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Second peak effect in SmBa2Cu3Oy
Physica C 386 (2003) 73–76 www.elsevier.com/locate/physc
Second peak effect in SmBa2Cu3Oy S.Y. Ding a,*, X. Leng a, H. Luo a, Y. Liu a, L. Xiao b, H.T. Reng b, Y.L. Jiao b, M.H. Zheng b b
a Department of Physics, National Laboratory of Solid State Microstructures, Nanjing University, Nanjing 210093, PR China Superconducting Materials Research Institute Center, Beijing General Institute for Non-ferrous Metals, Beijing 100088, PR China
Abstract Two SmBa2 Cu3 Oy samples with Y211 (Sm1 and Sm2) were fabricated by the melt-textured growth method to study the effect of heat treatment and argon atmosphere on the second peak effect (SP). Magnetization–temperature (M–T ) measurement at 10 G field cooling shows that the sample Sm1 has a transition temperature Tc ¼ 80 K but the Sm2 has higher Tc ( ¼ 90 K) and higher irreversibility fields than Sm1. Magnetization versus field (M–B curves) at various temperatures T in fields up to 7 T was measured. The SP of the two samples was observed and compared over a range of temperatures. Discussion of flux pinning and the effect of Ar and 211 is made. Ó 2002 Published by Elsevier Science B.V. PACS: 74.62.Bf; 74.60.)w Keywords: Critical current; Ar and 211 doping; Melt-textured growth-SBCO
1. Introduction A number of authors have contributed to the so-called second peak effect (SP) in either the jc –T or the jc –H relationships for variety of superconducting samples. SP is also called the ‘‘fishtail effect’’ [1], the ‘‘dip effect’’ [2] or other names, according to recent reviews as for example, Ref. [1]. The physics underlying SP is very complicated and no one model can satisfactorily explain all the experimental observations [1]. Therefore, it is still an interesting subject to study. Moreover, SP may be accompanied by a memory phenomenon [3] or
*
Corresponding author. Tel.: +86-25-359-3661; fax: +86-25359-5535. E-mail address: [email protected] (S.Y. Ding).
history effect, [4] which shows SP can occur for either an ordered or disordered flux line lattice [3]. In this paper, we report our experimental study on the relationship between the irreversibility field and SP. The melt-textured growth (MTG) SmBa2 Cu3 Oy (SBCO) samples were fabricated and different heat treatment procedures in Ar or O2 with different pressures were conducted to vary the reversible such as Tc and irreversible superconducting properties.
2. Experimental SBCO bulks of coin-like cylinders with diameter 10 mm and nominal composition SmBa2 Cu3 Oy þ 40 mol% Y2 BaCuO5 were fabricated by the MTG method, whose. Two samples (Sm1 and
0921-4534/02/$ - see front matter Ó 2002 Published by Elsevier Science B.V. doi:10.1016/S0921-4534(02)02219-0
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S.Y. Ding et al. / Physica C 386 (2003) 73–76
Sm2) of flat quasi-crystals were prepared by the splitting along the cleavage plane of single domain SBCO bulks, with a single domain. A 60 h/350 °C post annealing for Sm1 and Sm2 was conducted in an oxygen atmosphere at a pressure of 10 atm, to study the effect of heat treatment on the SP. However, a 60 h/950 °C heat treatment was conducted in an argon atmosphere at a pressure of 1 atm before the oxygen annealing was conducted, to study the influence of oxygen content on SP. Sizes of both the samples are around 4 mm in diameter with 0.35 mm thick. The c-axis is perpendicular to the wider surfaces. Magnetization– temperature (M–T ) measurement at 10 G field cooling (FC) shows that the sample Sm1 has transition temperature Tc ¼ 76 K but the Sm2 has higher Tc ( ¼ 90 K) and higher irreversibility field than Sm1. Magnetization–field hysteresis loops (M–B curves) at various temperatures T in fields up to 7 T were measured for the samples. The field sweeping rate of dB=dt ¼ 0:4 T/min was used for all the loops. The SP of the two samples was observed and compared over a range of temperatures. Discussion is made of flux pinning and the effect of Ar and 211.
Fig. 1. Hysteric magnetization loops. The low field peak of magnetization (the first peak, FP) is clear as routinely observed for both the samples. Note that first peak of SM1 (FM1) is smaller than FM2.
3. Results and discussion The M–T curve measured by vibrating sample magnetometer (VSM) at 10 G FC for the two samples shows that the so-called zero resistance transition temperature is TCO 71 K for Sm1 and TCO 80 K for Sm2. Fig. 1 displays the hysteresis loops at 77 K. It is clearly seen that a first magnetization peak (FP1 and FP2) appears at very low applied field B each loop for the two samples, although the magnitude of M including the height of Sm1 is smaller than that of Sm2 (FP1 < FP2). With descending temperature, M and its loops increases as usual. Fig. 2 shows the hysteresis loops at 50 K for the two samples. Two things are clearly seen, (i) the second peak (SP2) on M–H curves adjacent to irreversibility field Hirr is developed for sample Sm2 although it is very flat and small, (ii) the FP1 is now higher than that of Sm2 (FP1 > FP2) and a second peak of Sm1 (SP1) has developed and it grows so quick that its height is
Fig. 2. Hysteric magnetization loops. The loop of SM2 grows slower than that of SM1. However, SP2 has developed and grows faster than FM1.
larger than that of FPL shown in Fig. 3 are the loops of the samples at 20 K, where the tendency for height of FP1 to increase faster than that of SP1 with temperature results in the height of FP1 being larger than that of Sm1 (FP1 > SP1). Hence one can say that when 50 > T > 20 K, FP1 increase faster than SP1, in contrast to the case at T > 50 K. These data tell us interesting information. First, in spite of their difference in superconducting parameters (Tc , Hirr , critical current density Jc , etc.)
S.Y. Ding et al. / Physica C 386 (2003) 73–76
Fig. 3. Hysteric magnetization loops at 20 K. It is noted that SP1 grows so slower that FM1 now is higher than SP1.
there exist two magnetization peaks for both the samples, indicating the SP is not a special but very basic property at least for oxide high Tc superconductors. Secondly, the magnetization loop and thus flux the pinning strength of Sm1 increases faster than that those of the later with descending temperature in spite of Tc and Hirr of SM1 is lower than the later. This fact implies that SP1 of the sample with stronger flux pinning is more pronounced than that of with weaker pinning. Thirdly, the height of SP2 is always lower than FP2 whereas the height of FP1 is larger than SP1 at high or low temperatures (say T P 60 K, or T 6 20 K) and vice versa in the intermediate temperatures (say 50 > T > 30 K). Hence it is reasonable to consider a different mechanisms as the cause of SP. It was suggested that the first peak FP in M–H curve was caused by surface barriers, such as the geometric barriers (GB) and the BLB (Bean–Livingston barrier) [5,6]. Experiments including the local-Hall-array magnetometer [5] and magnetooptics observation [7], support this explanation. The temperature dependence of GB and BLB is roughly the same as Hc1 –T , which is proportional to 1 T =Tc at T is not very low, where Hc1 is lower critical field, resulting in MFPM (the height of FP) decreases as 1 T =Tc with decreasing temperature. It is widely accepted that SP is caused by bulk pinning (BP), see, e.g. [2,5,7]. However, the temperature dependence of BP, which gives raise
75
the temperature dependence of the height of FP, MSPM –T , is rather complicated. As long as T > Tirr no BP occurs and thus one can assumes y that MFPM scales as ð1 T =Tirr Þ , i.e. MSPM / ½1 y T =Tirr , where Tirr is the irreversibility temperature and is significantly lower than Tc , in contrast with the temperature dependence, MFPM –T . This understanding can explain the experimental temperature dependence of MSPM if y > x at higher temperatures. Nevertheless, in the still lower temperature (T < 30 K for SM1) the BP ðMSPM Þ increases slower than SP ðMFPM Þ, implies that there might be a new mechanism affecting vortex pinning. We propose that quantum fluctuation at low temperatures became more important, which weaken BP but no influence on SP. The present experiment shows that the post heat treatment in argon gas enlarges the hysteresis magnetization loop, and thus strengthens the bulk flux pinning. The mechanism is worthy to study further. In summary, we have prepared two SmBa2 Cu3 O7d samples, which were annealed with and without argon atmosphere, respectively. By means of measurements of dc magnetization hysteric loop, the second peak effect was observed for both the samples. The sample annealed in Ar has lower transition temperature and irreversibility field but stronger flux pinning effect and pronounced second peak, indicating that it is not necessary for a pronounced second peak effect to take place in weaker bulk pinning system. The present experiment shows that the irreversibility field Hirr cannot be considered as a parameter characterizing flux pinning strength of a superconductor because the loop of SM1 with smaller Hirr is larger than that of SM2 with higher Hirr . Acknowledgements The Ministry of Science and Technology of China (Gl 999064602) and NNSFC supported this work under contract no. 19994016. References [1] M. Werner, F.M. Sauerzopf, H.W. Weber, Phys. Rev. B 61 (2000) 14795.
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S.Y. Ding et al. / Physica C 386 (2003) 73–76
[2] P. Zhang, S.Y. Ding, X.F. Wu, L. Qiu, Z.H. Wang, C. Ren, S.A. Aruna, X.X. Yao, J. Shi, Phys. Rev. B 62 (2000) 5374. [3] Y. Paltiel, E. Zeldov, Y.N. Myasoedov, H. Shtrikman, S. Bhattacharya, M.J. Higgins, Z.L. Xiao, E.Y. Andrei, P.L. Gammel, Bishop, Nature 403 (2000) 398. [4] X.F. Wu, H. Luo, H.M. Luo, Y. Liu, T. Yang, X. Leng, L. Qiu, S.Y. Ding, Supercond. Sci. Technol. 15 (2002) 385.
[5] E. Zeldov, A.I. Larkin, V.B. Geshkenbien, M. Konczykowsky, D. Majer, B. Khaykovich, V.M. Vinokur, Shtrikman, Phys. Rev. Lett. 73 (1994) 1428. [6] C.P. Bean, J.D. Linvingston, Phys. Rev. Lett. 12 (1994) 14. [7] C.J. Van der Beek, S. Calson, M.N. Imdenbom, M. Konczykowsky, Phys. Rev. Lett. 84 (1994) 4196.
Second peak effect in SmBa2Cu3Oy S.Y. Ding a,*, X. Leng a, H. Luo a, Y. Liu a, L. Xiao b, H.T. Reng b, Y.L. Jiao b, M.H. Zheng b b
a Department of Physics, National Laboratory of Solid State Microstructures, Nanjing University, Nanjing 210093, PR China Superconducting Materials Research Institute Center, Beijing General Institute for Non-ferrous Metals, Beijing 100088, PR China
Abstract Two SmBa2 Cu3 Oy samples with Y211 (Sm1 and Sm2) were fabricated by the melt-textured growth method to study the effect of heat treatment and argon atmosphere on the second peak effect (SP). Magnetization–temperature (M–T ) measurement at 10 G field cooling shows that the sample Sm1 has a transition temperature Tc ¼ 80 K but the Sm2 has higher Tc ( ¼ 90 K) and higher irreversibility fields than Sm1. Magnetization versus field (M–B curves) at various temperatures T in fields up to 7 T was measured. The SP of the two samples was observed and compared over a range of temperatures. Discussion of flux pinning and the effect of Ar and 211 is made. Ó 2002 Published by Elsevier Science B.V. PACS: 74.62.Bf; 74.60.)w Keywords: Critical current; Ar and 211 doping; Melt-textured growth-SBCO
1. Introduction A number of authors have contributed to the so-called second peak effect (SP) in either the jc –T or the jc –H relationships for variety of superconducting samples. SP is also called the ‘‘fishtail effect’’ [1], the ‘‘dip effect’’ [2] or other names, according to recent reviews as for example, Ref. [1]. The physics underlying SP is very complicated and no one model can satisfactorily explain all the experimental observations [1]. Therefore, it is still an interesting subject to study. Moreover, SP may be accompanied by a memory phenomenon [3] or
*
Corresponding author. Tel.: +86-25-359-3661; fax: +86-25359-5535. E-mail address: [email protected] (S.Y. Ding).
history effect, [4] which shows SP can occur for either an ordered or disordered flux line lattice [3]. In this paper, we report our experimental study on the relationship between the irreversibility field and SP. The melt-textured growth (MTG) SmBa2 Cu3 Oy (SBCO) samples were fabricated and different heat treatment procedures in Ar or O2 with different pressures were conducted to vary the reversible such as Tc and irreversible superconducting properties.
2. Experimental SBCO bulks of coin-like cylinders with diameter 10 mm and nominal composition SmBa2 Cu3 Oy þ 40 mol% Y2 BaCuO5 were fabricated by the MTG method, whose. Two samples (Sm1 and
0921-4534/02/$ - see front matter Ó 2002 Published by Elsevier Science B.V. doi:10.1016/S0921-4534(02)02219-0
74
S.Y. Ding et al. / Physica C 386 (2003) 73–76
Sm2) of flat quasi-crystals were prepared by the splitting along the cleavage plane of single domain SBCO bulks, with a single domain. A 60 h/350 °C post annealing for Sm1 and Sm2 was conducted in an oxygen atmosphere at a pressure of 10 atm, to study the effect of heat treatment on the SP. However, a 60 h/950 °C heat treatment was conducted in an argon atmosphere at a pressure of 1 atm before the oxygen annealing was conducted, to study the influence of oxygen content on SP. Sizes of both the samples are around 4 mm in diameter with 0.35 mm thick. The c-axis is perpendicular to the wider surfaces. Magnetization– temperature (M–T ) measurement at 10 G field cooling (FC) shows that the sample Sm1 has transition temperature Tc ¼ 76 K but the Sm2 has higher Tc ( ¼ 90 K) and higher irreversibility field than Sm1. Magnetization–field hysteresis loops (M–B curves) at various temperatures T in fields up to 7 T were measured for the samples. The field sweeping rate of dB=dt ¼ 0:4 T/min was used for all the loops. The SP of the two samples was observed and compared over a range of temperatures. Discussion is made of flux pinning and the effect of Ar and 211.
Fig. 1. Hysteric magnetization loops. The low field peak of magnetization (the first peak, FP) is clear as routinely observed for both the samples. Note that first peak of SM1 (FM1) is smaller than FM2.
3. Results and discussion The M–T curve measured by vibrating sample magnetometer (VSM) at 10 G FC for the two samples shows that the so-called zero resistance transition temperature is TCO 71 K for Sm1 and TCO 80 K for Sm2. Fig. 1 displays the hysteresis loops at 77 K. It is clearly seen that a first magnetization peak (FP1 and FP2) appears at very low applied field B each loop for the two samples, although the magnitude of M including the height of Sm1 is smaller than that of Sm2 (FP1 < FP2). With descending temperature, M and its loops increases as usual. Fig. 2 shows the hysteresis loops at 50 K for the two samples. Two things are clearly seen, (i) the second peak (SP2) on M–H curves adjacent to irreversibility field Hirr is developed for sample Sm2 although it is very flat and small, (ii) the FP1 is now higher than that of Sm2 (FP1 > FP2) and a second peak of Sm1 (SP1) has developed and it grows so quick that its height is
Fig. 2. Hysteric magnetization loops. The loop of SM2 grows slower than that of SM1. However, SP2 has developed and grows faster than FM1.
larger than that of FPL shown in Fig. 3 are the loops of the samples at 20 K, where the tendency for height of FP1 to increase faster than that of SP1 with temperature results in the height of FP1 being larger than that of Sm1 (FP1 > SP1). Hence one can say that when 50 > T > 20 K, FP1 increase faster than SP1, in contrast to the case at T > 50 K. These data tell us interesting information. First, in spite of their difference in superconducting parameters (Tc , Hirr , critical current density Jc , etc.)
S.Y. Ding et al. / Physica C 386 (2003) 73–76
Fig. 3. Hysteric magnetization loops at 20 K. It is noted that SP1 grows so slower that FM1 now is higher than SP1.
there exist two magnetization peaks for both the samples, indicating the SP is not a special but very basic property at least for oxide high Tc superconductors. Secondly, the magnetization loop and thus flux the pinning strength of Sm1 increases faster than that those of the later with descending temperature in spite of Tc and Hirr of SM1 is lower than the later. This fact implies that SP1 of the sample with stronger flux pinning is more pronounced than that of with weaker pinning. Thirdly, the height of SP2 is always lower than FP2 whereas the height of FP1 is larger than SP1 at high or low temperatures (say T P 60 K, or T 6 20 K) and vice versa in the intermediate temperatures (say 50 > T > 30 K). Hence it is reasonable to consider a different mechanisms as the cause of SP. It was suggested that the first peak FP in M–H curve was caused by surface barriers, such as the geometric barriers (GB) and the BLB (Bean–Livingston barrier) [5,6]. Experiments including the local-Hall-array magnetometer [5] and magnetooptics observation [7], support this explanation. The temperature dependence of GB and BLB is roughly the same as Hc1 –T , which is proportional to 1 T =Tc at T is not very low, where Hc1 is lower critical field, resulting in MFPM (the height of FP) decreases as 1 T =Tc with decreasing temperature. It is widely accepted that SP is caused by bulk pinning (BP), see, e.g. [2,5,7]. However, the temperature dependence of BP, which gives raise
75
the temperature dependence of the height of FP, MSPM –T , is rather complicated. As long as T > Tirr no BP occurs and thus one can assumes y that MFPM scales as ð1 T =Tirr Þ , i.e. MSPM / ½1 y T =Tirr , where Tirr is the irreversibility temperature and is significantly lower than Tc , in contrast with the temperature dependence, MFPM –T . This understanding can explain the experimental temperature dependence of MSPM if y > x at higher temperatures. Nevertheless, in the still lower temperature (T < 30 K for SM1) the BP ðMSPM Þ increases slower than SP ðMFPM Þ, implies that there might be a new mechanism affecting vortex pinning. We propose that quantum fluctuation at low temperatures became more important, which weaken BP but no influence on SP. The present experiment shows that the post heat treatment in argon gas enlarges the hysteresis magnetization loop, and thus strengthens the bulk flux pinning. The mechanism is worthy to study further. In summary, we have prepared two SmBa2 Cu3 O7d samples, which were annealed with and without argon atmosphere, respectively. By means of measurements of dc magnetization hysteric loop, the second peak effect was observed for both the samples. The sample annealed in Ar has lower transition temperature and irreversibility field but stronger flux pinning effect and pronounced second peak, indicating that it is not necessary for a pronounced second peak effect to take place in weaker bulk pinning system. The present experiment shows that the irreversibility field Hirr cannot be considered as a parameter characterizing flux pinning strength of a superconductor because the loop of SM1 with smaller Hirr is larger than that of SM2 with higher Hirr . Acknowledgements The Ministry of Science and Technology of China (Gl 999064602) and NNSFC supported this work under contract no. 19994016. References [1] M. Werner, F.M. Sauerzopf, H.W. Weber, Phys. Rev. B 61 (2000) 14795.
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S.Y. Ding et al. / Physica C 386 (2003) 73–76
[2] P. Zhang, S.Y. Ding, X.F. Wu, L. Qiu, Z.H. Wang, C. Ren, S.A. Aruna, X.X. Yao, J. Shi, Phys. Rev. B 62 (2000) 5374. [3] Y. Paltiel, E. Zeldov, Y.N. Myasoedov, H. Shtrikman, S. Bhattacharya, M.J. Higgins, Z.L. Xiao, E.Y. Andrei, P.L. Gammel, Bishop, Nature 403 (2000) 398. [4] X.F. Wu, H. Luo, H.M. Luo, Y. Liu, T. Yang, X. Leng, L. Qiu, S.Y. Ding, Supercond. Sci. Technol. 15 (2002) 385.
[5] E. Zeldov, A.I. Larkin, V.B. Geshkenbien, M. Konczykowsky, D. Majer, B. Khaykovich, V.M. Vinokur, Shtrikman, Phys. Rev. Lett. 73 (1994) 1428. [6] C.P. Bean, J.D. Linvingston, Phys. Rev. Lett. 12 (1994) 14. [7] C.J. Van der Beek, S. Calson, M.N. Imdenbom, M. Konczykowsky, Phys. Rev. Lett. 84 (1994) 4196.