Physica C 463–465 (2007) 398–401
www.elsevier.com/locate/physc

Trapped ﬁeld and temperature rise in rectangular-shaped HTSC
bulk magnetized by pulse ﬁelds
T. Tateiwa a, Y. Sazuka a, H. Fujishiro a,*, H. Hayashi b, T. Nagafuchi b, T. Oka ca

Faculty of Engineering, Iwate University, 4-3-5 Ueda, Morioka 020-8551, Japanb
Kyushu Electric Power Co. Inc., 2-1-47 Shiobaru, Fukuoka 815-8520, Japanc
Faculty of Engineering, Niigata University, Niigata, Niigata 950-2181, Japan

Received 31 October 2006; received in revised form 28 December 2006; accepted 6 March 2007
Available online 18 May 2007

Abstract
A rectangular-shaped GdBaCuO bulk (33 · 33 · 20 mm3) has been magnetized by pulse ﬁelds with various strengths from Bex = 3 T
to 7 T at 44 K and 20 K. The time dependences of the local ﬁelds and temperatures have been measured at ﬁve positions on the bulk
surface. The ﬂux movement, ﬂux trapping and the heat generation are closely related for lower applied ﬁelds, i.e., the temperature riseis larger at the speciﬁed positions, where a large number of magnetic ﬂuxes are trapped. The heat generation is mainly due to the pinningloss in this condition. The maximum trapped ﬁeld BT = 4.0 T can be realized on the bulk surface by a modiﬁed multi-pulse techniquewith stepwise cooling (MMPSC) method, on which BT reaches only 2.5 T at 20 K for a single pulse application.
 2007 Elsevier B.V. All rights reserved.
PACS: 74.25.Bt; 74.80.Bj; 74.60.Ge
Keywords: Pulse ﬁeld magnetization; Rectangular-shaped bulk; Temperature rise; Trapped ﬁeld; MMPSC method

1. Introduction
REBaCuO superconducting bulks (RE: rare earth element) are used as a conductor with zero resistance forpower current leads, as a levitation device using a pinningeﬀect and as a high strength bulk magnet using a strong
pinning force [1]. A ﬁeld-cooled magnetization (FCM)
using a superconducting magnet (SM) is a usual techniqueto magnetize the bulks and makes the trapped ﬁeld maximize. A pulse ﬁeld magnetization (PFM) technique has
been intensively studied because of the inexpensive andmobile experimental setup with no use of SM. Several
approaches have been performed and succeeded to enhance
the trapped ﬁeld by an iteratively magnetizing pulsed-ﬁeld
method with reducing amplitude (IMRA) [2], a multi-pulse
technique with stepwise cooling (MPSC) [3] and so on.
*

Corresponding author. Tel./fax: +81 19 621 6363.
E-mail address: fujishiro@iwate-u.ac.jp (H. Fujishiro).

0921-4534/$ - see front matter  2007 Elsevier B.V. All rights reserved.
doi:10.1016/j.physc.2007.03.442

Disk-shaped REBaCuO bulks are commonly used for abasic study and practical applications [4]. Rectangularshaped bulks have been also fabricated and used for thespeciﬁed applications such as a ﬂywheel [5], magnetic bearings [6] and a magnetic separation system [7]. We havedeveloped the bulk magnet system with ﬁve-aligned rectangular-shaped REBaCuO bulks, which has been used for themagnetic separation to purify waste water [8]. When therectangular-shaped bulk is magnetized by PFM using asolenoid-type pulse coil, diﬀerent behaviors as for the magnetic ﬂux intrusion and the ﬁeld trapping proﬁle are supposed, compared with those for a disk-shaped bulk.
Because the length of the ﬂux intrusion path from theperiphery to the bulk center is not identical at each position. However, there are no systematic reports of thetrapped ﬁeld properties for the rectangular-shaped bulks
by PFM.
In this paper, we investigate the time dependences ofboth the local ﬁelds BL(t) and temperatures T(t) at identical

T. Tateiwa et al. / Physica C 463–465 (2007) 398–401

positions on the surface of the cryocooled rectangularshaped GdBaCuO bulk after applying pulse ﬁelds. Therelation between the ﬂux intrusion and the temperature riseis discussed. A two-stage PFM technique, named as a modiﬁed multi-pulse technique with stepwise cooling(MMPSC) method [9], is applied in order to enhance thetrapped ﬁeld, in which the highest record of 5.20 T had
been realized on the disk-shaped GdBaCuO bulk [10].
2. Experimental
The rectangular-shaped GdBaCuO bulk (Nippon SteelCorporation) was used with 33 · 33 mm2 in the ab-planeand 18 mm in thickness along the c-axis, which was cut
from a disk-shaped bulk 45 mm in diameter. The bulk
was mounted on soft iron yoke cylinder 40 mm in diameterand 20 mm in thickness and tightly anchored onto the cold
stage of a Giﬀord–McMahon (GM) cycle refrigerator. Thebulk was evacuated using an oil diﬀusion pump and themagnetizing solenoid coil was placed outside the vacuum
chamber. The time dependences of the local magnetic ﬁelds
BL(t) and temperatures T(t) were measured at ﬁve positions
on the bulk surface during PFM as shown in Fig. 1. Twosets of the measuring conﬁgurations were performed tomeasure the BL(t) and T(t). The doted lines showed thegrowth sector boundaries (GSBs) and a point of intersection of GSRs slightly shifted from the bulk center. InFig. 1a, four Hall sensors (F W Bell, BHT 921) and a thermocouple (type T, 76 lm in diameter) were symmetricallyadhered at P1–P4 and at the bulk center (P0), respectively.
Hereafter, we abbreviate this conﬁguration as set A. The
each distance between P0 and P1–P4 was 9 mm. In theset B, a Hall sensor and four thermocouples were set at
P0 and P1–P4, respectively, as shown in Fig. 1b. The initial
temperature Ts of the bulk surface was ﬁxed at 44 K and
20 K and a single pulse ﬁeld Bex from 3 T to 7 T with a risetime of 12 ms was applied to the bulk. In order toenhance the BT value, the MMPSC method was applied.
In the method, a pulse ﬁeld Bex(1) = 4.94 T was applied
twice (No. 1 and No. 2 pulses) at Ts(1) = 44 K at the ﬁrst
stage in order to trap a small number of magnetic ﬂuxes
in the bulk. At the second stage, the bulk was cooled down
to Ts(2) = 20 K and a higher pulse ﬁeld Bex(2) = 6.87 T wasapplied twice (No. 3 and No. 4), after recovering to Ts(2).

Fig. 1. Two sets of the measuring conﬁgurations of the local magneticﬁelds BL(t) and temperatures T(t) on the bulk surface (set A and set B).

399

3. Results and discussion
Fig. 2a shows the trapped ﬁeld BT at P0 in the set B conﬁguration as a function of the applied ﬁeld Bex. BT at
Ts = 44 K sharply increases for Bex higher than 3 T, takesa maximum and then decreases with increasing Bex. TheBT Bex curve at Ts = 20 K is a similar behavior with aslight shift to the higher Bex. The maximum BT was 2.1 Tfor Bex = 5.49 T at Ts = 44 K and 2.4 T for Bex = 6.20 T
at Ts = 20 K. These results come from the increase in thepinning force Fp with decreasing Ts. Fig. 2b shows the maximum temperature rise DTmax at P0 in the set A conﬁguration as a function of Bex. DTmax increases with increasing
Bex and the DTmax values at Ts = 20 K are larger than thoseat Ts = 44 K.
Fig. 3a and b shows the time evolutions of the local
ﬁelds BL(t) and the temperatures T(t) at P1–P4 after applying pulse ﬁeld of Bex = 3.97 T at 44 K. The strength ofBex = 3.97 T is relatively low because only a small numberof the magnetic ﬂuxes intrude into the bulk center as shownin Fig. 2a. In Fig. 3a, BL(t) at P4 rises up with a sharp peakwhich is nearly equal to the Bex value. The peak height ofBL(t) at P1–P3 is at most 1–1.5 T. These results suggest thatthe magnetic ﬂux starts to intrude from P4 more preferentially. The trapped ﬁeld BT (=BL(t = 200 ms)) at P4 is as
small as 1 T which is larger than that at P1–P3. In
Fig. 3b, T(t) at P4 also shows a sharp peak at aroundt  2 s and then decreases.
Fig. 4a and b shows the time evolutions of BL(t) and T(t)at P1–P4 after applying pulse ﬁeld of Bex = 4.80 T at 44 K.
Contrary to the results in Fig. 3a, BL(t) at P1, P2 and P4
shows a sharp peak, which suggests that the magneticﬂuxes preferentially intrude into the bulk from these positions for higher Bex application. On the other hand, BL(t)at P3 rises up to at most 2.5 T. The BT value at P2 andP3, which is 1.5–1.8 T at t = 200 ms, is larger than that at
P1 and P4 (BT = 1 T). In Fig. 4b, the temperature rise at
P2 and P3 is 2–5 K larger than that at P1 and P4 andFig. 2. (a) The trapped ﬁeld BT (set B) and (b) the maximum temperaturerise DTmax (set A) at the bulk center (P0) as a function of the applied pulse
ﬁeld Bex at Ts = 20 K and 44 K.

400

T. Tateiwa et al. / Physica C 463–465 (2007) 398–401

Fig. 3. The time evolutions of (a) the local ﬁelds BL(t) and (b) thetemperatures T(t) at P1–P4 after applying pulse ﬁeld of Bex = 3.97 T at
Ts = 44 K.

Fig. 4. The time evolutions of (a) the local ﬁelds BL(t) and (b) thetemperatures T(t) at P1–P4 after applying pulse ﬁeld of Bex = 4.80 T at
44 K.

T(t) at P2 shows a clear peak. These results shown in Figs.
3 and 4 indicate that the ﬂux intrusion and the ﬂux trap areclosely related with the heat generation.
Fig. 5a shows the position dependence of BT (set A) at
Ts = 44 K for various applied ﬁelds Bex. The position, at
which the ﬂuxes are trapped preferentially, changes
depending on the strength of Bex. At the positions P3and P4, BT increases with increasing Bex up to 5.49 T,
but BT at P1 and P2 decreases for the application ofBex = 5.49 T which comes from the escape of ﬂuxes dueto the large temperature rise. Fig. 5b shows the position
dependence of the maximum temperature rise DTmax(set B) at Ts = 44 K for various applied ﬁelds Bex. It should
be noted that the position dependence of DTmax resembles
that of BT. Heat generation Q is the sum of the pinning loss
Qp due to the ﬂux trap and the viscous loss Qv due to theﬂux movement [11]. The similarity of the position dependences of BT and DTmax suggests that the heat generation
is mainly due to Qp. The similar behaviors also occur atFig. 5. The position dependence of (a) the trapped ﬁeld BT (set A) and (b)the maximum temperature rise DTmax (set B) at Ts = 44 K for various
applied ﬁelds Bex.

Ts = 20 K for Bex < 5 T. For higher Bex (>5.5 T at
Ts = 44 K, >6.1 T at Ts = 20 K), Qv is dominant due tothe large temperature rise and decrease in the pinning force
Fp [12]. In this way, the measurements of the local ﬁeldBL(t) and the temperature T(t) at identical positions giveus the valuable information as for the dynamical motion
and the trapping of the magnetic ﬂuxes.
In order to enhance the BT value, the MMPSC technique was applied. Fig. 6a and b shows the time dependences of the applied ﬁeld l0Ha(t) and the local ﬁelds
BL(t) after applying pulse No. 1 (Ts(1) = 44 K, Bex(1) =4.78 T) and No. 3 (Ts(2) = 20 K, Bex(2) = 6.72 T) in theMMPSC method, respectively. BL(t) was measured at thepositions P0, P3 and P5 as shown in the inset of Fig. 6b.
For No. 1 pulse at the ﬁrst stage, BT = 2 T was trapped,and for No. 3 pulse at the second stage, BT = 4.0 T and
2.9 T were trapped at P3 and P0, respectively. The BT
values are higher than those by a single pulse application

Fig. 6. The time dependences of the applied ﬁeld l0Ha(t) and the local
ﬁelds BL(t) at P0, P3 and P5 after applying pulse ﬁelds of the (a) pulse No.
1 at the ﬁrst stage and (b) pulse No. 3 at the second stage in the MMPSC
method.

T. Tateiwa et al. / Physica C 463–465 (2007) 398–401

shown in Fig. 2a. These results suggest that the rectangular-shaped bulk used in this study has a potential to trap
high BT value and that the MMPSC method is an eﬀective
technique to enhance the BT value.
In summary, a rectangular-shaped large GdBaCuO bulk
has been magnetized by pulse ﬁelds with various strengths
at Ts = 44 K and 20 K and the local ﬁelds BL(t) and temperatures T(t) have been measured at identical ﬁve positions on the bulk surface. The temperature rise is larger
at the speciﬁed positions, where a large number of magnetic ﬂuxes are trapped. The heat generation is mainly
due to the pinning loss Qp. The maximum trapped ﬁeld
BT can reach only 2.5 T at 20 K for a single pulse application, but the BT value is enhanced up to 4.0 T by a
MMPSC method.
References[1] M. Murakami, N. Sakai, T. Higuchi, S.I. Yoo, Supercond. Sci.
Technol. 9 (1996) 1015.

401[2] U. Mizutani, T. Oka, Y. Itoh, Y. Yanagi, M. Yoshikawa, H. Ikuta,Appl. Supercond. 6 (1998) 235.
[3] M. Sander, U. Sutter, R. Koch, M. Klaser, Supercond. Sci. Technol.
13 (2000) 841.
[4] S. Nariki, M. Murakami, Supercond. Sci. Technol. 15 (2002) 786.
[5] N. Koshizuka, Physica C 445–448 (2006) 1103.
[6] K. Demachi, I. Masaie, T. Ichihara, M. Kita, Physica C 426–431(2005) 826.
[7] H. Hayashi, K. Tsutsumi, N. Saho, N. Nishijima, K. Asano, Physica
C 392–396 (2003) 745.
[8] A. Fujiwara, T. Tateiwa, H. Fujishiro, H. Hayashi, T. Nagafuchi,T. Oka, Physica C 445–448 (2006) 399.
[9] H. Fujishiro, M. Kaneyama, T. Tateiwa, T. Oka, Jpn. J. Appl. Phys.
44 (2005) L1221.
[10] H. Fujishiro, T. Tateiwa, A. Fujiwara, T. Oka, H. Hayashi, Physica C
445–448 (2006) 334.
[11] H. Fujishiro, K. Yokoyama, M. Kaneyama, T. Oka, K. Noto,Physica C 412–414 (2004) 646.
[12] H. Fujishiro, M. Kaneyama, K. Yokoyama, T. Oka, K. Noto,
Supercond. Sci. Technol. 18 (2005) 158.