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Anisotropic properties of the magnetization and flux dynamics of a spherical single crystal of La1.8Sr0.2CuO4−δ
Physica C 408–410 (2004) 389–391 www.elsevier.com/locate/physc
Anisotropic properties of the magnetization and flux dynamics of a spherical single crystal of La1:8Sr0:2CuO4d A. Gardchareon a
a,b,*
, N. Mangkorntong a, P. Nordblad
a
Department of Materials Science (Solid State Physics), Uppsala University, P.O. Box 534, SE-751 21 Uppsala, Sweden b Department of Physics, Faculty of Sciences, Chiang Mai University, Chiang Mai 50200, Thailand
Abstract Single crystals of La1:8 Sr0:2 CuO4d grown by the traveling solvent floating zone method have been ground to spherical shape for studies of anisotropic supercondcucting properties by SQUID magnetometry. Here, we report on magnetization measurements parallel and perpendicular to the c-axis of one of these crystals. At low enough temperatures and fields the sphere is perfectly shielding (susceptibility )1.5 [SI]) and thus magnetically isotropic. Magnetization vs field experiments reveal a large difference in the hysteresis behavior along the two directions and a surprising enhancement of the critical current density through the CuO planes compared to in-plane at higher fields. Magnetization relaxation curves at low fields and temperatures close to the critical temperature (Tc 29:5 K) show, in both directions, a distorted logarithmic relaxation and a similar power law field dependence of the relaxation rate at low fields followed by a broad maximum. The relaxation rate shows a field and direction dependent maximum at temperatures below Tc . Ó 2004 Elsevier B.V. All rights reserved. PACS: 74.25.Qt; 74.72.Dn; 75.30.Gw Keywords: Flux dynamics; Hysteresis
La2x Srx CuO4d is a high-Tc superconducting compound [1–3] with a crystal structure that contains only one CuO2 plane per primitive cell. The superconductivity of the compound depends strongly on the Sr concentration [2,3] and the physical properties of system have been quite extensively investigated. [4–8] Here, we report results from magnetization measurements parallel and perpendicular to the c-axis of a spherical single crystal of La1:8 Sr0:2 CuO4d with emphasis on anisotropy and flux dynamics. The experiments were performed in two different SQUID-magnetometers: a Quantum Design MPMS5 and a non commercial system specially designed for low field studies of magnetization dynamics [9]. The
* Corresponding author. Address: Department of Materials Science (Solid State Physics), Uppsala University, P.O. Box 534, SE-751 21 Uppsala, Sweden. E-mail address: [email protected] (A. Gardchareon).
single crystal was grown by the traveling solvent floating zone method [10] and out of this crystal, a piece was cut and ground to spherical shape with 1.994 mm diameter. The temperature dependence of zero-field cooled (ZFC), field cooled (FC) and thermo remanent (TRM) magnetization ðMÞ parallel and perpendicular to the caxis of the sample was measured in the temperature range 20–35 K in different applied magnetic fields between 0.01 and 100 Oe and the results for some fields are shown in Fig. 1. The transition temperature ðTc Þ was from these measurements found to be 29.5 K. The sample is perfectly shielding in both directions at low enough fields and temperatures. The transition broadens with increasing magnetic field and the width of the transition is smaller when the field is applied parallel to the c-axis. The flux expulsion (FC magnetization) is weak, but much stronger in the parallel than in the perpendicular direction. It can also be noted that the relation MTRM MFC MZFC is valid.
0921-4534/$ - see front matter Ó 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.physc.2004.02.116
A. Gardchareon et al. / Physica C 408–410 (2004) 389–391
10
H=0.01 Oe H=0.1 Oe H=10 Oe H=0.01 Oe H=0.1 Oe H=10 Oe
1.5 TRM
20
M/H
0.5 0
0.1 Oe
Oe FC 0.01 0.1 Oe 0.01 Oe
0.5
Hm = 2 G
40
S ( arb. units)
1
2 S ( arb. units)
390
10
0 22
24
30
exponent = 1.25 H⊥ caxis H // caxis Tm = 28 K
20
25 T(K)
30
35
Fig. 1. Temperature dependence of the ZFC, FC and TRM Ôsusceptibility’ for the field perpendicular to the c-axis (solid markers) and for the field parallel to the c-axis (open markers), H ¼ 0:01 Oe and 0.1 Oe and the ZFC curves for 10 Oe are also shown.
The field dependence of the magnetization at 20 K is shown in Fig. 2. The behavior at very low fields is for both directions perfectly shielding and the curves have an initial slope of )1.5. At higher fields, as can be seen from the figure, the hysterisis loop is wider parallel to the the c-axis than perpendicular to the c-axis––indicating that the critical current density is higher within the planes than in-between the CuO planes. It is, however, worth to note that at the highest fields of our experiment, the hysterisis loop for the perpendicular field surprisingly becomes wider than the parallel loop!
4
H ( Oe) 10
0
10
1
Fig. 3. Relaxation rate; S vs H (main frame)and S vs T (inset). Data perpendicular to the c-axis (solid circles) and parallel to the c-axis (open circles).
The relaxation of the magnetization in different fields and at different temperatures was measured by cooling the sample in zero field from a temperature above Tc to the measurement temperature (Tm ), where the magnetic field was applied and the magnetization recorded as a function of time after the field application. The relaxation is more or less logarithmic in time. The relaxation rate, S ¼ 1=H ðoDM=o lnðtÞÞ increases with increasing field at low fields. This is illustrated in Fig. 3, where S is plotted vs H at 28 K. The relaxation rate increases with field as H x , with x 1:25 in both directions, but S is larger in the parallel case. The inset shows S vs T from measurements at 2 Oe. The magnitude of the maximum of the S vs T curve is higher and appears at a lower temperature when the magnetic field is applied perpendicular to the c-axis than when it is parallel to the c-axis.
x 10
H⊥caxis H // caxis Tm = 20 K
4
Acknowledgements
2 M ( A/m )
28
ZFC
15
6
26 T (K)
0
1 1.5
// c axis
exponent = 1.25 10
ZFC 10 Oe
1
⊥ c axis
Financial support from the Swedish Research Council (VR) is acknowledged. A.G. acknowledges the ISP of Uppsala University for administrating and the Ministry of Science, Technology and Environment of Thailand for financing a fellowship for research in Sweden.
0 2 4 6 8
References 6
4
2
0 2 H ( A/m )
4
6
8 5 x 10
Fig. 2. Field dependence of magnetization at 20 K when the field is perpendicular to the c-axis (solid circles) and parallel to the c-axis (open circles).
[1] K. Kishio, K. Kitizawa, S. Kanbe, I. Yasuda, N. Sugii, H. Takagi, S. Uchida, K. Fueki, S. Tanaka, Chem. Lett. 16 (1987) 429. [2] J.M. Tarascon, L.H. Green, W.R. McKinnon, G.W. Hull, T.H. Geballe, Science 235 (1987) 1373.
A. Gardchareon et al. / Physica C 408–410 (2004) 389–391 [3] R.B. Van Dover, R.J. Cava, B. Batlogg, E.A. Reitman, Phys. Rev. B 35 (1987) 5337. [4] H. Iwasaki, F. Matsuoka, K. Tanigawa, Phys. Rev. B 59 (1999) 14624. [5] T. Sasagawa, Y. Togawa, J. Shimoyama, A. Kapitulnik, K. Kitazawa, K. Kishio, Phys. Rev. B 61 (2000) 1610. [6] T. Tachiki, K. Nakajima, T. Yamashita, I. Tanaka, H. Kojima, IEEE. Trans. Appl. Supercon. 9 (1999) 2191.
391
[7] B. Lake, H.M. Ronnow, N.B. Chistensen, G. Aeppli, K. Lefmann, D.F. McMorrow, P. Vorderwisch, P. Smeibidl, N. Mangkorntong, T. Sasagawa, M. Nohara, H. Takagi, T.E. Mason, Nature 415 (2002) 299. [8] Y.M. Huh, D.K. Finnemore, Phys. Rev. B 65 (2002) 092506. [9] J. Magnusson, C. Djurberg, P. Granberg, P. Nordblad, Rev. Sci. Instr. 68 (1997) 3761. [10] I. Tanaka, H. Kojima, Nature 337 (1989) 21.
Anisotropic properties of the magnetization and flux dynamics of a spherical single crystal of La1:8Sr0:2CuO4d A. Gardchareon a
a,b,*
, N. Mangkorntong a, P. Nordblad
a
Department of Materials Science (Solid State Physics), Uppsala University, P.O. Box 534, SE-751 21 Uppsala, Sweden b Department of Physics, Faculty of Sciences, Chiang Mai University, Chiang Mai 50200, Thailand
Abstract Single crystals of La1:8 Sr0:2 CuO4d grown by the traveling solvent floating zone method have been ground to spherical shape for studies of anisotropic supercondcucting properties by SQUID magnetometry. Here, we report on magnetization measurements parallel and perpendicular to the c-axis of one of these crystals. At low enough temperatures and fields the sphere is perfectly shielding (susceptibility )1.5 [SI]) and thus magnetically isotropic. Magnetization vs field experiments reveal a large difference in the hysteresis behavior along the two directions and a surprising enhancement of the critical current density through the CuO planes compared to in-plane at higher fields. Magnetization relaxation curves at low fields and temperatures close to the critical temperature (Tc 29:5 K) show, in both directions, a distorted logarithmic relaxation and a similar power law field dependence of the relaxation rate at low fields followed by a broad maximum. The relaxation rate shows a field and direction dependent maximum at temperatures below Tc . Ó 2004 Elsevier B.V. All rights reserved. PACS: 74.25.Qt; 74.72.Dn; 75.30.Gw Keywords: Flux dynamics; Hysteresis
La2x Srx CuO4d is a high-Tc superconducting compound [1–3] with a crystal structure that contains only one CuO2 plane per primitive cell. The superconductivity of the compound depends strongly on the Sr concentration [2,3] and the physical properties of system have been quite extensively investigated. [4–8] Here, we report results from magnetization measurements parallel and perpendicular to the c-axis of a spherical single crystal of La1:8 Sr0:2 CuO4d with emphasis on anisotropy and flux dynamics. The experiments were performed in two different SQUID-magnetometers: a Quantum Design MPMS5 and a non commercial system specially designed for low field studies of magnetization dynamics [9]. The
* Corresponding author. Address: Department of Materials Science (Solid State Physics), Uppsala University, P.O. Box 534, SE-751 21 Uppsala, Sweden. E-mail address: [email protected] (A. Gardchareon).
single crystal was grown by the traveling solvent floating zone method [10] and out of this crystal, a piece was cut and ground to spherical shape with 1.994 mm diameter. The temperature dependence of zero-field cooled (ZFC), field cooled (FC) and thermo remanent (TRM) magnetization ðMÞ parallel and perpendicular to the caxis of the sample was measured in the temperature range 20–35 K in different applied magnetic fields between 0.01 and 100 Oe and the results for some fields are shown in Fig. 1. The transition temperature ðTc Þ was from these measurements found to be 29.5 K. The sample is perfectly shielding in both directions at low enough fields and temperatures. The transition broadens with increasing magnetic field and the width of the transition is smaller when the field is applied parallel to the c-axis. The flux expulsion (FC magnetization) is weak, but much stronger in the parallel than in the perpendicular direction. It can also be noted that the relation MTRM MFC MZFC is valid.
0921-4534/$ - see front matter Ó 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.physc.2004.02.116
A. Gardchareon et al. / Physica C 408–410 (2004) 389–391
10
H=0.01 Oe H=0.1 Oe H=10 Oe H=0.01 Oe H=0.1 Oe H=10 Oe
1.5 TRM
20
M/H
0.5 0
0.1 Oe
Oe FC 0.01 0.1 Oe 0.01 Oe
0.5
Hm = 2 G
40
S ( arb. units)
1
2 S ( arb. units)
390
10
0 22
24
30
exponent = 1.25 H⊥ caxis H // caxis Tm = 28 K
20
25 T(K)
30
35
Fig. 1. Temperature dependence of the ZFC, FC and TRM Ôsusceptibility’ for the field perpendicular to the c-axis (solid markers) and for the field parallel to the c-axis (open markers), H ¼ 0:01 Oe and 0.1 Oe and the ZFC curves for 10 Oe are also shown.
The field dependence of the magnetization at 20 K is shown in Fig. 2. The behavior at very low fields is for both directions perfectly shielding and the curves have an initial slope of )1.5. At higher fields, as can be seen from the figure, the hysterisis loop is wider parallel to the the c-axis than perpendicular to the c-axis––indicating that the critical current density is higher within the planes than in-between the CuO planes. It is, however, worth to note that at the highest fields of our experiment, the hysterisis loop for the perpendicular field surprisingly becomes wider than the parallel loop!
4
H ( Oe) 10
0
10
1
Fig. 3. Relaxation rate; S vs H (main frame)and S vs T (inset). Data perpendicular to the c-axis (solid circles) and parallel to the c-axis (open circles).
The relaxation of the magnetization in different fields and at different temperatures was measured by cooling the sample in zero field from a temperature above Tc to the measurement temperature (Tm ), where the magnetic field was applied and the magnetization recorded as a function of time after the field application. The relaxation is more or less logarithmic in time. The relaxation rate, S ¼ 1=H ðoDM=o lnðtÞÞ increases with increasing field at low fields. This is illustrated in Fig. 3, where S is plotted vs H at 28 K. The relaxation rate increases with field as H x , with x 1:25 in both directions, but S is larger in the parallel case. The inset shows S vs T from measurements at 2 Oe. The magnitude of the maximum of the S vs T curve is higher and appears at a lower temperature when the magnetic field is applied perpendicular to the c-axis than when it is parallel to the c-axis.
x 10
H⊥caxis H // caxis Tm = 20 K
4
Acknowledgements
2 M ( A/m )
28
ZFC
15
6
26 T (K)
0
1 1.5
// c axis
exponent = 1.25 10
ZFC 10 Oe
1
⊥ c axis
Financial support from the Swedish Research Council (VR) is acknowledged. A.G. acknowledges the ISP of Uppsala University for administrating and the Ministry of Science, Technology and Environment of Thailand for financing a fellowship for research in Sweden.
0 2 4 6 8
References 6
4
2
0 2 H ( A/m )
4
6
8 5 x 10
Fig. 2. Field dependence of magnetization at 20 K when the field is perpendicular to the c-axis (solid circles) and parallel to the c-axis (open circles).
[1] K. Kishio, K. Kitizawa, S. Kanbe, I. Yasuda, N. Sugii, H. Takagi, S. Uchida, K. Fueki, S. Tanaka, Chem. Lett. 16 (1987) 429. [2] J.M. Tarascon, L.H. Green, W.R. McKinnon, G.W. Hull, T.H. Geballe, Science 235 (1987) 1373.
A. Gardchareon et al. / Physica C 408–410 (2004) 389–391 [3] R.B. Van Dover, R.J. Cava, B. Batlogg, E.A. Reitman, Phys. Rev. B 35 (1987) 5337. [4] H. Iwasaki, F. Matsuoka, K. Tanigawa, Phys. Rev. B 59 (1999) 14624. [5] T. Sasagawa, Y. Togawa, J. Shimoyama, A. Kapitulnik, K. Kitazawa, K. Kishio, Phys. Rev. B 61 (2000) 1610. [6] T. Tachiki, K. Nakajima, T. Yamashita, I. Tanaka, H. Kojima, IEEE. Trans. Appl. Supercon. 9 (1999) 2191.
391
[7] B. Lake, H.M. Ronnow, N.B. Chistensen, G. Aeppli, K. Lefmann, D.F. McMorrow, P. Vorderwisch, P. Smeibidl, N. Mangkorntong, T. Sasagawa, M. Nohara, H. Takagi, T.E. Mason, Nature 415 (2002) 299. [8] Y.M. Huh, D.K. Finnemore, Phys. Rev. B 65 (2002) 092506. [9] J. Magnusson, C. Djurberg, P. Granberg, P. Nordblad, Rev. Sci. Instr. 68 (1997) 3761. [10] I. Tanaka, H. Kojima, Nature 337 (1989) 21.