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Irreversibility line in the superconductor RuSr2Gd1.4Ce0.6Cu2O10−δ
Physica C 386 (2003) 65–68 www.elsevier.com/locate/physc
Irreversibility line in the superconductor RuSr2Gd1:4Ce0:6Cu2O10d L. Shi, S.J. Feng, G. Li, X.F. Sun, X.-G. Li
*
Structure Research Laboratory, Department of Materials Science and Engineering, University of Science and Technology of China, Hefei 230026, China
Abstract The resistive transition of the superconductor RuSr2 Gd1:4 Ce0:6 Cu2 O10d is measured under magnetic fields from 0 to 10 T. The results show that the irreversibility line determined from the different reduced resistivity criterion can be fitted well by the expression: Hi ¼ að1 T =Tc Þc . The activation energy (U ) is obtained from the low dissipation parts of the qðT Þ curves using the Arrhenius activation law qðT ; H Þ ¼ q0 ðH Þ expfU ðH Þ½1 T =Tc =kB T g. The U value obtained is smaller than that of other high temperature cuprate superconductors, which may be due to the coexistence of superconductivity and ferromagnetism in RuSr2 Gd1:4 Ce0:6 Cu2 O10d . It is also found that the activation energy can be fitted by U ¼ 157H 0:59 . Ó 2002 Elsevier Science B.V. All rights reserved. PACS: 74.60.Ge; 74.72.Jt; 74.25.Fy Keywords: Ru-1222; Irreversibility line; Flux creep
1. Introduction The irreversibility line, a novel feature that was first reported by M€ uller et al. [1] in the field-temperature phase diagram H ðT Þ of the Ba–La–Cu–O system, defines the boundary between reversible and irreversible regions. The irreversibility line is believed to be strongly dependent on the flux pinning property of the superconductors. The knowledge of this line is not only crucial to an understanding of the flux pinning properties but also important for potential applications of the high temperature superconductors. The recent
discovery of the coexistence of superconductivity and ferromagnetism in a hybrid ruthenate–cuprate RuSr2 Gd1:4 Ce0:6 Cu2 O10d (Ru-1222) with layered perovskite structure has attracted a great deal of interest in the properties of this material [2–5]. The Ru-1222 material exhibits ferromagnetic order at a rather high temperature, TM ¼ 180 K, and becomes superconductive at Tc ¼ 42 K, within the ferromagnetically ordered state [2]. In the present study, the irreversibility line for Ru-1222 is derived from resistance data at magnetic fields from 0 to 10 T and its pinning properties are also investigated. 2. Experimental
*
Corresponding author. Tel./fax: +86-551-3603408. E-mail address: [email protected] (X.-G. Li).
A polycrystalline sample of the RuSr2 Gd1:4 Ce0:6 Cu2 O10d was synthesized by a solid-state
0921-4534/02/$ - see front matter Ó 2002 Elsevier Science B.V. All rights reserved. doi:10.1016/S0921-4534(02)02148-2
L. Shi et al. / Physica C 386 (2003) 65–68
reaction method from a stoichiometric mixture of the powders RuO2 , SrCO3 , Gd2 O3 , CeO2 , and CuO. The mixture was thoroughly ground and diepressed into pellets before preliminary reaction in air at 1000 °C for 36 h. The resulting samples were reground, repelleted, and heated at 1070 °C in flowing oxygen for 60 h, and finally slowly cooled to room temperature. X-ray diffraction (XRD) patterns were measured with a Mac Science MXP18AHF X-ray diffractometer using Cu Ka radiation. The resistance of the samples was measured using a standard four-probe method down to 4.2 K. Magnetoresistance was measured in the magnetic fields of up to 10 T using an Oxford Instruments superconducting magnet.
12
ρ/ρn 20% 10% 0.5% 0.1% 0.01%
9
H (Tesla)
66
6
3
0 3
6
9
12
15
Tirr (K) Fig. 2. The Tirr vs. field H for RuSr2 Gd1:4 Ce0:6 Cu2 O10d at different reduced resistivity criterion. The solid lines denote the fitting results.
3. Results and discussion The powder XRD pattern recorded at room temperature for the sample RuSr2 Gd1:4 Ce0:6 Cu2 O10d reveals that it is nearly single-phase 1222. Fig. 1 shows the resistive transition for Ru-1222 in magnetic fields of up to 10 T. In zero field, the onset superconducting transition temperature TcðonsetÞ and zero resistivity temperature Tcð0Þ are 45 and 16 K, respectively. The resistivity curves broaden gradually, and both Tcð0Þ and TcðonsetÞ decrease with the increasing magnetic field. In Fig. 2, the magnetic field values (H ) are plotted as function of the corresponding irreversibility tempera-
ρ (Ω .cm)
0.02
10T 8T 4T 2T 1T 0T
0.01
0.00
0
20
40
60
T (K) Fig. 1. The temperature dependence of the resistivity for RuSr2 Gd1:4 Ce0:6 Cu2 O10d at various magnetic fields.
tures (Tirr ) which are defined at 0.01%, 0.1%, 0.5%, 10%, 20% of the normal state resistivity (qn ), respectively. We can see that the irreversibility line shifts to lower temperatures with decrease of q=qn It is found that the H –Tirr curves in Fig. 2 can all be fitted well by expression Hi ¼ að1 T =Tc Þc
ð1Þ
where a and c are fitting parameters. The c value is found to increase with decreasing q=qn from 1.3 at q=qn ¼ 20% to 4.5 at q=qn ¼ 0:01%. This power dependence law was also observed in other high temperature superconductors where the exponent c has values ranging from 1.5 to 5.5 for various high Tc families, e.g.: c ¼ 1:5 for YBa2 Cu3 O7 [6]; 2.5 for HgBa2 CaCu2 O6þd [7]; 5.5 for Bi2 Sr2 CaCu2 O8 [8]. The relative large value of c ¼ 4:5 at q=qn ¼ 0:01% in this study suggests that the irreversibility line has a strong temperature dependence in Ru-1222 system which could result in large thermally activated flux creep. It was also noted that the value of the exponent increases with increasing anisotropy of the system [9]. The c ¼ 4:5 in Ru-1222 system may imply that this system has a relatively high anisotropy. The resistivity data at low dissipation part (When magnetic fluxes move in the presence of current flow and magnetic field, energy dissipation or resistive behavior in high temperature super-
L. Shi et al. / Physica C 386 (2003) 65–68
qðT ; H Þ ¼ q0 ðH Þ expfU ðH Þ½1 T =Tc =kB T g
ρ (Ω .cm)
10T 8T 4T 2T 1T
1E-3
150
100
ð2Þ
Here U denotes the activation energy for flux creep and kB is the Boltzmann constant. The resistivity is logarithmically plotted against 1=T in Fig. 3, which shows that the curve at the low dissipation part is linear. The activation energy U is obtained from the slope of log q–1=T curves. The calculated activation energy U as a function of the applied magnetic field is plotted in Fig. 4. The U value is obviously smaller than those of other high temperature superconductors. This may be due to the coexistence of superconductivity and ferromagnetism in RuSr2 Gd1:4 Ce0:6 Cu2 O10d . The presence of ferromagnetic state might make the superconductivity more easily destroyed for RuSr2 Gd1:4 Ce0:6 Cu2 O10d . It is also found that the activation energy can be fitted by U ¼ 157H 0:59 , which is similar to the results for other high temperature superconductors [10,12] and agrees with the observation that the low dissipation part well below magnetoresistance transition temperature is dominated by a thermally activated flux flow model [10].
0.01
200
U (K)
conductors occurs [10,11]. The low value of magnetoresistance well below Tc results from weak magnetic flux creep in this temperature region where the energy dissipation is also low. This part of resistive curve well below Tc is usually called low dissipation part.) can be described by the Arrhenius thermal activation law
67
50
0
3
6
9
12
H (Tesla) Fig. 4. Field dependence of activation energy U. The solid line denotes the fitting results.
4. Conclusions The irreversibility line derived from the resistivity data is found to follow a power law c Hi ¼ að1 T =Tc Þ with c ¼ 4:5 at q=qn ¼ 0:01%, which may suggest that there is a giant flux creep due to thermal activation in Ru-1222 system. The activation energy U obtained from the low dissipation part of qðT Þ curves with the Arrhenius thermal activation law is obviously smaller than that of other high temperature superconductors, which may be due to the coexistence of superconductivity and ferromagnetism in RuSr2 Gd1:4 Ce0:6 Cu2 O10d .
Acknowledgements The work is supported by the National Natural Science Foundation and the Ministry of Science and Technology of China (NKBRSF-G19990646).
1E-4
References 0.0
0.1
0.2
0.3
1/T (K -1) Fig. 3. Plot of log q–1=T for RuSr2 Gd1:4 Ce0:6 Cu2 O10d at various magnetic fields.
[1] K.A. M€ uller, M. Takashige, J.G. Bednorz, Phys. Rev. Lett. 58 (1987) 1143. [2] I. Felner, U. Asaf, Y. Levi, O. Millo, Phys. Rev. B 55 (1997) 3374.
68
L. Shi et al. / Physica C 386 (2003) 65–68
[3] W.K. Yeoh, C.A. Kek, R. Abd-Shukor, Supercond. Sci. Tech. 15 (2002) 361. [4] L. Bauernfeind, W. Widder, H.F. Braun, Physica C 254 (1995) 151. [5] G.V.M. Williams, M. Ryan, Phys. Rev. B 64 (2001) 094515. [6] Y. Yeshrun, A.P. Malozemoff, Phys. Rev. Lett. 60 (1988) 2202. [7] Z.J. Huang, Y.Y. Xue, R.L. Meng, C.W. Chu, Phys. Rev. B 49 (1994) 4218.
[8] Y.W. Xu, M. Suenaga, Phys. Rev. B 43 (1991) 5516. [9] I.K. Gopalakrishnan, J.V. Yakhmi, Philos. Mag. B 75 (1997) 497. [10] B.A. Albiss, M.K. Hassan, M.A. Al-Akhras, I.A. AlOmari, A. Shariah, J. Shobaki, K.A. Azez, H. Ozkan, Physica C 331 (2000) 297. [11] S.K. Gupta, S. Sen, K.P. Muthe, J.C. Vyas, D.K. Aswal, M.R. Gonal, C.S. Viswanadham, G.L. Goswami, V.C. Sahni, Physica C 363 (2001) 140. [12] G.C. Kim, Y.C. Kim, Solid State Commun. 101 (1997) 173.
Irreversibility line in the superconductor RuSr2Gd1:4Ce0:6Cu2O10d L. Shi, S.J. Feng, G. Li, X.F. Sun, X.-G. Li
*
Structure Research Laboratory, Department of Materials Science and Engineering, University of Science and Technology of China, Hefei 230026, China
Abstract The resistive transition of the superconductor RuSr2 Gd1:4 Ce0:6 Cu2 O10d is measured under magnetic fields from 0 to 10 T. The results show that the irreversibility line determined from the different reduced resistivity criterion can be fitted well by the expression: Hi ¼ að1 T =Tc Þc . The activation energy (U ) is obtained from the low dissipation parts of the qðT Þ curves using the Arrhenius activation law qðT ; H Þ ¼ q0 ðH Þ expfU ðH Þ½1 T =Tc =kB T g. The U value obtained is smaller than that of other high temperature cuprate superconductors, which may be due to the coexistence of superconductivity and ferromagnetism in RuSr2 Gd1:4 Ce0:6 Cu2 O10d . It is also found that the activation energy can be fitted by U ¼ 157H 0:59 . Ó 2002 Elsevier Science B.V. All rights reserved. PACS: 74.60.Ge; 74.72.Jt; 74.25.Fy Keywords: Ru-1222; Irreversibility line; Flux creep
1. Introduction The irreversibility line, a novel feature that was first reported by M€ uller et al. [1] in the field-temperature phase diagram H ðT Þ of the Ba–La–Cu–O system, defines the boundary between reversible and irreversible regions. The irreversibility line is believed to be strongly dependent on the flux pinning property of the superconductors. The knowledge of this line is not only crucial to an understanding of the flux pinning properties but also important for potential applications of the high temperature superconductors. The recent
discovery of the coexistence of superconductivity and ferromagnetism in a hybrid ruthenate–cuprate RuSr2 Gd1:4 Ce0:6 Cu2 O10d (Ru-1222) with layered perovskite structure has attracted a great deal of interest in the properties of this material [2–5]. The Ru-1222 material exhibits ferromagnetic order at a rather high temperature, TM ¼ 180 K, and becomes superconductive at Tc ¼ 42 K, within the ferromagnetically ordered state [2]. In the present study, the irreversibility line for Ru-1222 is derived from resistance data at magnetic fields from 0 to 10 T and its pinning properties are also investigated. 2. Experimental
*
Corresponding author. Tel./fax: +86-551-3603408. E-mail address: [email protected] (X.-G. Li).
A polycrystalline sample of the RuSr2 Gd1:4 Ce0:6 Cu2 O10d was synthesized by a solid-state
0921-4534/02/$ - see front matter Ó 2002 Elsevier Science B.V. All rights reserved. doi:10.1016/S0921-4534(02)02148-2
L. Shi et al. / Physica C 386 (2003) 65–68
reaction method from a stoichiometric mixture of the powders RuO2 , SrCO3 , Gd2 O3 , CeO2 , and CuO. The mixture was thoroughly ground and diepressed into pellets before preliminary reaction in air at 1000 °C for 36 h. The resulting samples were reground, repelleted, and heated at 1070 °C in flowing oxygen for 60 h, and finally slowly cooled to room temperature. X-ray diffraction (XRD) patterns were measured with a Mac Science MXP18AHF X-ray diffractometer using Cu Ka radiation. The resistance of the samples was measured using a standard four-probe method down to 4.2 K. Magnetoresistance was measured in the magnetic fields of up to 10 T using an Oxford Instruments superconducting magnet.
12
ρ/ρn 20% 10% 0.5% 0.1% 0.01%
9
H (Tesla)
66
6
3
0 3
6
9
12
15
Tirr (K) Fig. 2. The Tirr vs. field H for RuSr2 Gd1:4 Ce0:6 Cu2 O10d at different reduced resistivity criterion. The solid lines denote the fitting results.
3. Results and discussion The powder XRD pattern recorded at room temperature for the sample RuSr2 Gd1:4 Ce0:6 Cu2 O10d reveals that it is nearly single-phase 1222. Fig. 1 shows the resistive transition for Ru-1222 in magnetic fields of up to 10 T. In zero field, the onset superconducting transition temperature TcðonsetÞ and zero resistivity temperature Tcð0Þ are 45 and 16 K, respectively. The resistivity curves broaden gradually, and both Tcð0Þ and TcðonsetÞ decrease with the increasing magnetic field. In Fig. 2, the magnetic field values (H ) are plotted as function of the corresponding irreversibility tempera-
ρ (Ω .cm)
0.02
10T 8T 4T 2T 1T 0T
0.01
0.00
0
20
40
60
T (K) Fig. 1. The temperature dependence of the resistivity for RuSr2 Gd1:4 Ce0:6 Cu2 O10d at various magnetic fields.
tures (Tirr ) which are defined at 0.01%, 0.1%, 0.5%, 10%, 20% of the normal state resistivity (qn ), respectively. We can see that the irreversibility line shifts to lower temperatures with decrease of q=qn It is found that the H –Tirr curves in Fig. 2 can all be fitted well by expression Hi ¼ að1 T =Tc Þc
ð1Þ
where a and c are fitting parameters. The c value is found to increase with decreasing q=qn from 1.3 at q=qn ¼ 20% to 4.5 at q=qn ¼ 0:01%. This power dependence law was also observed in other high temperature superconductors where the exponent c has values ranging from 1.5 to 5.5 for various high Tc families, e.g.: c ¼ 1:5 for YBa2 Cu3 O7 [6]; 2.5 for HgBa2 CaCu2 O6þd [7]; 5.5 for Bi2 Sr2 CaCu2 O8 [8]. The relative large value of c ¼ 4:5 at q=qn ¼ 0:01% in this study suggests that the irreversibility line has a strong temperature dependence in Ru-1222 system which could result in large thermally activated flux creep. It was also noted that the value of the exponent increases with increasing anisotropy of the system [9]. The c ¼ 4:5 in Ru-1222 system may imply that this system has a relatively high anisotropy. The resistivity data at low dissipation part (When magnetic fluxes move in the presence of current flow and magnetic field, energy dissipation or resistive behavior in high temperature super-
L. Shi et al. / Physica C 386 (2003) 65–68
qðT ; H Þ ¼ q0 ðH Þ expfU ðH Þ½1 T =Tc =kB T g
ρ (Ω .cm)
10T 8T 4T 2T 1T
1E-3
150
100
ð2Þ
Here U denotes the activation energy for flux creep and kB is the Boltzmann constant. The resistivity is logarithmically plotted against 1=T in Fig. 3, which shows that the curve at the low dissipation part is linear. The activation energy U is obtained from the slope of log q–1=T curves. The calculated activation energy U as a function of the applied magnetic field is plotted in Fig. 4. The U value is obviously smaller than those of other high temperature superconductors. This may be due to the coexistence of superconductivity and ferromagnetism in RuSr2 Gd1:4 Ce0:6 Cu2 O10d . The presence of ferromagnetic state might make the superconductivity more easily destroyed for RuSr2 Gd1:4 Ce0:6 Cu2 O10d . It is also found that the activation energy can be fitted by U ¼ 157H 0:59 , which is similar to the results for other high temperature superconductors [10,12] and agrees with the observation that the low dissipation part well below magnetoresistance transition temperature is dominated by a thermally activated flux flow model [10].
0.01
200
U (K)
conductors occurs [10,11]. The low value of magnetoresistance well below Tc results from weak magnetic flux creep in this temperature region where the energy dissipation is also low. This part of resistive curve well below Tc is usually called low dissipation part.) can be described by the Arrhenius thermal activation law
67
50
0
3
6
9
12
H (Tesla) Fig. 4. Field dependence of activation energy U. The solid line denotes the fitting results.
4. Conclusions The irreversibility line derived from the resistivity data is found to follow a power law c Hi ¼ að1 T =Tc Þ with c ¼ 4:5 at q=qn ¼ 0:01%, which may suggest that there is a giant flux creep due to thermal activation in Ru-1222 system. The activation energy U obtained from the low dissipation part of qðT Þ curves with the Arrhenius thermal activation law is obviously smaller than that of other high temperature superconductors, which may be due to the coexistence of superconductivity and ferromagnetism in RuSr2 Gd1:4 Ce0:6 Cu2 O10d .
Acknowledgements The work is supported by the National Natural Science Foundation and the Ministry of Science and Technology of China (NKBRSF-G19990646).
1E-4
References 0.0
0.1
0.2
0.3
1/T (K -1) Fig. 3. Plot of log q–1=T for RuSr2 Gd1:4 Ce0:6 Cu2 O10d at various magnetic fields.
[1] K.A. M€ uller, M. Takashige, J.G. Bednorz, Phys. Rev. Lett. 58 (1987) 1143. [2] I. Felner, U. Asaf, Y. Levi, O. Millo, Phys. Rev. B 55 (1997) 3374.
68
L. Shi et al. / Physica C 386 (2003) 65–68
[3] W.K. Yeoh, C.A. Kek, R. Abd-Shukor, Supercond. Sci. Tech. 15 (2002) 361. [4] L. Bauernfeind, W. Widder, H.F. Braun, Physica C 254 (1995) 151. [5] G.V.M. Williams, M. Ryan, Phys. Rev. B 64 (2001) 094515. [6] Y. Yeshrun, A.P. Malozemoff, Phys. Rev. Lett. 60 (1988) 2202. [7] Z.J. Huang, Y.Y. Xue, R.L. Meng, C.W. Chu, Phys. Rev. B 49 (1994) 4218.
[8] Y.W. Xu, M. Suenaga, Phys. Rev. B 43 (1991) 5516. [9] I.K. Gopalakrishnan, J.V. Yakhmi, Philos. Mag. B 75 (1997) 497. [10] B.A. Albiss, M.K. Hassan, M.A. Al-Akhras, I.A. AlOmari, A. Shariah, J. Shobaki, K.A. Azez, H. Ozkan, Physica C 331 (2000) 297. [11] S.K. Gupta, S. Sen, K.P. Muthe, J.C. Vyas, D.K. Aswal, M.R. Gonal, C.S. Viswanadham, G.L. Goswami, V.C. Sahni, Physica C 363 (2001) 140. [12] G.C. Kim, Y.C. Kim, Solid State Commun. 101 (1997) 173.