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Magnetization study of YBaCuO prepared by quench and melt growth process
Physica B 165&166 (1990) 1379-1380 North-Holland
MAGNErIZATION srUOY OF YBaCuO PREPARED BY QJENCH AND MELT GROWI'H PROCESS
S. Gotoh, M. Murakami, N. Koshizuka and S. Tanaka Superconductivity Research Laboratory, International Superconductivity Technology center, 1-10-13, Shinonane, Koto-Ku, Tokyo, 135 Japan
D.C. ll'agnetization measurements were carried out on YBaCuO prepared by the quench arid melt process using a vibrating sample magnetaneter and a SQJID ll'agnetometer below 17K. It was fourrl that the D.C. ll'agnetization behavior of (M; processed YBaCuO at 4.2 K can be quantitatively explained in tenns of Bean mc:del. This sample also can become a strong bulk permanent magnet with a max:imum energy product exceeding 80MGOe at 5 K due to its large pinning force.
growth«(M;)
1. Introduction Bulk sintered high-Tc superconductors have low values of transport critical current density, Jc, because of the defects in the sample, the presence of weak-links at the grain boundaries and their crystal anisotropy of superconductivity • On the other hard., large YBaCuO crystals fabricated by the quench and melt growth ( (M; ) process (1) have exhibited high densities, grain oriented textures and no weaklink, and thereby high Jc values, which exceeded 1x10 4 A/cm2 at 17K and 1T. we report D.C. ll'agnetization properties of the CJvIG processed YBaCuO below 17K and show that they behave as strong bulk permanent magnets. 2. Exper:imental YBa 2Cu 30 x crystals were prepared by the CJvIG process. YBa 2Cu 30 x povrlers were heated to 1400°C for 5 min and quenched by using copper hammers. The quenched plates were again heated to 1100°C and held for 20min, and then cooled to 1000°C at the rate of 100°C/h followed by slow cooling at the rate of 1-5°C/h. The samples were annealed at 600°C for 1h and slowly cooled in flowing oxygen. Rectangular samples, with d:imensions approximately 0.4x3x3mm 3 , were cut from the (M; processed plates so that the surface plane of the plate becanes parallel to the c axis. D.C. ll'agnetization measurements were conducted at 4.2K to 77K using a vibrating sample ll'agnetaneter(VSM) and a SCPID ll'agnetometer with the ll'aximum applied fields of 15kQe and 55kQe respectively. A magnetic field was applied parallel to the c axis and the demagnetizing field was neglected. 3. Results and Discussion 3.1. Magnetization curves The D.C. ll'agnetization curves from 4.2K to
0921-4526/90/$03.50
© 1990 -
77K were measured using a VSM. When the temperature became lower below Tc, magnetic hysteresis rapidly increased and below about 40K the curve was not saturated because of the limited ll'aximum applied field of 15kQe. Since this material shows the linear relationship between the difference of the magnetization between the increasing and decreasing field process and the sample thickness at 17K( 1), Bean critical state mc:del(2) is established in this ll'aterial. Jc value of 14000A/cm2 at 77K and 1T was obtained according to Bean model. The temperature dependence of Jc estimated from the ll'agnetization can be s:imply understood by the flux pinning of fine YZBaCu05(3) inclusions trapped in YBa 2Cupx ll'atnx in this sample. 3.2 Magnetizatlon process based on Bean model In order to investigate the magnetization process at lower temperature using a VSM, we removed the applied field at 4.2K after fieldcooled under a field of 15 kQe. Fig. 1 shows the ll'agnetization curve at 4.2K after fieldcooled. This ll'agnetization is understood based on Bean model. The distribution of the magnetic flux density inside the sample at the points(af) in Fig. 1 is schematically illustrated as shown in Fig.2. At the point (a) in Figs. 1 and 2 no diamagnetic signal is observed because almost all applied flux is trapped in the sample below Tc in the field-cooled process. When the applied field is decreased, the trapped magnetic flux appears as positive magnetization and increases with the flux exclusion in the superficial layers as shown in Figs. l(b,c) and 2(b,c). Then as the applied field is reversed, the applied field enters the sample zigzag like distribution of the magnetic flux as shown in Fig. 2 (e , f , g ) . We also calculated the magnetization based on Bean mc:del assuming the =nstant gradient of
Elsevier Science Publishers B.V. (North-Holland)
s.
1380
Gotoh, M. Murakami, N. Koshizuka, S. Tanaka
20
,......,
,----------------,20
4.2 K
15
_._.._.-..
--.-A-.-~~~.--~
4nM-H
...............
c.:l 10
~ '-"
~ ~
"<:l'
5 0
-5 -10 -15
0
calculated -10
5K 0
-5
5
10
15
H (kOe) FIGURE 1 Magnetization curve at 4.2K after field-cooled under a maqnetic field of 15 kOe.
FIGURE 2
Schematic illustration of magnetic flux distribution in the sample based on magnetization curve in Fig. 1.
flux density inside the sample independently of the applied field as shown in Fig. 1. We used the flux gradient value estimated from the remanent magnetization at the point (a) in Fig. 1, which corresponds tg> the critical =rent densi ty , J c of 1. 48xl 0 AI an2 . The measured values were in good agreement with the calculated values. It was confirmed that Bean lOCldel was well established at 4.2K in the ~ processed sample. We believe that this is attributed to small magnetic field dependence of Jc value within these experimental conditions because of the large upper critical field, H 2. We also obtained similar results in the fieldcooled process of 10 koe with Jc value of 1.6xl0 6 A/an2 • 3 . 3 Superconducting permanent magnets The results shown in Fig. 1 imply that the QMG processed materials can behave as bulk permanent magnets ( 4) because of their large amounts of pinned magnetic flux after the
-20
-15
-10
-5
H (kOe) FIGURE 3
Demagnetization curves at 5K after a magnetic field of 55 kOe.
applied field is removed. Fig. 3 shows the demagnetization curves (B-H and 4nM-H curves) at 5 K after zero field-cooled and a magnetic field of 55 kOe is then applied. The hard magnetic properties derived fran the B-H curve are as follows. 'Ihe residual flux density, Br, is 15.5 kG, the coercive force, bHc, is 18.0 koe and the maximum energy product, (BH)max, is 81.6 !'U)e. On the other hand, the permanent magnetic properties shown in Fig. 1 after field-cooled under a field of 15 kOe are also as follows. Br is 12.1 kG, bHc is 19.3 kOe and (BH)max is 72.5 !'U)e. Using the field-cooling process we can achieve a large maximum energy product with a relatively lower applied field. 4. Conclusion We presented the results of the D.C. magnetization measurements for the ~ processed YBaCuO materials. Magnetization behavior can be qualitatively explained in terms of Bean lOCldel at lower temperature. It is also found that the sample can becane a strong permanent magnet with (BH)max larger than 80MGOe at 5K due to its large pinning force. These results indicate that the material can be used as a bulk permanent magnet. References (1) M. Murakami, M. Morita, K. Doi and K. Miyamoto, Jpn. J. Appl. Phys. 28(1989)1189., Jpn.J. Appl. Phys. 28(1989) L1125. (2) C. P. Bean, Phys. Rev. Lett. 8 (1962) 250. ( 3) M. Murakami, S. Gotch, N. Koshizuka, S. Tanaka, T. Matsushita, S. Karnbe and K. Kitazawa, to appear in a special issue of Cryogenics in 1990. (4) S. L. Wipf and H. L. Laguer, IEEE Trans. Magn., MAG-25, 1877 (1989)
MAGNErIZATION srUOY OF YBaCuO PREPARED BY QJENCH AND MELT GROWI'H PROCESS
S. Gotoh, M. Murakami, N. Koshizuka and S. Tanaka Superconductivity Research Laboratory, International Superconductivity Technology center, 1-10-13, Shinonane, Koto-Ku, Tokyo, 135 Japan
D.C. ll'agnetization measurements were carried out on YBaCuO prepared by the quench arid melt process using a vibrating sample magnetaneter and a SQJID ll'agnetometer below 17K. It was fourrl that the D.C. ll'agnetization behavior of (M; processed YBaCuO at 4.2 K can be quantitatively explained in tenns of Bean mc:del. This sample also can become a strong bulk permanent magnet with a max:imum energy product exceeding 80MGOe at 5 K due to its large pinning force.
growth«(M;)
1. Introduction Bulk sintered high-Tc superconductors have low values of transport critical current density, Jc, because of the defects in the sample, the presence of weak-links at the grain boundaries and their crystal anisotropy of superconductivity • On the other hard., large YBaCuO crystals fabricated by the quench and melt growth ( (M; ) process (1) have exhibited high densities, grain oriented textures and no weaklink, and thereby high Jc values, which exceeded 1x10 4 A/cm2 at 17K and 1T. we report D.C. ll'agnetization properties of the CJvIG processed YBaCuO below 17K and show that they behave as strong bulk permanent magnets. 2. Exper:imental YBa 2Cu 30 x crystals were prepared by the CJvIG process. YBa 2Cu 30 x povrlers were heated to 1400°C for 5 min and quenched by using copper hammers. The quenched plates were again heated to 1100°C and held for 20min, and then cooled to 1000°C at the rate of 100°C/h followed by slow cooling at the rate of 1-5°C/h. The samples were annealed at 600°C for 1h and slowly cooled in flowing oxygen. Rectangular samples, with d:imensions approximately 0.4x3x3mm 3 , were cut from the (M; processed plates so that the surface plane of the plate becanes parallel to the c axis. D.C. ll'agnetization measurements were conducted at 4.2K to 77K using a vibrating sample ll'agnetaneter(VSM) and a SCPID ll'agnetometer with the ll'aximum applied fields of 15kQe and 55kQe respectively. A magnetic field was applied parallel to the c axis and the demagnetizing field was neglected. 3. Results and Discussion 3.1. Magnetization curves The D.C. ll'agnetization curves from 4.2K to
0921-4526/90/$03.50
© 1990 -
77K were measured using a VSM. When the temperature became lower below Tc, magnetic hysteresis rapidly increased and below about 40K the curve was not saturated because of the limited ll'aximum applied field of 15kQe. Since this material shows the linear relationship between the difference of the magnetization between the increasing and decreasing field process and the sample thickness at 17K( 1), Bean critical state mc:del(2) is established in this ll'aterial. Jc value of 14000A/cm2 at 77K and 1T was obtained according to Bean model. The temperature dependence of Jc estimated from the ll'agnetization can be s:imply understood by the flux pinning of fine YZBaCu05(3) inclusions trapped in YBa 2Cupx ll'atnx in this sample. 3.2 Magnetizatlon process based on Bean model In order to investigate the magnetization process at lower temperature using a VSM, we removed the applied field at 4.2K after fieldcooled under a field of 15 kQe. Fig. 1 shows the ll'agnetization curve at 4.2K after fieldcooled. This ll'agnetization is understood based on Bean model. The distribution of the magnetic flux density inside the sample at the points(af) in Fig. 1 is schematically illustrated as shown in Fig.2. At the point (a) in Figs. 1 and 2 no diamagnetic signal is observed because almost all applied flux is trapped in the sample below Tc in the field-cooled process. When the applied field is decreased, the trapped magnetic flux appears as positive magnetization and increases with the flux exclusion in the superficial layers as shown in Figs. l(b,c) and 2(b,c). Then as the applied field is reversed, the applied field enters the sample zigzag like distribution of the magnetic flux as shown in Fig. 2 (e , f , g ) . We also calculated the magnetization based on Bean mc:del assuming the =nstant gradient of
Elsevier Science Publishers B.V. (North-Holland)
s.
1380
Gotoh, M. Murakami, N. Koshizuka, S. Tanaka
20
,......,
,----------------,20
4.2 K
15
_._.._.-..
--.-A-.-~~~.--~
4nM-H
...............
c.:l 10
~ '-"
~ ~
"<:l'
5 0
-5 -10 -15
0
calculated -10
5K 0
-5
5
10
15
H (kOe) FIGURE 1 Magnetization curve at 4.2K after field-cooled under a maqnetic field of 15 kOe.
FIGURE 2
Schematic illustration of magnetic flux distribution in the sample based on magnetization curve in Fig. 1.
flux density inside the sample independently of the applied field as shown in Fig. 1. We used the flux gradient value estimated from the remanent magnetization at the point (a) in Fig. 1, which corresponds tg> the critical =rent densi ty , J c of 1. 48xl 0 AI an2 . The measured values were in good agreement with the calculated values. It was confirmed that Bean lOCldel was well established at 4.2K in the ~ processed sample. We believe that this is attributed to small magnetic field dependence of Jc value within these experimental conditions because of the large upper critical field, H 2. We also obtained similar results in the fieldcooled process of 10 koe with Jc value of 1.6xl0 6 A/an2 • 3 . 3 Superconducting permanent magnets The results shown in Fig. 1 imply that the QMG processed materials can behave as bulk permanent magnets ( 4) because of their large amounts of pinned magnetic flux after the
-20
-15
-10
-5
H (kOe) FIGURE 3
Demagnetization curves at 5K after a magnetic field of 55 kOe.
applied field is removed. Fig. 3 shows the demagnetization curves (B-H and 4nM-H curves) at 5 K after zero field-cooled and a magnetic field of 55 kOe is then applied. The hard magnetic properties derived fran the B-H curve are as follows. 'Ihe residual flux density, Br, is 15.5 kG, the coercive force, bHc, is 18.0 koe and the maximum energy product, (BH)max, is 81.6 !'U)e. On the other hand, the permanent magnetic properties shown in Fig. 1 after field-cooled under a field of 15 kOe are also as follows. Br is 12.1 kG, bHc is 19.3 kOe and (BH)max is 72.5 !'U)e. Using the field-cooling process we can achieve a large maximum energy product with a relatively lower applied field. 4. Conclusion We presented the results of the D.C. magnetization measurements for the ~ processed YBaCuO materials. Magnetization behavior can be qualitatively explained in terms of Bean lOCldel at lower temperature. It is also found that the sample can becane a strong permanent magnet with (BH)max larger than 80MGOe at 5K due to its large pinning force. These results indicate that the material can be used as a bulk permanent magnet. References (1) M. Murakami, M. Morita, K. Doi and K. Miyamoto, Jpn. J. Appl. Phys. 28(1989)1189., Jpn.J. Appl. Phys. 28(1989) L1125. (2) C. P. Bean, Phys. Rev. Lett. 8 (1962) 250. ( 3) M. Murakami, S. Gotch, N. Koshizuka, S. Tanaka, T. Matsushita, S. Karnbe and K. Kitazawa, to appear in a special issue of Cryogenics in 1990. (4) S. L. Wipf and H. L. Laguer, IEEE Trans. Magn., MAG-25, 1877 (1989)