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Pinning properties of melt-textured Dy123 superconductors with Dy211 in various particle sizes
Physica C 378–381 (2002) 755–758 www.elsevier.com/locate/physc
Pinning properties of melt-textured Dy123 superconductors with Dy211 in various particle sizes K. Inoue *, S. Nariki, M. Murakami Superconductivity Research Laboratory, ISTEC, 1-16-25 Shibaura, Minato-ku, Tokyo 105-0023, Japan Received 27 September 2001; accepted 20 December 2001
Abstract We have investigated the effect of Dy2 BaCuO5 (Dy211) particle size on the pinning properties of DyBa2 Cu3 O7d by measuring the dc magnetization and the ac susceptibility. The suppression in the normalized relaxation rate (S) occurs with reducing the Dy211 particle size. The field-induced pinning is also effective in suppressing the flux creep in the intermediate filed region. The irreversibility line was located in a higher temperature and field region for the sample with the smaller Dy211 particles. Ó 2002 Elsevier Science B.V. All rights reserved. PACS: 74.60.Ge; 74.60.Jg Keywords: Critical current density; Magnetic relaxation; Irreversibility line; Interfacial pinning; Dy123
1. Introduction Melt-textured REBa2 Cu3 O7d (RE: rare earth element) superconductors exhibit high critical current density (Jc ) even in a high field and temperature region [1–3]. Large grain REBa2 Cu3 O7d (RE123) bulk superconductors are also known to trap high magnetic field, which is attractive for various industrial applications. The trapped field can be enhanced by increasing Jc values. It is generally accepted that an addition of RE2 BaCuO5 (RE211) contributes to an improvement of Jc and thus an enhancement of the trapped field. Either an increase in the volume fraction or the refinement of RE211 particles leads to an improvement of pin-
ning through an increase of RE123/RE211 interfacial area [1–3]. Recently, it was reported that melt-textured DyBa2 Cu3 O7d (Dy123) could trap higher magnetic field than Y123, in that a refinement of Dy2 BaCuO5 (Dy211) particles was effective in increasing Jc and trapped field [4]. Hence, Dy123 has significant potential for high field applications. In the present study, we have investigated the size effect of the Dy211 particle on the pinning properties of Dy123 by measuring the dc magnetization and the ac susceptibility. We focus on the suppression of magnetic relaxation and the enhancement of the irreversibility field with reducing Dy211 particle size. 2. Experimental
*
Corresponding author. Tel.: +81-3-3454-9284; fax: +81-33454-9287. E-mail address: [email protected] (K. Inoue).
Dy211 was prepared from commercial Dy2 O3 , BaO2 , and CuO powders. The powders were
0921-4534/02/$ - see front matter Ó 2002 Elsevier Science B.V. All rights reserved. PII: S 0 9 2 1 - 4 5 3 4 ( 0 2 ) 0 1 5 3 7 - X
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K. Inoue et al. / Physica C 378–381 (2002) 755–758
Table 1 Sample dimension, critical temperature (Tc ) and the average diameter of Dy211 (d) Sample name
Sample dimension (mm)
Tc (K)
d ðlm)
A B C
0:9 1:1 0:5 1:3 1:4 0:5 1:2 1:4 0:5
90.4 89.9 90.7
0.63 0.75 0.85
The c-axis is parallel to the shortest axis.
calcined at different temperatures to control the grain size of Dy211. Dy211 powders in various particle sizes were added to commercial Dy123 powders in 40 mol% and thoroughly mixed. The precursor Dy123/Dy211 powders were pressed into pellets and then melt-processed in air, the details of which are described in Ref. [4]. The average diameter of Dy211 (d) in the melt-textured samples was analyzed with a scanning electron microscope (SEM) [4]. The sample dimension, the critical temperature (Tc ) and the average diameter of Dy211 are listed in Table 1. Dc magnetization measurements were carried out with a Quantum Design MPMS-XL SQUID magnetometer. Ac susceptibility measurements were performed with a Lakeshore 7229 ac susceptometer. In all the magnetic measurements, the magnetic field was applied parallel to the c-axis.
3. Results and discussion Fig. 1 shows the magnetic field dependence of Jc at the reduced temperature T =Tc ¼ 0:83 for three samples. One can see that the Jc is enhanced with the refinement of Dy211 particles in a low field. In the intermediate field region between 1 and 3 T, the shoulder-like secondary peak effect is observed in all the samples, in that Jc is the highest in the sample C with the largest Dy211 particle size due to an enhanced secondary peak effect. It is generally accepted that the secondary peak effect in the Dy123 system is mainly attributed to the field-induced pinning caused by the oxygen deficient clusters, since there is no Dy–Ba solid solution [5]. It is known that the amount of oxygen defects is reduced by the refinement of Dy211 particles, since the Dy211/Dy123 interfaces promote oxygen diffusion. When the magnetic field is increased above 3 T,
Fig. 1. Magnetic field dependence of Jc at the reduced temperature T =Tc ¼ 0:83 for three samples.
the Jc is again higher for the samples with smaller Dy211 particles as shown in the inset of Fig. 1. Fig. 2 shows the magnetic relaxation at 0.25 T and T =Tc ¼ 0:83 for three samples. We started to acquire the data at t ¼ 50 s. One can see the tendency that the magnetic relaxation is slower for the samples with smaller Dy211 particles. This suggests that the Dy123/Dy211 interfacial pinning is effective for the suppression in the flux creep in a relatively low field. We estimated the normalized relaxation rate (S) from the slope of the normalized M–ln t plot in the time window of 1000 < t < 3700 s. Fig. 3 shows the magnetic field dependence of S at T =Tc ¼ 0:83
Fig. 2. Magnetic relaxation at 0.25 T at T =Tc ¼ 0:83 for three samples.
K. Inoue et al. / Physica C 378–381 (2002) 755–758
Fig. 3. Magnetic field dependence of S at T =Tc ¼ 0:83 for three samples.
for three samples. The relaxation rate S is smaller for the sample with the smaller Dy211 particle in a relatively low field, as shown in the inset of Fig. 3. However, the S is the smallest for the sample C with the largest Dy211 particle in an intermediate field. A further increase of the magnetic field again leads to the smaller S for the sample with the smaller Dy211 particles. This suggests that the Dy123/Dy211 interfacial pinning is effective for the suppression in the flux creep up to the high field. In the intermediate field, the decrease in S for the sample with the larger Dy211 particle is ascribed to the field-induced pinning caused by the oxygen deficient clusters. The suppression of the flux creep due to the field-induced pinning is remarkable in this field region, although the interfacial pinning is also active. In a high field region, the suppression of the flux creep due to the interfacial pinning becomes again dominant. Similar suppression effects of relaxation due to the interfacial pinning and the field-induced pinning were also observed in the Nd123 system [6]. Fig. 4 shows the reduced temperature dependence of the irreversibility field (Hirr ). We defined the irreversibility field as the field where Jc ¼ 106 A/m2 . The irreversibility line is enhanced for the sample with the smaller Dy211 particle. This evidences that the Dy123/Dy211 interfacial pinning is active even in the vicinity of the irreversibility line. This result is similar to that of the Nd123 [3] and Y123 system [7].
757
Fig. 4. Temperature dependence of the irreversibility field (Hirr ) determined from the dc magnetization on a reduced temperature scale.
Fig. 5 shows the temperature dependence of the ac susceptibility at the dc field of 8.5 T at 125 Hz for three samples in a reduced temperature scale. The peak of the imaginary part (v00 ) occurs when the ac field penetrates to the center of a sample. The complete Kim model predicts the relation Jc ¼ 0:75hac =a at the peak position of v00 [8], where 2a is the sample thickness and hac is the ac field amplitude. We selected hac to hold the relation Jc ¼ 106 A/m2 and defined the irreversibility temperature (Tirr ) as the peak temperature of v00 .
Fig. 5. Temperature dependence of the ac susceptibility at the dc field of 8.5 T at 125 Hz for three samples on a reduced temperature scale.
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K. Inoue et al. / Physica C 378–381 (2002) 755–758
low and high field region. The suppression in the flux creep occurred with reducing the Dy211 particle size. The field-induced pinning also contributed to the suppression of relaxation in an intermediate filed region. The irreversibility line was enhanced for the sample with the smaller Dy211 particle. This evidences that the Dy123/Dy211 interfacial pinning is active even in the vicinity of the irreversibility field.
Acknowledgements Fig. 6. Temperature dependence of the irreversibility field (Hirr ) determined from the ac susceptibility on a reduced temperature scale.
Fig. 6 shows the reduced temperature dependence of the Hirr determined from the ac susceptibility. The irreversibility line is enhanced with reducing the Dy211 particle. This is consistent with the result of dc magnetization. The electric field is 104 V/m in the case of the ac susceptibility, while it is 108 V/m in the case of the dc magnetization. This suggests that the Dy123/ Dy211 interfacial pinning is effective in the vicinity of the irreversibility line on the wide range of the electric field.
4. Summary We have investigated the size effect of Dy211 particle on the pinning properties of Dy123/Dy211 composites by measuring the dc magnetization and the ac susceptibility. The Jc was enhanced with reducing the Dy211 particle size, particularly in a
This work was supported by the New Energy and Industrial Technology Development Organization (NEDO) as Collaborative Research and Development of Fundamental Technologies for Superconductivity Applications.
References [1] M. Murakami, K. Yamaguchi, H. Fujimoto, N. Nakamura, T. Taguchi, N. Koshizuka, S. Tanaka, Cryogenics 32 (1992) 930. [2] S. Nariki, S.J. Seo, N. Sakai, M. Murakami, Supercond. Sci. Tech. 13 (2000) 778. [3] T. Mochida, N. Chikumoto, M. Murakami, Phys. Rev. B 62 (2000) 1350. [4] S. Nariki, N. Sakai, M. Murakami, Physica C 357–360 (2001) 814. [5] S. Nariki, M. Murakami, Supercond. Sci. Tech. 15 (2002) 786. [6] T. Mochida, N. Chikumoto, M. Murakami, Phys. Rev. B 64 (2001) 064518. [7] D. Yoshimi, M. Migita, E.S. Otabe, T. Matsushita, Physica C 357–360 (2001) 590. [8] T. Ishida, R.B. Goldfarb, S. Okayasu, Y. Kazumata, J. Franz, T. Arndt, W. Schauer, Materials Science Forum, Trans Tech Publications Ltd, Switzerland, 1993, pp. 137– 139.
Pinning properties of melt-textured Dy123 superconductors with Dy211 in various particle sizes K. Inoue *, S. Nariki, M. Murakami Superconductivity Research Laboratory, ISTEC, 1-16-25 Shibaura, Minato-ku, Tokyo 105-0023, Japan Received 27 September 2001; accepted 20 December 2001
Abstract We have investigated the effect of Dy2 BaCuO5 (Dy211) particle size on the pinning properties of DyBa2 Cu3 O7d by measuring the dc magnetization and the ac susceptibility. The suppression in the normalized relaxation rate (S) occurs with reducing the Dy211 particle size. The field-induced pinning is also effective in suppressing the flux creep in the intermediate filed region. The irreversibility line was located in a higher temperature and field region for the sample with the smaller Dy211 particles. Ó 2002 Elsevier Science B.V. All rights reserved. PACS: 74.60.Ge; 74.60.Jg Keywords: Critical current density; Magnetic relaxation; Irreversibility line; Interfacial pinning; Dy123
1. Introduction Melt-textured REBa2 Cu3 O7d (RE: rare earth element) superconductors exhibit high critical current density (Jc ) even in a high field and temperature region [1–3]. Large grain REBa2 Cu3 O7d (RE123) bulk superconductors are also known to trap high magnetic field, which is attractive for various industrial applications. The trapped field can be enhanced by increasing Jc values. It is generally accepted that an addition of RE2 BaCuO5 (RE211) contributes to an improvement of Jc and thus an enhancement of the trapped field. Either an increase in the volume fraction or the refinement of RE211 particles leads to an improvement of pin-
ning through an increase of RE123/RE211 interfacial area [1–3]. Recently, it was reported that melt-textured DyBa2 Cu3 O7d (Dy123) could trap higher magnetic field than Y123, in that a refinement of Dy2 BaCuO5 (Dy211) particles was effective in increasing Jc and trapped field [4]. Hence, Dy123 has significant potential for high field applications. In the present study, we have investigated the size effect of the Dy211 particle on the pinning properties of Dy123 by measuring the dc magnetization and the ac susceptibility. We focus on the suppression of magnetic relaxation and the enhancement of the irreversibility field with reducing Dy211 particle size. 2. Experimental
*
Corresponding author. Tel.: +81-3-3454-9284; fax: +81-33454-9287. E-mail address: [email protected] (K. Inoue).
Dy211 was prepared from commercial Dy2 O3 , BaO2 , and CuO powders. The powders were
0921-4534/02/$ - see front matter Ó 2002 Elsevier Science B.V. All rights reserved. PII: S 0 9 2 1 - 4 5 3 4 ( 0 2 ) 0 1 5 3 7 - X
756
K. Inoue et al. / Physica C 378–381 (2002) 755–758
Table 1 Sample dimension, critical temperature (Tc ) and the average diameter of Dy211 (d) Sample name
Sample dimension (mm)
Tc (K)
d ðlm)
A B C
0:9 1:1 0:5 1:3 1:4 0:5 1:2 1:4 0:5
90.4 89.9 90.7
0.63 0.75 0.85
The c-axis is parallel to the shortest axis.
calcined at different temperatures to control the grain size of Dy211. Dy211 powders in various particle sizes were added to commercial Dy123 powders in 40 mol% and thoroughly mixed. The precursor Dy123/Dy211 powders were pressed into pellets and then melt-processed in air, the details of which are described in Ref. [4]. The average diameter of Dy211 (d) in the melt-textured samples was analyzed with a scanning electron microscope (SEM) [4]. The sample dimension, the critical temperature (Tc ) and the average diameter of Dy211 are listed in Table 1. Dc magnetization measurements were carried out with a Quantum Design MPMS-XL SQUID magnetometer. Ac susceptibility measurements were performed with a Lakeshore 7229 ac susceptometer. In all the magnetic measurements, the magnetic field was applied parallel to the c-axis.
3. Results and discussion Fig. 1 shows the magnetic field dependence of Jc at the reduced temperature T =Tc ¼ 0:83 for three samples. One can see that the Jc is enhanced with the refinement of Dy211 particles in a low field. In the intermediate field region between 1 and 3 T, the shoulder-like secondary peak effect is observed in all the samples, in that Jc is the highest in the sample C with the largest Dy211 particle size due to an enhanced secondary peak effect. It is generally accepted that the secondary peak effect in the Dy123 system is mainly attributed to the field-induced pinning caused by the oxygen deficient clusters, since there is no Dy–Ba solid solution [5]. It is known that the amount of oxygen defects is reduced by the refinement of Dy211 particles, since the Dy211/Dy123 interfaces promote oxygen diffusion. When the magnetic field is increased above 3 T,
Fig. 1. Magnetic field dependence of Jc at the reduced temperature T =Tc ¼ 0:83 for three samples.
the Jc is again higher for the samples with smaller Dy211 particles as shown in the inset of Fig. 1. Fig. 2 shows the magnetic relaxation at 0.25 T and T =Tc ¼ 0:83 for three samples. We started to acquire the data at t ¼ 50 s. One can see the tendency that the magnetic relaxation is slower for the samples with smaller Dy211 particles. This suggests that the Dy123/Dy211 interfacial pinning is effective for the suppression in the flux creep in a relatively low field. We estimated the normalized relaxation rate (S) from the slope of the normalized M–ln t plot in the time window of 1000 < t < 3700 s. Fig. 3 shows the magnetic field dependence of S at T =Tc ¼ 0:83
Fig. 2. Magnetic relaxation at 0.25 T at T =Tc ¼ 0:83 for three samples.
K. Inoue et al. / Physica C 378–381 (2002) 755–758
Fig. 3. Magnetic field dependence of S at T =Tc ¼ 0:83 for three samples.
for three samples. The relaxation rate S is smaller for the sample with the smaller Dy211 particle in a relatively low field, as shown in the inset of Fig. 3. However, the S is the smallest for the sample C with the largest Dy211 particle in an intermediate field. A further increase of the magnetic field again leads to the smaller S for the sample with the smaller Dy211 particles. This suggests that the Dy123/Dy211 interfacial pinning is effective for the suppression in the flux creep up to the high field. In the intermediate field, the decrease in S for the sample with the larger Dy211 particle is ascribed to the field-induced pinning caused by the oxygen deficient clusters. The suppression of the flux creep due to the field-induced pinning is remarkable in this field region, although the interfacial pinning is also active. In a high field region, the suppression of the flux creep due to the interfacial pinning becomes again dominant. Similar suppression effects of relaxation due to the interfacial pinning and the field-induced pinning were also observed in the Nd123 system [6]. Fig. 4 shows the reduced temperature dependence of the irreversibility field (Hirr ). We defined the irreversibility field as the field where Jc ¼ 106 A/m2 . The irreversibility line is enhanced for the sample with the smaller Dy211 particle. This evidences that the Dy123/Dy211 interfacial pinning is active even in the vicinity of the irreversibility line. This result is similar to that of the Nd123 [3] and Y123 system [7].
757
Fig. 4. Temperature dependence of the irreversibility field (Hirr ) determined from the dc magnetization on a reduced temperature scale.
Fig. 5 shows the temperature dependence of the ac susceptibility at the dc field of 8.5 T at 125 Hz for three samples in a reduced temperature scale. The peak of the imaginary part (v00 ) occurs when the ac field penetrates to the center of a sample. The complete Kim model predicts the relation Jc ¼ 0:75hac =a at the peak position of v00 [8], where 2a is the sample thickness and hac is the ac field amplitude. We selected hac to hold the relation Jc ¼ 106 A/m2 and defined the irreversibility temperature (Tirr ) as the peak temperature of v00 .
Fig. 5. Temperature dependence of the ac susceptibility at the dc field of 8.5 T at 125 Hz for three samples on a reduced temperature scale.
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K. Inoue et al. / Physica C 378–381 (2002) 755–758
low and high field region. The suppression in the flux creep occurred with reducing the Dy211 particle size. The field-induced pinning also contributed to the suppression of relaxation in an intermediate filed region. The irreversibility line was enhanced for the sample with the smaller Dy211 particle. This evidences that the Dy123/Dy211 interfacial pinning is active even in the vicinity of the irreversibility field.
Acknowledgements Fig. 6. Temperature dependence of the irreversibility field (Hirr ) determined from the ac susceptibility on a reduced temperature scale.
Fig. 6 shows the reduced temperature dependence of the Hirr determined from the ac susceptibility. The irreversibility line is enhanced with reducing the Dy211 particle. This is consistent with the result of dc magnetization. The electric field is 104 V/m in the case of the ac susceptibility, while it is 108 V/m in the case of the dc magnetization. This suggests that the Dy123/ Dy211 interfacial pinning is effective in the vicinity of the irreversibility line on the wide range of the electric field.
4. Summary We have investigated the size effect of Dy211 particle on the pinning properties of Dy123/Dy211 composites by measuring the dc magnetization and the ac susceptibility. The Jc was enhanced with reducing the Dy211 particle size, particularly in a
This work was supported by the New Energy and Industrial Technology Development Organization (NEDO) as Collaborative Research and Development of Fundamental Technologies for Superconductivity Applications.
References [1] M. Murakami, K. Yamaguchi, H. Fujimoto, N. Nakamura, T. Taguchi, N. Koshizuka, S. Tanaka, Cryogenics 32 (1992) 930. [2] S. Nariki, S.J. Seo, N. Sakai, M. Murakami, Supercond. Sci. Tech. 13 (2000) 778. [3] T. Mochida, N. Chikumoto, M. Murakami, Phys. Rev. B 62 (2000) 1350. [4] S. Nariki, N. Sakai, M. Murakami, Physica C 357–360 (2001) 814. [5] S. Nariki, M. Murakami, Supercond. Sci. Tech. 15 (2002) 786. [6] T. Mochida, N. Chikumoto, M. Murakami, Phys. Rev. B 64 (2001) 064518. [7] D. Yoshimi, M. Migita, E.S. Otabe, T. Matsushita, Physica C 357–360 (2001) 590. [8] T. Ishida, R.B. Goldfarb, S. Okayasu, Y. Kazumata, J. Franz, T. Arndt, W. Schauer, Materials Science Forum, Trans Tech Publications Ltd, Switzerland, 1993, pp. 137– 139.