Physica C 469 (2009) 1250–1253

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Physica C
journal homepage: www.elsevier.com/locate/physc

Enhancement of total trapped ﬂuxes on u65 mm GdBaCuO bulk
by multi-pulse techniques
H. Fujishiro a,*, K. Kakehata a, T. Naito a, Y. Yanagi b, Y. Itoh bab

Faculty of Engineering, Iwate University, 4-3-5 Ueda, Morioka 020-8551, JapanIMRA Material R&D Co. Ltd., 2-1 Asahi-cho, Kariya 448-0032, Japana r t i c l e

i n f oArticle history:
Available online 30 May 2009
PACS:
74.25.Bt
74.80.Bj
74.60.Ge
Keywords:
Bulk superconductor
Pulsed ﬁeld magnetization
SPA+IMRA method
Total trapped ﬂux density

a b s t r a c t
We have investigated the total trapped ﬂux UT(z) on the u65 mm GdBaCuO superconducting bulk as afunction of distance z from the bulk surface magnetized by a successive pulse ﬁeld application (SPA) withidentical magnitude and subsequent iterative pulsed-ﬁeld magnetization method with reducing theamplitude (IMRA) at various temperatures Ts. The UT(z) value was enhanced by the IMRA process andreached 5.02 mWb on the bulk surface at Ts = 40 K, which was about 1.7 times larger than that at theend of SPA. The UT (4 mm) value at 40 K by the SPA+IMRA method was as high as UFC
T (4 mm) by ﬁeld
cooled magnetization under Bex = 3 T at 48 K. The IMRA method is quite effective to enhance the UT value
for large superconducting bulks.
Ó 2009 Elsevier B.V. All rights reserved.

1. Introduction
To magnetize the REBaCuO superconducting bulks (RE: rareearth element) as a strong quasi-permanent magnet for practicalapplications such as a magnetic separation for environmental
cleaning [1] and a drug delivery system (DDS) for medical applications [2], a pulsed-ﬁeld magnetization (PFM) is suitable, instead ofa conventional ﬁeld cooled magnetization (FCM), because PFM is
an inexpensive and mobile experimental setup. The trapped ﬁeld
BPT by PFM was, however, pretty smaller than the trapped ﬁeld
BFC
T attained by FCM below 77 K because of the large temperaturerise caused by the dynamical motion of magnetic ﬂuxes in the bulk.
Several approaches have been performed and succeeded toenhance BPT around 77 K such as an iteratively magnetizing
pulsed-ﬁeld method with reducing amplitude (IMRA) [3] and amulti-pulse technique with stepwise cooling (MPSC) [4]. We havesystematically studied the time and spatial dependences of thetemperature T(t, x), the local ﬁeld BL(t) and the trapped ﬁeld BPT
on the surface of cryo-cooled REBaCuO bulks [5]. To enhance BPT ,we proposed a new PFM technique called a modiﬁed MPSC(MMPSC), which consisted of the two-stage temperature procedures [6]. Using the MMPSC method, we have succeeded in estab-* Corresponding author. Tel./fax: +81 19 621 6363.
E-mail address: fujishiro@iwate-u.ac.jp (H. Fujishiro).
0921-4534/$ - see front matter Ó 2009 Elsevier B.V. All rights reserved.
doi:10.1016/j.physc.2009.05.113

lishing a record of high-ﬁeld trapping of BPT ¼ 5:20 T on the u45 mm
GdBaCuO bulk at 29 K to date [7], on which the maximum BPT of 3.6
T was attained by a single pulse application.
Recently, REBaCuO superconducting bulks with diameter larger
than 60 mm are on the commercial market and even a single-grainbulk of 140 mm in diameter can be realized [8]. According to
Bean’s critical state model, a trapped ﬁeld BT at the bulk centeris proportional to the diameter of the bulk disk d, and a total
trapped ﬂux density UT is proportional to the cubic of d, if the critical current density Jc of the bulk material is identical. Anotheradvantage of the large bulk magnet is that the magnetic ﬁeld
can reach a long distance, which is especially useful for the practical applications such as electric motor, generator and sputtering
cathode.
We have investigated the trapped ﬁeld characteristics on the
u65 mm GdBaCuO bulk by the successive pulse application (SPA)[9] and the MMPSC method [10]. The maximum trapped ﬁeld on
the u65 mm bulk using SPA was as low as BPT ¼ 1:9 T at 40 K, but
BPT was enhanced to 3.0 T using the MMPSC method, which werefairly smaller than those on the u45 mm GdBaCuO bulk [7]. However, the UT value for the large bulk is expected to enhance by the
IMRA method because the UT value of the u45 mm GdBaCuO bulk
had been about 30% enhanced by the IMRA method after the termination of the MMPSC method [11].
In this paper, we perform the SPA+IMRA method on the
u65 mm GdBaCuO bulk under several temperatures Ts and appliedH. Fujishiro et al. / Physica C 469 (2009) 1250–1253

pulse ﬁelds Bex and investigate the effect of the enhancement of theUT value on the multi pulse technique. We compare the UT value
by the SPA+IMRA method with the UFC
T value obtained by the FCM.
2. Experimental procedure
A u65 mm GdBaCuO superconducting bulk disk of 20 mm inthickness (Nippon Steel) was used in this study. The trapped ﬁeld
BFC
T by FCM was as high as 1.92 T at 77 K. The bulk was mounted
on a soft iron yoke cylinder and tightly anchored onto the cold
stage of a Gifford-McMahon (GM) cycle helium refrigerator. The
experimental setup around the bulk was described elsewhere[10]. The magnetizing solenoid coil, which generated the pulse
ﬁeld up to Bex = 6.7 T with a rise time of 12 ms and a duration of
100 ms, was placed outside the vacuum chamber, in which thecentral axis of the resulting ﬁeld coincides with that of the bulk.
The temperature Ts of the bulk was controlled over the range from60 K to 40 K. Fig. 1 shows the experimental sequence of the
SPA+IMRA process. Three magnetic pulses (Nos. 1–3) with nearly
the same amplitude Bex(SPA) (=B1=B2=B3) were applied sequentially after re-cooling to Ts. From the No. 4 pulse, the IMRA process
started, in which applied pulsed ﬁelds Bex(IMRA) = Bn (>Bn+1) were

Fig. 1. The experimental sequence of the SPA+IMRA method.

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iteratively reduced down to 3.5 T by a 0.3 T step at constant Ts.
Two-dimensional trapped ﬁeld proﬁle BT = BT(z) was mapped at
the distance z (=0.5, 4 and 8 mm) above the bulk surface, stepwise
with a pitch of 1 mm by scanning an axial-type Hall sensor (F.W.
Bell, BHA 921) inside the vacuum chamber using an x–y stage controller. The total amount of the total trapped magnetic ﬂux density
UT = UT(z) was calculated by integrating the BT(z) value over theregion where it was positive. The BFC
T (z) proﬁles by FCM were alsomeasured at temperatures from 38 K to 77 K using a cryo-cooled
superconducting magnet and UFC
T (z) was estimated. During FCM,
the static magnetic ﬁeld of 3 T was decreased down to 0 T in
18 min.
3. Results and discussion
Fig. 2a and b, respectively, show the examples of the trapped
ﬁeld proﬁle BT (0.5 mm) for the ﬁrst (No. 1) and the last (No. 13)
pulse application in the SPA+IMRA method (Ts = 40 K, B1 = 6.6 T).
For the No. 1 pulse, a concave BT proﬁle with nearly the axial symmetry can be observed and, for the No. 13 pulse, the BT value entirely increased remaining the concave proﬁle. Hereafter, weshow the cross section of the BT proﬁle along the y-axis insteadof the two-dimensional BT proﬁle, for simplicity.
Fig. 3a shows the pulse number dependence of the cross sectionof the trapped ﬁeld proﬁle BT (0.5 mm) for the SPA+IMRA method(Ts = 40 K, B1 = 6.6 T). For the No. 1 pulse, the concave BT proﬁlecan be seen, which was identical with the cross section of Fig. 2a.
The BT (0.5 mm) value at the bulk periphery gradually increased
with increasing pulse number. On the other hand, the BT(0.5 mm) value at the bulk center only slightly increases. For theNo. 13 pulse application (B13 = 3.5 T) in the IMRA process, the BT
increment at the bulk periphery seems to saturate. Fig. 3b shows
the trapped ﬁeld proﬁle BT(z) after applying the No. 13 pulse as afunction of the distance z from the bulk surface. The BT(z) value
at the bulk periphery drastically decreases with increasing z, butthat at the bulk center remains constant. As a result, the trapped
ﬁeld proﬁle changes from concave (z = 0.5 mm) to trapezoid(z = 8 mm).
Fig. 4a shows the pulse number dependence of the BT (0.5 mm)
proﬁles for the SPA+IMRA method (Ts = 40 K, B1 = 5.4 T). Since theapplied pulse ﬁeld B1 is smaller than that in Fig. 3a, only a small

Fig. 2. The trapped ﬁeld proﬁles BT (0.5 mm) at Ts = 40 K after applying the (a) No. 1 pulse (B1 = 6.6 T) in SPA and (b) No. 13 pulse (B13 = 3.5 T) in IMRA.

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H. Fujishiro et al. / Physica C 469 (2009) 1250–1253

Fig. 3. (a) The BT (0.5 mm) proﬁle vs. the pulse number n and (b) BT(z) for the No. 13
pulse vs. the distance z from the bulk surface for the SPA+IMRA method (Ts = 40 K,
B1 = 6.6 T).

amount of the magnetic ﬂuxes can intrude and can be trapped at
the bulk center. In the IMRA process, the BT (0.5 mm) value atthe bulk periphery gradually increased and saturated with increasing pulse number. Fig. 4b shows the BT (0.5 mm) proﬁles for the
SPA+IMRA method (Ts = 60 K, B1 = 6.6 T) at higher Ts. For the No.
1 pulse application, the BT (0.5 mm) proﬁle shows nearly thecone-shaped one which results from the weaker pinning force thanthat at 40 K. The magnetic ﬂuxes were additionally trapped both at
the bulk periphery and bulk center in the IMRA process.
Fig. 5 shows the total trapped ﬂuxes UT (0.5 mm) vs. the applied
pulse ﬁeld Bex for each step in the SPA+IMRA method. In the ﬁgure,the numerals represent the pulse number n for each SPA+IMRA
method. The UT (0.5 mm) value gradually increases with increasing pulse number and then saturates for Bex < 4 T. The ﬁnal UT(0.5 mm) value depends on both Ts and B1 values in the SPA process and increases with lowering Ts. It was found that the optimum
B1 value should exist to maximize the ﬁnal UT (0.5 mm) value ateach Ts. In this study, we attained the maximum UT (0.5 mm) valueof 5.05 mWb for the u65 mm GdBaCuO bulk using the SPA+IMRA
method at Ts = 40 K and at B1 = 6.6 T. During the IMRA process,the BT (0.5 mm) value slightly increased from 1.17 T (No. 4 pulse)
to 1.39 T (No. 13 pulse).
Fig. 6 shows the total trapped ﬂuxes UT(z) obtained in thisstudy, as a function of the distance z from the bulk surface for
the SPA+IMRA process at Ts = 40 K (B1 = 6.6 T) and Ts = 60 K

Fig. 4. The pulse number dependence of the BT (0.5 mm) proﬁles for the SPA+IMRA
method ((a) Ts = 40 K, B1 = 5.4 T and (b) Ts = 60 K, B1 = 6.6 T).

Fig. 5. The total trapped ﬂuxes UT (0.5 mm) vs. the applied pulse ﬁeld Bex for eachcondition in the SPA+IMRA method. In the ﬁgure, the numerals represent the pulse
number n.

(B1 = 6.6 T). UT(z) gradually decreased with increasing z; UT(0.5 mm) = 5.05 mWb and UT (8 mm) = 3.19 mWb at Ts = 40 K
and at B1 = 6.6 T. In the ﬁgure, the UFC
T (z) values by FCM underH. Fujishiro et al. / Physica C 469 (2009) 1250–1253

1253

of distance z from the bulk surface using a successive pulse ﬁeld
application (SPA) with identical magnitude and subsequent iterative pulsed-ﬁeld magnetization method with reducing the amplitude (IMRA) at Ts = 40 and 60 K. The UT (0.5 mm) value wasenhanced by the IMRA method and reached 5.02 mWb on the bulk
surface at Ts = 40 K, which was about 1.7 times larger than that at
the end of SPA. The UT (4 mm) value by SPA+IMRA process was ashigh as the UFC
T (4 mm) value by ﬁeld cooled magnetization under
3 T at 48 K. The IMRA method is effective for the enhancement of
the UT value for large superconducting bulks. The UT value closely
depends on the shape of the trapped ﬁeld proﬁle at the end of the
SPA process, the magnitude of the applied ﬁeld Bex during both SPA
and IMRA processes, diameter of the bulk, the temperature Ts andso on. In this study, the maximum Bex was 6.6 T for the experimental setup reason and we cannot realize the convex shape at 40 K.
Within our experimental conditions (Ts P 40 K, Bex 6 6.6 T), themaximum UT value was realized under the concave trapped ﬁeld
proﬁle. A detailed study is in progress.
Fig. 6. The UT(z) values as a function of the distance z from the bulk surface by the
SPA+IMRA method at Ts = 40 K and 60 K (B1 = 6.6 T). UFC
T (z) by FCM under the static
magnetic ﬁeld of 3 T at T = 48, 60, 70 and 77 K and UT (5 mm) by the MMPSC+IMRA
method for the u45 mm GdBaCuO bulk at Ts = 30 K [11] are also indicated.

3 T and at T = 48, 60, 70 and 77 K are also indicated. The UFC
T (z) value increased with decreasing operating temperature T. It should
be noted that the UT(z) value by the SPA+IMRA method at 40 K is
as high as the UFC
T (z) value by FCM under 3 T at T = 48 K. If the
FCM is operated under a static magnetic ﬁeld higher than 3 T, theUFC
T (z) values are expected to increase. Since there is a possibility
to make the bulk crash due to the hoop stress, we could not perform the FCM for B > 3 T at lower temperature. In Fig. 6, the UT(5 mm) value magnetized by the MMPSC+IMRA process at
Ts = 30 K for the u45 mm GdBaCuO bulk is also shown [11], on
which BT (z = 0 mm) = 4.33 T and BT (z = 5 mm) = 1.45 T were realized by the MMPSC method. However, the UT (z = 5 mm) value wasabout a half of that for the u65 mm bulk investigated in this study
due to the smaller diameter of the bulk. The multi pulse techniquesuch as the SPA+IMRA method is effective for the enhancement of
the UT value for the superconducting bulk as large as 65 mm indiameter, even though the BT value at the bulk center is not so
high.
In summary, the total trapped ﬂux UT(z) on the u65 mm GdBaCuO superconducting bulk has been investigated as a function

Acknowledgment
This work is supported in part by a Grant-in-Aid for ScientiﬁcResearch from the Ministry of Education, Culture, Sports, Scienceand Technology, Japan (No. 19560003).
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