic investigations of SDW at x 0.10 and 0.13, which are complementary to previous studies for x 0.10, 0.12 and 0.15. In this report, we present the first experimental result showing that the SDW state is extended to x 0.13.
2. Experimental Single crystals of La22xSrxCuO4with x 0.10 and 0.13 have been grown using a double-ellipsoidal lamp-image furnace by a traveling solvent floating zone (TSFZ) method. Details of crystal growth were described in Ref. [4]. Most part of the crystals (approximately 0.7 cm 3) were used for neutron-scattering measurements. All the crystals were annealed under O2 flowing at 9008C for 50 h and subsequently at 5008C for 50 h, followed by gradual cooling in the furnace. Thus prepared samples were characterized by measuring their shielding signals with a SQUID magnetometer (Quantum Design MPMS2). After cooling under zero field, magnetic field of 10 Oe was applied perpendicular to the Cu–O plane. Tc (midpoint) were determined to be 27.8 and 32.2 K for x 0.10 and 0.13, respectively. These values are consistent with those of powder samples [5–7]. Neutron-scattering measurements were performed using the triple-axis-spectrometer HER at a cold neutron guide in
0022-3697/99/$ - see front matter q 1999 Elsevier Science Ltd. All rights reserved. PII: S0022-369 7(99)00050-5
1072
H. Matsushita et al. / Journal of Physics and Chemistry of Solids 60 (1999) 1071–1074
Fig. 1. (a) The scan along [010] through an incommensurate elastic peak at (0.62, 0.4975, 0) for x 0.13 at 1.4 and 31.3 K. The horizontal bar at the center of the peak is instrumental-resolution. k is the HWHM of the intrinsic peak. (b) Temperature dependence of the intensity averaged with the two points of the centers of the peak presented in (a). The horizontal solid line shows the background.
JRR-3M (JAERI). The incident energy of neutron beam was fixed at 5 meV. Pyrolytic graphite (PG) crystals were used to monochromate and analyze the white neutron beam. We used a Be-filter to reduce higher-order contamination. Horizontal collimations of 20 0 –B–80 0 –80 0 were used. In this configuration, the FWHM of energy resolution for elastic measurements was about 0.2 meV. Both samples were aligned in the (hk0) zone. In this paper, we use the tetragonal (I4/mmm) notation. The crystals were sealed in aluminum containers with He exchange gas. A top-loading liquid-He cryostat (Orange) was used.
3. Results 3.1. x 0.13 Fig. 1(a) shows scans along [010] through an incommensurate elastic peak for x 0.13 around (0.5 1 e,0.5,0) at 1.4 and 31.3 K. As discovered by Lee et al. [8] for La2CuO41d
(LCO), we confirmed that the incommensurate peaks for x 0.13 are shifted from k 0.5 by Dq 0.03 r.l.u., which we define as the Y-shift. A horizontal bar at the center of the peak indicates the instrumental resolution. Obviously the FWHM of the peak at 1.4 K is larger than the instrumental resolution. To determine an inverse correlation length k defined as the HWHM of the intrinsic peak, observed data were fitted to a Gaussian convoluted with the instrumentalresolution function, in which the constant back ground was ˚ 21 or the static assumed. k was determined to be 0.011(4) A ˚ . Normalizing with the magnetic correlation length j , 88 A volume, we compared the scattering intensity of the elastic peak for x 0.13 with that for x 0.12. We conclude I(x 0.13)/I(x 0.12) , 0.8. In Fig. 1(b), the temperature dependence of the intensity at the peak center is presented. The intensity is averaged with two points near the peak center. A horizontal solid line shows background. T* is estimated to be 20 K, which is lower than Tc. Further, this is lower than that of x 0.12 (T* 30 K) [2].
H. Matsushita et al. / Journal of Physics and Chemistry of Solids 60 (1999) 1071–1074
1073
Fig. 2. (a) The scan along [100] through the vicinity of an incommensurate elastic peak at 1.4 and 33 K. (b) The temperature dependence of the intensity at (20.61, 0.5, 0) of x 0.10.
3.2. x 0.10 Fig. 2 shows the scan along [100] across the predicted incommensurate peak position of (20.61, 0.5, 0) at two temperatures, 1.4 and 33 K for x 0.10. Here the temperature dependence of the intensity at (20.61, 0.5, 0) is also presented. We observed appreciable elastic peaks below T* , 15 K, but we possibly missed the center of elastic peaks in this scan. Therefore, further experiments are necessary for taking a similar “Y-shift” into account in this crystal.
previous reports for x 0.10, 0.12 and 0.15, we noticed that T* becomes maximum at x 0.12. 2. The line width of the SDW elastic peak is presumably sharpest at x 0.12 and considerably broadens at x 0.13. 3. Compared with the results from x 0.12, we deduced the intensity ratio of I(x 0.13)/I(x 0.12) , 0.8. 4. The SDW structure in q space is quite similar to those for x 0.12, 0.13 and LCO (Tc 42 K): the structure is distorted from square to rectangular, the angle between the diagonals being 908 2 f (f , 28).
4. Conclusions At this point, we can point out the following important results, although quantitative studies on the coexistence of SDW and HTSC state is warranted. 1. There exist incommensurate magnetic peaks around (p, p), which start appearing below T*. Combined with
Acknowledgements We thank R.J. Birgeneau, Y.S. Lee and G. Shirane for the stimulating discussions. This work is supported by a GrantIn-Aid for Scientific Research of Monbusyou and Core Research for Evolutional Science and Technology
1074
H. Matsushita et al. / Journal of Physics and Chemistry of Solids 60 (1999) 1071–1074
(CREST) project sponsored by the Japan Science & Technology Cooperation.
References [1] T. Suzuki, T. Goto, K. Chiba, T. Shinoda, T. Fukase, Phys. Rev. B 57 (1998) R3229. [2] H. Kimura, K. Hirota, H. Matsushita, K. Yamada, Y. Endoh, Phys. Rev. B in press.
[3] K. Yamada, C. Lee, K. Kurahashi, J. Wada, S. Wakimoto, S. Ueki, H. Kimura, Y. Endoh, Phys. Rev. B 57 (1998) 6165. [4] S. Hosoya, C.H. Lee, S. Wakimoto, K. Yamada, Y. Endoh, Physica C 235–240 (1994) 547. [5] K. Kumagai, K. Kawano, I. Watanabe, K. Nishiyama, K. Nagamine, J. Supercond. 7 (1994) 63. [6] H. Takagi, T. Ido, S. Ishibashi, M. Yota, S. Uchida, Y. Tokura, Phys. Rev. B 40 (1989) 2254. [7] T. Nagano, Y. Tomioka, Y. Nakayama, K. Kishio, K. Kitazawa, Phys. Rev. B 48 (1993) 9689. [8] Y.S. Lee, private communication.
Journal of Physics and Chemistry of Solids 60 (1999) 1071–1074
Sr concentration dependence of incommensurate elastic magnetic peaks in La22xSrxCuO4 H. Matsushita a, H. Kimura a, M. Fujita b, K. Yamada b, K. Hirota a,*, Y. Endoh a b
a CREST, Department of Physics, Tohoku University, Sendai 980-8578, Japan Institute for Chemical Research, Kyoto University, Gokasho, Uji 610-0011, Japan
Received 30 November 1998
Abstract Neutron scattering measurements were carried out to study the static magnetic structures of superconducting La22xSrxCuO4 with x 0.10 and 0.13. We found that there exist incommensurate magnetic peaks around (p, p) which start appearing below T*. Combined with previous reports for x 0.10, 0.12 and 0.15, we noticed that T* becomes maximum at x 0.12. The static ˚ for x 0.13, which is considerably shorter than j . 200 A ˚ reported for magnetic correlation length j was estimated to be 88 A x 0.12. q 1999 Elsevier Science Ltd. All rights reserved. Keywords: A. Superconductors; B. Crystal growth; C. Neutron scattering; D. Magnetic properties; D. Superconductivity
1. Introduction It is now well recognized that the high temperature superconductivity (HTSC) in cuprates is realized near the boundary of antiferromagnetic insulator, which is called the Mott insulator. Upon increasing x in La22xSrxCuO4, various important phase transition temperatures consecutively appear such as TN (Ne´el ordering: 0.0 # x , 0.02), TSG (spin glass transition: 0.02 , x , 0.05) and Tc (superconducting transition: x . 0.05). Recently, however, Suzuki et al. [1] and Kimura et al. [2] reported experimental evidences that antiferromagnetic spin-density wave (SDW) and superconductivity coexist below Tc for x 0.10 and 0.12. The SDW state with the incommensurate modulation wave vector, e, is established in the superconducting state, which indicates a coupling between SDW and HTSC. They found that the e value increases as x increases and appears linearly related to Tc as observed in the inelastic magnetic scattering [3]. As the SDW state is enhanced in the vicinity of x 0.12, there have been controversial discussions on the physical origin of SDW with respect to the suppression of HTSC around x 1/8 (1/8 problem). In order to elucidate the coexistence of SDW and * Corresponding author.
superconductivity around x 0.12, we have carried out systematic investigations of SDW at x 0.10 and 0.13, which are complementary to previous studies for x 0.10, 0.12 and 0.15. In this report, we present the first experimental result showing that the SDW state is extended to x 0.13.
2. Experimental Single crystals of La22xSrxCuO4with x 0.10 and 0.13 have been grown using a double-ellipsoidal lamp-image furnace by a traveling solvent floating zone (TSFZ) method. Details of crystal growth were described in Ref. [4]. Most part of the crystals (approximately 0.7 cm 3) were used for neutron-scattering measurements. All the crystals were annealed under O2 flowing at 9008C for 50 h and subsequently at 5008C for 50 h, followed by gradual cooling in the furnace. Thus prepared samples were characterized by measuring their shielding signals with a SQUID magnetometer (Quantum Design MPMS2). After cooling under zero field, magnetic field of 10 Oe was applied perpendicular to the Cu–O plane. Tc (midpoint) were determined to be 27.8 and 32.2 K for x 0.10 and 0.13, respectively. These values are consistent with those of powder samples [5–7]. Neutron-scattering measurements were performed using the triple-axis-spectrometer HER at a cold neutron guide in
0022-3697/99/$ - see front matter q 1999 Elsevier Science Ltd. All rights reserved. PII: S0022-369 7(99)00050-5
1072
H. Matsushita et al. / Journal of Physics and Chemistry of Solids 60 (1999) 1071–1074
Fig. 1. (a) The scan along [010] through an incommensurate elastic peak at (0.62, 0.4975, 0) for x 0.13 at 1.4 and 31.3 K. The horizontal bar at the center of the peak is instrumental-resolution. k is the HWHM of the intrinsic peak. (b) Temperature dependence of the intensity averaged with the two points of the centers of the peak presented in (a). The horizontal solid line shows the background.
JRR-3M (JAERI). The incident energy of neutron beam was fixed at 5 meV. Pyrolytic graphite (PG) crystals were used to monochromate and analyze the white neutron beam. We used a Be-filter to reduce higher-order contamination. Horizontal collimations of 20 0 –B–80 0 –80 0 were used. In this configuration, the FWHM of energy resolution for elastic measurements was about 0.2 meV. Both samples were aligned in the (hk0) zone. In this paper, we use the tetragonal (I4/mmm) notation. The crystals were sealed in aluminum containers with He exchange gas. A top-loading liquid-He cryostat (Orange) was used.
3. Results 3.1. x 0.13 Fig. 1(a) shows scans along [010] through an incommensurate elastic peak for x 0.13 around (0.5 1 e,0.5,0) at 1.4 and 31.3 K. As discovered by Lee et al. [8] for La2CuO41d
(LCO), we confirmed that the incommensurate peaks for x 0.13 are shifted from k 0.5 by Dq 0.03 r.l.u., which we define as the Y-shift. A horizontal bar at the center of the peak indicates the instrumental resolution. Obviously the FWHM of the peak at 1.4 K is larger than the instrumental resolution. To determine an inverse correlation length k defined as the HWHM of the intrinsic peak, observed data were fitted to a Gaussian convoluted with the instrumentalresolution function, in which the constant back ground was ˚ 21 or the static assumed. k was determined to be 0.011(4) A ˚ . Normalizing with the magnetic correlation length j , 88 A volume, we compared the scattering intensity of the elastic peak for x 0.13 with that for x 0.12. We conclude I(x 0.13)/I(x 0.12) , 0.8. In Fig. 1(b), the temperature dependence of the intensity at the peak center is presented. The intensity is averaged with two points near the peak center. A horizontal solid line shows background. T* is estimated to be 20 K, which is lower than Tc. Further, this is lower than that of x 0.12 (T* 30 K) [2].
H. Matsushita et al. / Journal of Physics and Chemistry of Solids 60 (1999) 1071–1074
1073
Fig. 2. (a) The scan along [100] through the vicinity of an incommensurate elastic peak at 1.4 and 33 K. (b) The temperature dependence of the intensity at (20.61, 0.5, 0) of x 0.10.
3.2. x 0.10 Fig. 2 shows the scan along [100] across the predicted incommensurate peak position of (20.61, 0.5, 0) at two temperatures, 1.4 and 33 K for x 0.10. Here the temperature dependence of the intensity at (20.61, 0.5, 0) is also presented. We observed appreciable elastic peaks below T* , 15 K, but we possibly missed the center of elastic peaks in this scan. Therefore, further experiments are necessary for taking a similar “Y-shift” into account in this crystal.
previous reports for x 0.10, 0.12 and 0.15, we noticed that T* becomes maximum at x 0.12. 2. The line width of the SDW elastic peak is presumably sharpest at x 0.12 and considerably broadens at x 0.13. 3. Compared with the results from x 0.12, we deduced the intensity ratio of I(x 0.13)/I(x 0.12) , 0.8. 4. The SDW structure in q space is quite similar to those for x 0.12, 0.13 and LCO (Tc 42 K): the structure is distorted from square to rectangular, the angle between the diagonals being 908 2 f (f , 28).
4. Conclusions At this point, we can point out the following important results, although quantitative studies on the coexistence of SDW and HTSC state is warranted. 1. There exist incommensurate magnetic peaks around (p, p), which start appearing below T*. Combined with
Acknowledgements We thank R.J. Birgeneau, Y.S. Lee and G. Shirane for the stimulating discussions. This work is supported by a GrantIn-Aid for Scientific Research of Monbusyou and Core Research for Evolutional Science and Technology
1074
H. Matsushita et al. / Journal of Physics and Chemistry of Solids 60 (1999) 1071–1074
(CREST) project sponsored by the Japan Science & Technology Cooperation.
References [1] T. Suzuki, T. Goto, K. Chiba, T. Shinoda, T. Fukase, Phys. Rev. B 57 (1998) R3229. [2] H. Kimura, K. Hirota, H. Matsushita, K. Yamada, Y. Endoh, Phys. Rev. B in press.
[3] K. Yamada, C. Lee, K. Kurahashi, J. Wada, S. Wakimoto, S. Ueki, H. Kimura, Y. Endoh, Phys. Rev. B 57 (1998) 6165. [4] S. Hosoya, C.H. Lee, S. Wakimoto, K. Yamada, Y. Endoh, Physica C 235–240 (1994) 547. [5] K. Kumagai, K. Kawano, I. Watanabe, K. Nishiyama, K. Nagamine, J. Supercond. 7 (1994) 63. [6] H. Takagi, T. Ido, S. Ishibashi, M. Yota, S. Uchida, Y. Tokura, Phys. Rev. B 40 (1989) 2254. [7] T. Nagano, Y. Tomioka, Y. Nakayama, K. Kishio, K. Kitazawa, Phys. Rev. B 48 (1993) 9689. [8] Y.S. Lee, private communication.