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Trapped Field Profiles on Square GdBaCuO Bulks with Different Arrangement of Growth
Sector Boundaries

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2012 Jpn. J. Appl. Phys. 51 093005(http://iopscience.iop.org/1347-4065/51/9R/093005)
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REGULAR PAPER

Japanese Journal of Applied Physics 51 (2012) 093005
http://dx.doi.org/10.1143/JJAP.51.093005

Trapped Field Profiles on Square GdBaCuO Bulks with Different Arrangementof Growth Sector Boundaries
Hiroyuki Fujishiro1 , Takahiro Arayashiki1 , Takuya Tamura1 , Tomoyuki Naito1 ,Hidekazu Teshima2 , and Mitsuru Morita2
1
2

Faculty of Engineering, Iwate University, Morioka 020-8551, Japan
Advanced Technology Research Laboratories, Nippon Steel Corporation, Futtsu, Chiba 293-8511, Japan

Received June 3, 2012; accepted June 25, 2012; published online August 28, 2012
Square GdBaCuO bulks with 45:2  45:2 mm2 in the ab-plane and 15 mm in thickness along the c-axis with different arrangements of growth
sector boundaries (GSBs) were magnetized by a field-cooled magnetization (FCM), a zero-field cooled magnetization (ZFC), and a pulsed-fieldmagnetization (PFM) and the trapped field profiles were measured. For the lower applied field in ZFC, the magnetic flux was trapped in the growth
sector regions (GSRs), independent of the arrangement of GSBs. For the lower applied field in PFM, the magnetic flux was mainly trapped in the
GSRs and an additional flux was also trapped at the sides in both bulks because of the complicated flux intrusion by the local heat generation.
These bulks can trap a magnetic field as high as 7.5 T at 50 K by FCM without destruction. The magnetic flux intrusion and trapping for the squarebulks were discussed. # 2012 The Japan Society of Applied Physics

1. Introduction

REBaCuO superconducting bulks (RE: rare earth element
and Y) are used as conductors with zero resistance for power
current leads, as levitation devices using a pinning eﬀect,
and as high-strength bulk magnets using a strong pinning
force.1) To magnetize the bulk as a strong quasi-permanent
magnet, ﬁeld-cooled magnetization (FCM) using a superconducting coil magnet (SM) is a usual technique and canmaximize the trapped ﬁeld. Disk-shaped REBaCuO bulks
are commonly used for basic study and practical applications. Many research groups have extensively investigated
the trapped magnetic ﬁeld behavior in bulk superconductors.2–6) Square or rectangular bulks have also been
fabricated and used for speciﬁc applications such as aﬂywheel,7) magnetic bearings,8) and a magnetic separation
system.9) We have developed a bulk magnet system with
ﬁve-aligned square REBaCuO bulks, which has been used
for magnetic separation to purify waste water.10,11) The
square bulk is grown from an identical-shaped precursor,12)
or is cut from a disk bulk.13) The inﬂuences of the shape ofthe bulk and the arrangement of growth sector boundaries(GSBs) on the ﬂux intrusion path, the trapped ﬁeld proﬁle,and the mechanical strength have not been investigated,compared with the disk bulk.
As magnetizing methods for the REBaCuO bulks otherthan FCM, there are zero-ﬁeld cooled magnetization (ZFC)
and pulsed-ﬁeld magnetization (PFM). In the ZFC technique, the magnetic ﬁeld is applied and decreased using
SM on the cooled bulk lower than Tc , which is not a popular
technique to magnetize the bulk because only half of theapplied ﬁeld can be trapped at the center of the disk bulk.14)
On the other hand, the PFM technique has been intensively
studied because of the inexpensive and mobile experimental
setup without the use of SM. Several approaches have been
performed and have succeeded in enhancing the trapped
ﬁeld including by an iteratively magnetizing pulsed-ﬁeld
method with reducing amplitude (IMRA),15) and a multipulse technique with step-wise cooling (MPSC).16) A twostage PFM technique, named a modiﬁed MPSC (MMPSC),
was proposed by us,17) in which a record-high trapped ﬁeld
E-mail address: fujishiro@iwate-u.ac.jp

Fig. 1. Schematic view of two square-shaped bulks used in this study. In
the Bulk(+), GSBs are positioned crosswise to the bulk, and in the Bulk(),GSBs are positioned diagonally to the bulk.

of 5.20 T was realized on the disk-shaped GdBaCuO bulk
45 mm in diameter at 30 K.18) When the square bulk with
diﬀerent arrangements of GSBs is magnetized by PFM,
diﬀerent behaviors for the magnetic ﬂux intrusion and theﬁeld trapping proﬁle are supposed, compared with those fora disk-shaped bulk, because the distance of the ﬂux intrusion
path between the bulk periphery and the bulk center is not
identical at each position in the square bulk.
In this study, we magnetized the square bulks with
diﬀerent arrangements of GSBs by FCM, ZFC, and PFM
and compared the trapped ﬁeld proﬁles. The ﬂux intrusion
and the ﬂux trapping in the square bulk with diﬀerent
arrangements of GSBs are discussed.
2. Experimental Procedure

Two square-shaped GdBaCuO bulks (Nippon Steel) wereused with an area of 45:2  45:2 mm2 in the ab-plane and15 mm in thickness along the c-axis, which were cut froma disk-shaped bulk 65 mm in diameter. The bulk crystals
were composed of GdBa2 Cu3 O7 (Gd123) and Gd2 BaCuO5(Gd211) with the molar ratio of Gd123 : Gd211 ¼
0:75 : 0:25, 10 wt % Ag2 O, and a small amount of Pt
powder. Figure 1 shows a schematic view of the two squarebulks used in this study, where the dotted lines showed the
GSBs. In Fig. 1(a), GSBs are positioned crosswise to thebulk. Hereafter, we abbreviate this conﬁguration as Bulk(+).
In Fig. 1(b), GSBs are positioned diagonally to the bulk,
where we abbreviate this conﬁguration as Bulk(). The
bulks were tightly mounted in a stainless (SUS316L) frame
5 mm in thickness using a Stycast 2850GT resin.

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Jpn. J. Appl. Phys. 51 (2012) 093005

H. Fujishiro et al.

12

110
FCM

Bulk (+), T =48K
s

10

100

B (T)

80
6
70
4

Bex

2
0

Fig. 2. Experimental setup for (a) FCM and ZFC and (b) PFM around thebulk and the magnetizing coil.

Figure 2(a) shows the experimental setup for FCM
and ZFC. The bulk was mounted tightly on the cold stageof a Giﬀord–McMahon (GM) cycle helium refrigerator.
For FCM, the magnetic ﬁeld of 10 T was reduced to zeroat 0:224 T min1 at the temperature of the bulk, Ts ¼
48{80 K, using a cryo-cooled superconducting solenoid
magnet (JASTEC JMTD-10T100). For ZFC, the magnetic
ﬁeld was increased at 0.224 T min1 at Ts ¼ 77 K, was kept
at the maximum ﬁeld of Bex ¼ 1 T for 15 min, and thenreduced to 0 T at the same speed. Two-dimensional trapped
ﬁeld proﬁles, Bz FCM (4 mm) and Bz ZFC (4 mm), were measured on the vacuum sheath surface at a distance of z ¼ 4 mmfrom the bulk surface, stepwise with a pitch of 1 mm byscanning an axial-type Hall sensor (F W Bell, BHA 921).
The time dependences of the local magnetic ﬁelds BL C ðtÞ
and temperatures T ðtÞ were measured, respectively, using
the Hall sensor (F W Bell, BHT 921) and the Cernox
thermometer, both of which were adhered on the center ofthe bulk surface.
Figure 2(b) presents the experimental setup for PFM. The
bulk was tightly set on a soft iron yoke cylinder 60 mm
in diameter and 20 mm in thickness and mounted similarlyon the refrigerator. The magnetizing solenoid copper coil,which was cooled using liquid nitrogen, was placed outside
the vacuum chamber. A single magnetic pulse Bex with anamplitude from 2.5 to 6.4 T and with a rise time of 0.01 s
and a duration of 0.1 s was applied to the bulk, which wascooled to Ts ¼ 40 or 77 K. The trapped ﬁeld proﬁles of
Bz PFM (1 mm) were mapped at a distance of z ¼ 1 mm above
the bulk surface, stepwise with a pitch of 1 mm by scanning
the Hall sensor (BHA 921) inside the vacuum chamber using
an x–y stage controller. We cannot measure the trapped ﬁeld
proﬁles for PFM and ZFC/FCM under an identical distance,z, from the top surface of the bulk because of the limitationof the experimental apparatus.
3. Results and Discussion
3.1 Field-cooled magnetization

Figure 3 shows examples of the time dependence of theapplied ﬁeld Bex ðtÞ, the local ﬁeld BL C ðtÞ at the center ofthe bulk surface, and temperature T ðtÞ on the Bulk(+) at
Ts ¼ 48 K for FCM. During the descending stage for t 

B
0

60

T

C

50

L

100

T (K)

90

8

200
Time (min)

300

40
400

Fig. 3. (Color online) Time dependence of applied ﬁeld Bex ðtÞ, local ﬁeld
BL C ðtÞ, and temperature T ðtÞ on the Bulk(+) magnetized by FCM at 48 K.

Fig. 4. (Color online) Temperature dependence of (a) trapped ﬁeld Bz

and (b) maximum temperature rise Tmax on the Bulk(+) and Bulk()magnetized by FCM.

300 min, the temperature increased by about 6 K graduallyand then recovered to the initial temperature. The local
ﬁeld BL C ðtÞ decreased from 10 T gradually, and ﬁnally, themagnetic ﬁeld of Bz ¼ 7:65 T was trapped on the center ofthe bulk surface.
Figures 4(a) and 4(b) present, respectively, the trapped
ﬁeld Bz and the maximum temperature rise Tmax for theBulk(+) and Bulk() during FCM, as a function of Ts .
The Bz and Tmax for each bulk increased monotonicallywith decreasing Ts and a small amount of the diﬀerence
between two bulks can be detected, which may result fromtheir performance diﬀerences such as local variation in
Jc , critical temperature Tc , macrocracks or Ag particles, orsome relationship with the GSB arrangement. However,note that the square GdBaCuO bulk with an area of 45:2 
45:2 mm2 can trap over 7.5 T at approximately 50 K without
destruction, and Bz is independent of the arrangement of
GSBs.
Figures 5(a) and 5(b) show the trapped ﬁeld proﬁles
Bz FCM (4 mm) for the Bulk(+) at Ts ¼ 48 K and Bulk()at Ts ¼ 52 K magnetized by FCM. The trapped ﬁeld proﬁlesshow the pyramidal proﬁles, which do not depend on
the arrangement of GSBs. These results indicate that the093005-2# 2012 The Japan Society of Applied Physics

Jpn. J. Appl. Phys. 51 (2012) 093005

H. Fujishiro et al.

Fig. 5. (Color online) Trapped ﬁeld proﬁles Bz FCM (4 mm) on the square-shaped bulk of (a) Bulk(+) and (b) Bulk() magnetized by FCM.

Fig. 6. (Color online) Trapped ﬁeld proﬁles Bz ZFC (4 mm) of (a) Bulk(+)
and (b) Bulk() after the ZFC of Bex ¼ 1 T at 77 K.

diﬀerence in the arrangement of GSBs cannot be detectedby the trapped ﬁeld proﬁles by FCM in the square bulk.
However, in the disk bulk, trapped ﬁeld proﬁles show
conical proﬁles,2–6) in which the arrangement of GSBs was
detected by the trapped ﬁeld proﬁles by FCM.

2.0

PFM

BzPFM (T)3.2 Zero-field cooled magnetization

Figures 6(a) and 6(b) present, respectively, the trapped ﬁeld
proﬁles Bz ZFC (4 mm) for the Bulk(+) and the Bulk()at 77 K after the ZFC of Bex ¼ 1:0 T. For an applied ﬁeld
as low as 1.0 T, where the magnetic ﬂux can intrude
only around the bulk periphery, a clear diﬀerence in theBz ZFC (4 mm) proﬁles can be seen between two bulks. In the
proﬁle of the Bulk(+) as shown in Fig. 6(a), the magnetic
ﬂux intruded and was trapped preferentially at the growth
sector regions (GSRs), that is, at the corners of the square.
GSRs mean the regions enclosed by GSBs. On the other
hand, in the proﬁle of the Bulk() as shown in Fig. 6(b), themagnetic ﬂux was also trapped preferentially at the GSRs,
that is, at the sides of the square. The critical current density
Jc in GSRs is generally lower than that in GSBs and it isdiﬃcult for the ﬂux to intrude and trap into the GSBs
area for a lower Bex .19) Note that the trapped ﬁeld proﬁlesmagnetized by ZFC are useful to conﬁrm the Jc distribution(or the pinning force distribution) around the bulk peripheryvisually. In the experiment of ZFC, the temperature rise wasas small as 0.1 K.

Bulk(+) at 77K
Bulk(x) at 77K
Bulk(+) at 40K
Bulk(x) at 40K

1.5

1.0

0.5

0

0

1

2

3
B

ex

4
(T)

5

6

7

Fig. 7. (Color online) Trapped ﬁeld Bz PFM (1 mm) at the center of the bulk

surface on the Bulk(+) and Bulk() as a function of applied pulsed ﬁeld Bex
at 40 and 77 K.

3.3 Pulsed field magnetization

Figure 7 shows the trapped ﬁeld Bz PFM (1 mm) at the centerof the bulk surface on the Bulk(+) and Bulk(), as a function of applied pulsed ﬁeld Bex at 40 and 77 K. At Ts ¼ 77 K,
the magnetic ﬂux starts to intrude and trap at Bex ¼
2:5{3:0 T and Bz PFM (1 mm) increases and takes a maximum
at Bex ¼ 4:5 T. At Ts ¼ 40 K, the magnetic ﬂux starts to093005-3# 2012 The Japan Society of Applied Physics

Jpn. J. Appl. Phys. 51 (2012) 093005

H. Fujishiro et al.

Fig. 8. (Color online) Trapped ﬁeld proﬁles Bz PFM (1 mm) of the Bulk(+) and Bulk() at Ts ¼ 40 K for typical applied pulsed ﬁelds Bex .

intrude and trap at 4 T and Bz PFM (1 mm) increases monotonically with increasing Bex up to 6.4 T. The shift of Bex 0 , atwhich the magnetic ﬂux starts to intrude and trap, resultsfrom the increase in the Jc with decreasing temperature.
These Bz PFM (1 mm) vs Bex characteristics are a common
feature of PFM.20) The diﬀerence in the characteristics
between the Bulk(+) and Bulk() is very small, but thesuperconducting properties of the Bulk(+) seem to beslightly better than those of the Bulk().
Figure 8 shows the trapped ﬁeld proﬁles Bz PFM (1 mm) of
the Bulk(+) and Bulk() at Ts ¼ 40 K for typical applied
pulsed ﬁelds Bex . For a lower applied ﬁeld around Bex ¼ 4 T,
as shown in Figs. 8(a) and 8(b), the diﬀerences in the
Bz PFM (1 mm) proﬁles can be seen between two bulks. Thatis, in the Bulk() shown in Fig. 8(b), the magnetic ﬂux was
preferentially trapped at the GSRs except for the right GSR
region. On the other hand, in the Bulk(+) shown in Fig. 8(a),the magnetic ﬂux was also trapped at the sides of the bulk aswell as that at the GSRs. These results do not always show
consistency with those obtained by ZFC as shown in Fig. 6,
although ZFC can be regarded as a kind of PFM techniquein which the duration of the applied magnetic pulse is aslong as 100–1000 s. The temperature rise during PFM islarger than that during ZFC owing to the fast motion of
the magnetic ﬂux.21) Since the distance from the sides tothe center is shorter than that from the corner to the centerin the Bulk(+), it is easy for the magnetic ﬂux to penetratefrom the sides of the square bulk, even though the GSRs
with lower Jc are positioned diagonally in the bulk. The
diﬀerence in the length of GSBs may explain these phe-nomena. For a higher applied ﬁeld of Bex ¼ 6:3 T, as shownin Figs. 8(c) and 8(d), the diﬀerences in the Bz PFM (1 mm)
proﬁles are small between two bulks. However, strictly
speaking, the magnetic ﬂux seems to be trapped preferentially on the GSBs in the Bulk().
4. Conclusion

We magnetized square GdBaCuO bulks with an area of
45:2  45:2 mm2 in the ab-plane and 15 mm in thickness
along the c-axis with diﬀerent arrangements of GSBs by a
FCM, a ZFC, and a PFM and measured the trapped ﬁeld
proﬁles. A summary of important results and conclusions
obtained in this study is presented below.
(1) These bulks can trap the magnetic ﬁeld over 7.5 T
at 50 K by FCM without destruction. The trapped
ﬁeld proﬁles are pyramidal and the diﬀerence in thearrangement of GSBs cannot be detected using the
proﬁles obtained by FCM.
(2) For the lower applied ﬁeld for ZFC, the magnetic ﬂux
was mainly trapped in the GSRs, independent of thearrangement of GSBs in the square bulk. The trapped
ﬁeld proﬁles magnetized by ZFC are useful to conﬁrm
the Jc distribution or local variations in Tc (Gd/Ba
solid solution) or microcracks or Ag particles aroundthe bulk periphery visually.
(3) For the lower applied ﬁeld for PFM, the magnetic ﬂux
was mainly trapped in the GSRs for both arrangementsof GSBs and additional ﬂux was also trapped at thesides in both bulks because of the complicated ﬂux
intrusion caused by the local heat generation.

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Jpn. J. Appl. Phys. 51 (2012) 093005

H. Fujishiro et al.
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Acknowledgment

This work is supported in part by a Grant-in-Aid for
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# 2012 The Japan Society of Applied Physics