- Email: [email protected]
Recent developments at the high-field laboratory of Tohoku University
Physica B 246—247 (1998) 360—363
Recent developments at the high-field laboratory of Tohoku University M. Motokawa*, K. Watanabe, S. Miura, S. Awaji, H. Nojiri, I. Mogi, S. Mitsudo, T. Sakon Institute for Materials Research, Tohoku University, Katahira, Sendai 980-77, Japan
Abstract Recent developments and experiments performed at the high-field laboratory of Tohoku University are described. We have (1) hybrid magnets which produce high fields up to 31.1 T, (2) liquid-helium-free superconducting magnets up to 11 T which are available continuously for more than a year, (3) a 20 T superconducting magnet, (4) pulsed field magnets up to 40 T by a 100 kJ bank and (5) repeating pulsed field systems up to 25 T, synchronized with a pulsed neutron source. ( 1998 Elsevier Science B.V. All rights reserved. Keywords: High magnetic field; Hybrid magnet; Pulsed field; Repeating pulsed field
1. Introduction The high-field laboratory of Tohoku University was dedicated in 1981 and succeeded in producing the world’s highest field hybrid magnet with a field of 31.1 T in 1986. Since then, many high-field studies have been done in superconductors, magnetic materials, semiconductors and crystal growth. We first introduce the developments taken place at our facility. The magnets we have are: (1) hybrid magnets which produce up to 31.1 T, (2) helium-free superconducting magnets up to 11 T which are available continuously for more than a year, (3) a 20 T superconducting magnet, (4) pulsed field magnets up to 40 T by a 100 kJ bank and (5)
* Corresponding author. Tel: #81 22 215 2015; Fax: #81 22 215 2016; e-mail: [email protected].
repeating pulsed field systems up to 25 T, synchronized with a pulsed neutron source. They are open for users and many interesting results are reported. In this paper, however, only the studies done by the staff members of the facility are introduced.
2. Steady fields 2.1. The hybrid magnet The polyhelix-type inner magnet being expensive, we are now turning to the poly Bitter type, using hard Cu—Ag alloy. We, recently, succeeded in obtaining on a large scale, 24% silver plates, 0.8 mm thick and 340]340 mm2 square by using a special rolling process and heat treatment. Using these plates, a double Bitter-type magnet with
0921-4526/98/$19.00 ( 1998 Elsevier Science B.V. All rights reserved PII S 0 9 2 1 - 4 5 2 6 ( 9 7 ) 0 0 9 3 5 - 6
M. Motokawa et al. / Physica B 246—247 (1998) 360—363
361
Fig. 1. High-field magnetization hysteresis of the melt textured YBCO bulk at 4.2 K. The inset shows the calculated critical current densities from the data.
52 mm/ warm bore is designed and is currently being built [1]. The hybrid magnet is used for magnetization, magnetotransport and dHvA effect experiments at temperatures down to 10 mK. Some results are presented to ICM97 [2,3] and RHMF [4]. The VSM magnetometer for 30 T was developed for evaluation of high ¹ superconducting bulk # materials [5]. Since the leakage flux is strong (0.4 T at 1 m above the magnet top flange when the central field is 30 T), a usual electric motor does not work. We used ultrasonic motors, which is insensitive to magnetic field, for vibration and position adjustment of sample. Using this equipment, the high-field magnetization measurements of melt textured YBa Cu O bulk were made and the critical 2 3 7 current densities were obtained in fields up to 30 T at 4.2 K as shown in Fig. 1. Recently, we observed water levitation due to diamagnetic effect above 21 T. This is almost
a nongravitational space. Ice, egg and even mouse were confirmed to float. We are planning to grow snow crystal and synthesize some other crystals.
2.2. The liquid-helium-free superconducting magnet By using high-¹ materials (Bi Sr Ca Cu O ) # 2 2 2 3 10 for the current lead conductors of a superconducting magnet, the thermal invasion to the magnet is drastically reduced down to 0.2 W and then a small cryocooler works well enough to cool the magnet down to 4 K. Fields up to 11 T are available by this method continuously for more than a year [6]. This is useful for crystal growth [7], heat treatment of alloys and so on. Using this equipment, the highfield seeding process of YBa Cu O bulk was tried 2 3 7 at 10 T and at about 1000°C for 3 days and an improvement of crystallinity was obtained [8]. A 220 mm/ large bore magnet up to 6 T is also
362
M. Motokawa et al. / Physica B 246—247 (1998) 360—363
Fig. 2. Magnetoresistance of an Nd Sr MnO single crystal at 100 mK. 0.5 0.5 3
installed for investigations of chemical reactions in fields. Magneto-electropolymerization of conducting polypyrrole is being studied and submitted to this symposium [9].
in Fig. 2. The hysteresis width tends to be large with decreasing temperature, which is consistent with the result by Tokura et al. [14].
3. Pulsed fields 2.3. Superconducting magnets 3.1. 40 T pulsed fields Superconducting magnets up to 15 T are available for versatile uses. Experiments of specific heat [10], magnetoresistance [11,12], thermal expansion, magnetization by VSM, AC susceptibility and dHvA effects have been made. In addition, a vector network analyzer for frequencies from 95 to 660 GHz has been installed and cyclotron resonance experiments of Yb (As P ) and 4 0.6 0.4 3 Yb (As P ) were tried [13]. A 20 T super4 0.71 0.29 3 conducting magnet was recently equipped with a dilution refrigerator having a cooling power of 25 mW at 100 mK. This magnet system with 52 mm/ cold bore can provide high homogeneity of 10~6 in 10 mm DSV at 20 T. Magnetoresistance of an Nd Sr MnO single crystal was measured 0.5 0.5 3 at 100 mK and the metal—insulator transition due to the charge order transition with large hysteresis was observed at such a low temperature as shown
Pulsed fields up to 40 T by 100 kJ bank are available at temperatures down to 0.4 K by 3He cryostats, mainly for electron-spin resonance in a frequency range between 90 and 7000 GHz obtained by the use of Gunn Oscillators, backward traveling wave tubes and a FIR laser. Much work for quantum spin systems has been studied [15—18]. Magnetization measurement is a conventional experiment and some examples for quantum spin systems and strongly correlated electron systems are referred to Refs. [19—22].
3.2. Repeating pulsed field For neutron-scattering experiments, a high magnetic field is important to investigate magnetic
M. Motokawa et al. / Physica B 246—247 (1998) 360—363
phase transitions. However, the available fields by superconducting magnets are limited to 12 T. We have been developing pulsed field systems for this purpose. The field is repeated every 2 s and synchronized with a pulsed neutron source [23]. So far the available maximum field has been below 20 T but now it has been improved to 25 T, by using a strong Cu—Ag alloy. None of the neutron facilities in the world provide such high fields. Some experimental results are reported in Refs. [24—27]. References [1] S. Miura, K. Waranabe, M. Motokawa, K. Saskai, Y. Sasaki, Proc. 15th Int. Conf. on Magnet Technology, Beijin, J. Magn. Magn. Mater, 177—181 (1998) 1371. [2] H. Ohta, T. Arioka, E. Kuratov, S. Mitsudo, M. Motokawa, ICM, Cairns, J. Magn. Magn. Mater. 177—181 (1998) 1371. [3] T. Sakon, Y. Nakanishi, M. Ozawa, H. Nojiri, T. Suzuki, M. Motokawa, ICM, Cairns, J. Magn. Magn. Mater. 177—181 (1998) 355. [4] N. Kobayashi, T. Nishizaki, T. Naito, RHMF, Sydney, 1997, submitted. [5] S. Awaji, K. Watanabe, M. Motokawa, Proc. 15th Int. Conf. on Magnet Technology, Beijin, 1997, submitted. [6] K. Watanabe, T. Masumoto, S. Awaji, M. Motokawam, J. Sakuraba, K. Watazawa, T. Hasebe, K. Jikihara, M. Ishihara, Y. Yamada, Sci. Rep. Res. Institutes Tohoku University A 42 (1996) 411. [7] G. Sazaki, E. Yoshida, H. Komatsu, T. Nakada, S. Miyashita, K. Watanabe, J. Crystal Growth 173 (1997) 231. [8] K. Watanabe, S. Awaji, K. Kimura, Jpn. J. Appl. Phys. 36 (1997) 673. [9] I. Mogi, K. Watanabe, M. Motokawa, RHMF, Sydney, 1997, submitted. [10] M. Hiroi, T. Hamamoto, M. Sera. H. Nojiri, N. Kobayashi, M. Motokawa, RHMF, Sydney, 1997, submitted. [11] M. Hiroi, M. Sera, T. Sakon, H. Nojiri, N. Kobayashi, M. Motokawa, S. Kunii, RHMF, Sydney, 1997, submitted.
363
[12] N. Kobayashi, M. Isa, T. Nishizaki, M. Fujiwara, ICM, Cairns, J. Magn. Magn. Mater. 177—181 (1998) 875. [13] R. Pittini, H. Nojiri, M. Motokawa, A. Ochiai, T. Suzuki, RHMF, Sydney, 1997, submitted. [14] Y. Tokura, Physica C 263 (1996) 544. [15] S. Hayashi, S. Kimura, H. Ohta, H. Kikuchi, H. Nagasawa, H. Nojiri, M. Motokawa, ICM, Cairns, J. Magn. Magn. Mater. 177—181 (1998) 667. [16] H. Nojiri, T. Hamamoto, O. Fujita, J. Akimitsu, S. Takagi, M. Motokawa, ICM, Cairns, J. Magn. Magn. Mater. 177—181 (1998) 687. [17] H. Nojiri, T. Hamamoto, O. Fujita, J. Akimitsu, N. Miura, M. Motokawa, RHMF, Sydney, 1997, submitted. [18] T. Fukuda, H. Nojiri, Motokawa, T. Asano, M. Mekata, Y. Ajiro, RHMF, Sydney, 1997, submitted. [19] Y. Matsuoka, Y. Nishimura, S. Mitsudo, H. Nojiri, H. Komatsu, M. Motokawa, K. Kakurai, K. Nakajima, Y. Karasawa, N. Niimura, ICM, Cairns, J. Magn. Magn. Mater. 177—181 (1998) 729. [20] T. Hamamoto, H. Nojiri, M. Motokawa, O. Fujita, A. Ogiwara, J. Akimitsu, presented at ICM, Cairns, 1997. [21] S. Mitsudo, K. Hirano, H. Nojiri, M. Motokawa, K. Hirota, A. Nishizawa, N. Kaneko, Y. Endoh, ICM, Cairns, J. Magn. Magn. Mater. 177—181 (1998) 877. [22] T. Sakon, H. Nojiri, A. Ishiguro, N. Tateiwa, N. Kimiura, A. Sawada, T. Komatsubara, M. Motokawa, RHMF, Sydney, 1997, submitted. [23] H. Nojiri, M. Uchi, S. Watamura, M. Motokawa, H. Kawai, Y. Endoh, T. Shigeoka, J. Phys. Soc. Japan 60 (1991) 2380. [24] K. Takahashi, H. Nojiri, K. Ohoyama, M. Ohashi, Y. Yamaguchi, M. Motokawa, S. Kunii, ICM, Cairns, J. Magn. Magn. Mater. 177—181 (1998) 1097. [25] H. Nojiri, K. Takahashi, T. Fukuda, N. Arai, M. Arai, M. Motokawa, RHMF, Sydney, 1997, submitted. [26] H. Nojiri, K. Takahashi, T. Fukuda, N. Arai, M. Arai, M. Motokawa, Proc. Int. Conf. on Neutron Scattering, Tront, 1997, submitted. [27] K. Takahashi, H. Nojiri, K. Ohoyama, M. Ohashi, Y. Yamaguchi, S. Kunii, M. Motokawa, Proc. Int. Conf. on Neutron Scattering, Tront, 1997, submitted.
Recent developments at the high-field laboratory of Tohoku University M. Motokawa*, K. Watanabe, S. Miura, S. Awaji, H. Nojiri, I. Mogi, S. Mitsudo, T. Sakon Institute for Materials Research, Tohoku University, Katahira, Sendai 980-77, Japan
Abstract Recent developments and experiments performed at the high-field laboratory of Tohoku University are described. We have (1) hybrid magnets which produce high fields up to 31.1 T, (2) liquid-helium-free superconducting magnets up to 11 T which are available continuously for more than a year, (3) a 20 T superconducting magnet, (4) pulsed field magnets up to 40 T by a 100 kJ bank and (5) repeating pulsed field systems up to 25 T, synchronized with a pulsed neutron source. ( 1998 Elsevier Science B.V. All rights reserved. Keywords: High magnetic field; Hybrid magnet; Pulsed field; Repeating pulsed field
1. Introduction The high-field laboratory of Tohoku University was dedicated in 1981 and succeeded in producing the world’s highest field hybrid magnet with a field of 31.1 T in 1986. Since then, many high-field studies have been done in superconductors, magnetic materials, semiconductors and crystal growth. We first introduce the developments taken place at our facility. The magnets we have are: (1) hybrid magnets which produce up to 31.1 T, (2) helium-free superconducting magnets up to 11 T which are available continuously for more than a year, (3) a 20 T superconducting magnet, (4) pulsed field magnets up to 40 T by a 100 kJ bank and (5)
* Corresponding author. Tel: #81 22 215 2015; Fax: #81 22 215 2016; e-mail: [email protected].
repeating pulsed field systems up to 25 T, synchronized with a pulsed neutron source. They are open for users and many interesting results are reported. In this paper, however, only the studies done by the staff members of the facility are introduced.
2. Steady fields 2.1. The hybrid magnet The polyhelix-type inner magnet being expensive, we are now turning to the poly Bitter type, using hard Cu—Ag alloy. We, recently, succeeded in obtaining on a large scale, 24% silver plates, 0.8 mm thick and 340]340 mm2 square by using a special rolling process and heat treatment. Using these plates, a double Bitter-type magnet with
0921-4526/98/$19.00 ( 1998 Elsevier Science B.V. All rights reserved PII S 0 9 2 1 - 4 5 2 6 ( 9 7 ) 0 0 9 3 5 - 6
M. Motokawa et al. / Physica B 246—247 (1998) 360—363
361
Fig. 1. High-field magnetization hysteresis of the melt textured YBCO bulk at 4.2 K. The inset shows the calculated critical current densities from the data.
52 mm/ warm bore is designed and is currently being built [1]. The hybrid magnet is used for magnetization, magnetotransport and dHvA effect experiments at temperatures down to 10 mK. Some results are presented to ICM97 [2,3] and RHMF [4]. The VSM magnetometer for 30 T was developed for evaluation of high ¹ superconducting bulk # materials [5]. Since the leakage flux is strong (0.4 T at 1 m above the magnet top flange when the central field is 30 T), a usual electric motor does not work. We used ultrasonic motors, which is insensitive to magnetic field, for vibration and position adjustment of sample. Using this equipment, the high-field magnetization measurements of melt textured YBa Cu O bulk were made and the critical 2 3 7 current densities were obtained in fields up to 30 T at 4.2 K as shown in Fig. 1. Recently, we observed water levitation due to diamagnetic effect above 21 T. This is almost
a nongravitational space. Ice, egg and even mouse were confirmed to float. We are planning to grow snow crystal and synthesize some other crystals.
2.2. The liquid-helium-free superconducting magnet By using high-¹ materials (Bi Sr Ca Cu O ) # 2 2 2 3 10 for the current lead conductors of a superconducting magnet, the thermal invasion to the magnet is drastically reduced down to 0.2 W and then a small cryocooler works well enough to cool the magnet down to 4 K. Fields up to 11 T are available by this method continuously for more than a year [6]. This is useful for crystal growth [7], heat treatment of alloys and so on. Using this equipment, the highfield seeding process of YBa Cu O bulk was tried 2 3 7 at 10 T and at about 1000°C for 3 days and an improvement of crystallinity was obtained [8]. A 220 mm/ large bore magnet up to 6 T is also
362
M. Motokawa et al. / Physica B 246—247 (1998) 360—363
Fig. 2. Magnetoresistance of an Nd Sr MnO single crystal at 100 mK. 0.5 0.5 3
installed for investigations of chemical reactions in fields. Magneto-electropolymerization of conducting polypyrrole is being studied and submitted to this symposium [9].
in Fig. 2. The hysteresis width tends to be large with decreasing temperature, which is consistent with the result by Tokura et al. [14].
3. Pulsed fields 2.3. Superconducting magnets 3.1. 40 T pulsed fields Superconducting magnets up to 15 T are available for versatile uses. Experiments of specific heat [10], magnetoresistance [11,12], thermal expansion, magnetization by VSM, AC susceptibility and dHvA effects have been made. In addition, a vector network analyzer for frequencies from 95 to 660 GHz has been installed and cyclotron resonance experiments of Yb (As P ) and 4 0.6 0.4 3 Yb (As P ) were tried [13]. A 20 T super4 0.71 0.29 3 conducting magnet was recently equipped with a dilution refrigerator having a cooling power of 25 mW at 100 mK. This magnet system with 52 mm/ cold bore can provide high homogeneity of 10~6 in 10 mm DSV at 20 T. Magnetoresistance of an Nd Sr MnO single crystal was measured 0.5 0.5 3 at 100 mK and the metal—insulator transition due to the charge order transition with large hysteresis was observed at such a low temperature as shown
Pulsed fields up to 40 T by 100 kJ bank are available at temperatures down to 0.4 K by 3He cryostats, mainly for electron-spin resonance in a frequency range between 90 and 7000 GHz obtained by the use of Gunn Oscillators, backward traveling wave tubes and a FIR laser. Much work for quantum spin systems has been studied [15—18]. Magnetization measurement is a conventional experiment and some examples for quantum spin systems and strongly correlated electron systems are referred to Refs. [19—22].
3.2. Repeating pulsed field For neutron-scattering experiments, a high magnetic field is important to investigate magnetic
M. Motokawa et al. / Physica B 246—247 (1998) 360—363
phase transitions. However, the available fields by superconducting magnets are limited to 12 T. We have been developing pulsed field systems for this purpose. The field is repeated every 2 s and synchronized with a pulsed neutron source [23]. So far the available maximum field has been below 20 T but now it has been improved to 25 T, by using a strong Cu—Ag alloy. None of the neutron facilities in the world provide such high fields. Some experimental results are reported in Refs. [24—27]. References [1] S. Miura, K. Waranabe, M. Motokawa, K. Saskai, Y. Sasaki, Proc. 15th Int. Conf. on Magnet Technology, Beijin, J. Magn. Magn. Mater, 177—181 (1998) 1371. [2] H. Ohta, T. Arioka, E. Kuratov, S. Mitsudo, M. Motokawa, ICM, Cairns, J. Magn. Magn. Mater. 177—181 (1998) 1371. [3] T. Sakon, Y. Nakanishi, M. Ozawa, H. Nojiri, T. Suzuki, M. Motokawa, ICM, Cairns, J. Magn. Magn. Mater. 177—181 (1998) 355. [4] N. Kobayashi, T. Nishizaki, T. Naito, RHMF, Sydney, 1997, submitted. [5] S. Awaji, K. Watanabe, M. Motokawa, Proc. 15th Int. Conf. on Magnet Technology, Beijin, 1997, submitted. [6] K. Watanabe, T. Masumoto, S. Awaji, M. Motokawam, J. Sakuraba, K. Watazawa, T. Hasebe, K. Jikihara, M. Ishihara, Y. Yamada, Sci. Rep. Res. Institutes Tohoku University A 42 (1996) 411. [7] G. Sazaki, E. Yoshida, H. Komatsu, T. Nakada, S. Miyashita, K. Watanabe, J. Crystal Growth 173 (1997) 231. [8] K. Watanabe, S. Awaji, K. Kimura, Jpn. J. Appl. Phys. 36 (1997) 673. [9] I. Mogi, K. Watanabe, M. Motokawa, RHMF, Sydney, 1997, submitted. [10] M. Hiroi, T. Hamamoto, M. Sera. H. Nojiri, N. Kobayashi, M. Motokawa, RHMF, Sydney, 1997, submitted. [11] M. Hiroi, M. Sera, T. Sakon, H. Nojiri, N. Kobayashi, M. Motokawa, S. Kunii, RHMF, Sydney, 1997, submitted.
363
[12] N. Kobayashi, M. Isa, T. Nishizaki, M. Fujiwara, ICM, Cairns, J. Magn. Magn. Mater. 177—181 (1998) 875. [13] R. Pittini, H. Nojiri, M. Motokawa, A. Ochiai, T. Suzuki, RHMF, Sydney, 1997, submitted. [14] Y. Tokura, Physica C 263 (1996) 544. [15] S. Hayashi, S. Kimura, H. Ohta, H. Kikuchi, H. Nagasawa, H. Nojiri, M. Motokawa, ICM, Cairns, J. Magn. Magn. Mater. 177—181 (1998) 667. [16] H. Nojiri, T. Hamamoto, O. Fujita, J. Akimitsu, S. Takagi, M. Motokawa, ICM, Cairns, J. Magn. Magn. Mater. 177—181 (1998) 687. [17] H. Nojiri, T. Hamamoto, O. Fujita, J. Akimitsu, N. Miura, M. Motokawa, RHMF, Sydney, 1997, submitted. [18] T. Fukuda, H. Nojiri, Motokawa, T. Asano, M. Mekata, Y. Ajiro, RHMF, Sydney, 1997, submitted. [19] Y. Matsuoka, Y. Nishimura, S. Mitsudo, H. Nojiri, H. Komatsu, M. Motokawa, K. Kakurai, K. Nakajima, Y. Karasawa, N. Niimura, ICM, Cairns, J. Magn. Magn. Mater. 177—181 (1998) 729. [20] T. Hamamoto, H. Nojiri, M. Motokawa, O. Fujita, A. Ogiwara, J. Akimitsu, presented at ICM, Cairns, 1997. [21] S. Mitsudo, K. Hirano, H. Nojiri, M. Motokawa, K. Hirota, A. Nishizawa, N. Kaneko, Y. Endoh, ICM, Cairns, J. Magn. Magn. Mater. 177—181 (1998) 877. [22] T. Sakon, H. Nojiri, A. Ishiguro, N. Tateiwa, N. Kimiura, A. Sawada, T. Komatsubara, M. Motokawa, RHMF, Sydney, 1997, submitted. [23] H. Nojiri, M. Uchi, S. Watamura, M. Motokawa, H. Kawai, Y. Endoh, T. Shigeoka, J. Phys. Soc. Japan 60 (1991) 2380. [24] K. Takahashi, H. Nojiri, K. Ohoyama, M. Ohashi, Y. Yamaguchi, M. Motokawa, S. Kunii, ICM, Cairns, J. Magn. Magn. Mater. 177—181 (1998) 1097. [25] H. Nojiri, K. Takahashi, T. Fukuda, N. Arai, M. Arai, M. Motokawa, RHMF, Sydney, 1997, submitted. [26] H. Nojiri, K. Takahashi, T. Fukuda, N. Arai, M. Arai, M. Motokawa, Proc. Int. Conf. on Neutron Scattering, Tront, 1997, submitted. [27] K. Takahashi, H. Nojiri, K. Ohoyama, M. Ohashi, Y. Yamaguchi, S. Kunii, M. Motokawa, Proc. Int. Conf. on Neutron Scattering, Tront, 1997, submitted.