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Physics Procedia 27 (2012) 168 – 171

ISS2011

Position dependence of irreversibility line on thin plate
Gd-Ba-Cu-O bulk superconductor
Tomoyuki Naito∗,a,b , Daiki Furutaa , Takahiro Arayashikia , Hiroyuki Fujishiroa,b ,Yousuke Yanagic , Yoshitaka Itohca Department of Materials Science and Technology, Faculty of Engineering, Iwate University, Morioka 020-8551, Japanb Soft-Path Engineering Research Center (SPERC), Faculty of Engineering, Iwate University, Morioka 020-8551, Japanc IMRA Material R&D Co. Ltd., Kariya 448-0032, JapanAbstract
We measured the proﬁles of the trapped ﬁeld, BT , on a thin Gd-Ba-Cu-O superconducting bulk plate with 45 mm indiameter and 2 mm in thickness magnetized by the pulsed ﬁeld, where Gd-Ba-Cu-O consists of a superconducting matrix
phase of GdBa2 Cu3 O7−δ and a nonsuperconducting secondary phase of Gd2 BaCuO5 . The vortices were mainly trappedat the periphery in the growth sector regions (GSRs) for low applied ﬁelds, and around the growth sector boundaries(GSBs) and under the seed crystal (SC) position for high applied ﬁelds. The irreversibility line, which was determinedfrom the resistivity measurements, of the sample cut from the GSR was rather lower than those of the samples cut fromthe GSBs and the SC position. This result revealed the weak vortex pinning strength in the GSRs and was consistent
with the BT proﬁles by PFM. The obtained results suggest that the resistivity can also probe the distribution of the vortex
pinning strength.
c 2012
2011 PublishedPublished by Elsevier Ltd.
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Selectionand/orand/orpeer-review
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Open access under CC BY-NC-ND license.

Keywords: Gd-Ba-Cu-O bulk; pulsed ﬁeld magnetization; trapped ﬁeld; irreversibility line; resistivity

1. Introduction
RE-Ba-Cu-O superconducting bulks (RE:rare earth elements), which consists of a superconducting
REBa2 Cu3 O7−δ and a nonsuperconducting RE2 BaCuO5 phases, can realize strong quasi-permanent magnets by trapping a large amount of vortices. A ﬁeld-cooled magnetization (FCM) is a preferable techniqueto maximize the trapped ﬁeld, BT , on the superconducting bulk, although a large and expensive superconducting solenoid coil magnet is needed. Pulsed ﬁeld magnetization (PFM) has been intensively studied,because the apparatus is compact and mobile. However, the magnitude of the BT by PFM is rather small
and inhomogeneous in comparison with that by FCM, which is caused by the large temperature rise dueto the dynamic motion of vortices [1]. Yanagi et al. reported that in the Sm-Ba-Cu-O bulk the vortices
were trapped mainly around the growth sector regions (GSRs) and the growth sector boundaries (GSBs),respectively, by applying low and high pulsed ﬁeld [2]. These results indicate that the BT by PFM depends∗ Corresponding author. Tel.: +81 19 621 6362; fax: +81 19 621 6362.

Email address: tnaito@iwate-u.ac.jp (Tomoyuki Naito)

1875-3892 © 2012 Published by Elsevier B.V. Selection and/or peer-review under responsibility of ISS Program Committee
Open access under CC BY-NC-ND license. doi:10.1016/j.phpro.2012.03.437

Tomoyuki Naito et al. / Physics Procedia 27 (2012) 168 – 171(a) FCM(b) PFM (Bex=1.1 T)(c) PFM (Bex=1.3 T)

Fig. 1. (a) Trapped ﬁeld proﬁle magnetized by FCM at 65 K. Trapped ﬁeld proﬁles magnetized by PFM at 60 K for (b)Bex =1.1 T and(c)Bex =1.3 T. The broken lines represent the growth sector boundaries (GSBs) and the crossing point is the seed crystal (SC) position.

sensitively on both the critical current density, Jc , distribution and the magnitude of the pulsed ﬁeld. The
relationship between the BT proﬁle by FCM and the relative Jc distribution was successfully explained byEisterer et al. using the magnetoscan method [3], where the absolute value of Jc was not reported. Recently,Fujishiro et al. showed that the BT proﬁles of the Gd-Ba-Cu-O thin bulk plate magnetized by PFM depended mainly on the Jc distribution which was directly evaluated by the magnetization measurement using
the small pieces cut from the thin bulk plate [4].
In this paper, we examine the irreversibility lines determined from the resistivity measurements using
the identical samples cut from the thin Gd-Ba-Cu-O plate and discuss a possibility of the resistivity as aprobe for the vortex pinning strength.
2. Experimental procedureThin plate of Gd-Ba-Cu-O bulk with 45 mm in diameter and 2 mm in thickness was sliced from thetop surface of the 15 mm thick bulk [5] grown by a top-seeded melt-texture technique using a Nd-BaCu-O seed at Superconductivity Research Laboratory, ISTEC, Japan. The thin plate was mounted tightly
on the cold head of a Giﬀord-McMahon (G-M) type helium refrigerator with a 1 mm stainless steel capfor both PFM and FCM measurements. In the PFM, the copper solenoid coil was set outside the vacuum
chamber and was cooled using the liquid nitrogen. The thin plate was cooled down to a target temperatureby zero-ﬁeld cooling and then a pulsed ﬁeld was applied with a rise time of 12 ms and duration of 100 ms.
Two dimensional (2-D) BT proﬁle was taken at a distance of 1 mm from the plate surface by scanning acryogenic axial-type Hall probe (BHA-921, F.W. Bell Inc.). In the FCM, the plate was cooled down to thetarget temperature in the magnetic ﬁeld of 1.5 T generalized by a cryo-cooled superconducting solenoid
magnet (JMTD-10T100, JASTEC Inc.), kept for 10 min, and ﬁnally the applied ﬁeld was decreased to zeroat a rate of 3 mT/s. 2-D BT proﬁle for the FCM was measured on the vacuum chamber at a distance of
4 mm from the plate surface. For the resistivity measurements, the thin plate was cut into small pieces witha typical size of 1 × 1 × 2mm3 after the PFM and FCM measurements. We measured two pieces cut fromthe GSBs (GSB-#1 and #2), one piece from the SC position (SC-#1) and another from the GSR (GSR-#1).
Resistivity was measured by a conventional dc four probe method with a typical current density of 5 A/cm2
in magnetic ﬁelds parallel to the c-axis up to 10 T.
3. Results and Discussion
Fig. 1(a) shows the BT proﬁle by FCM at 65 K 4 mm above the bulk surface. The proﬁle is nearlyhomogeneous and whose maximum appears around the center of the thin plate. The broken lines represent
the GSBs and the crossing point corresponds to the SC position at the crystal growth. Figs. 1(b) and 1(c)

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Tomoyuki Naito et al. / Physics Procedia 27 (2012) 168 – 171

1010-110-210-3GSB-#10T
0.5 T
1T
3T
5T
7T
10 T

758085T(K)90

1010-110-210-370-110-21008075

85T(K)

90

95

10080

85
T(K)

90μ0H(||c)

10010-1(c)75(b)

SC-#10T
0.5 T
1T
3T
5T
7T
10 T

GSB-#20T
0.5 T
1T
3T
5T
7T
10 T

70

ρ/ρ(100 K) (arb. unit)ρ/ρ(100 K) (arb. unit)

μ0H(||c)95

μ0H(||c)010(a)

70010ρ/ρ(100 K) (arb. unit)ρ/ρ(100 K) (arb. unit)

μ0H(||c)07095

100GSR-#10T
0.5 T
1T3T5T
7T
10 T(d)758085T(K)9095

100Fig. 2. Temperature dependence of the reduced resistivity , ρ(T )/ρ(100 K), of the small pieces samples in magnetic ﬁelds parallel tothe c-axis up to 10 T, where ρ(100 K) is the resistivity at 100 K.

show the BT proﬁles at 60 K by PFM 1 mm above the bulk surface after applying pulsed ﬁeld, Bex , of1.1 T and 1.3 T, respectively. For Bex =1.1 T, the vortices are trapped mainly around the periphery in theGSRs and do not intrude into the center. On the other hand, the vortices penetrate into the center and aretrapped mainly around the GSBs and SC position for Bex =1.3 T. The inclined elliptic BT proﬁle indicatesthe inhomogeneous distribution of the vortex pinning strength and the temperature rise.
Fig. 2 presents the temperature dependence of the reduced resistivity, ρ(T )/ρ(100 K), of the small pieces
in magnetic ﬁelds parallel to the c-axis up to 10 T, where ρ(100 K) is the resistivity at 100 K. The criticaltemperature, T c , is about 94 K for all the samples, demonstrating high quality and homogeneous superconductivity. The transition temperature in the magnetic ﬁeld decreases with increasing magnetic ﬁeld andthe resistive broadening of GSR-#1 is somewhat larger than those of other samples. The irreversibility
temperature, T irr , is deﬁned at the temperature in ρ(T )/ρ(100 K)=0.2. Fig. 3 shows the magnetic-ﬁeld vs.
temperature diagram. The irreversibility line, Hirr (T ), of GSR-#1 is located obviously at lower temperatureand magnetic-ﬁeld, in comparison with those of GSB and SC samples, which suggests that the vortex pinning in GSR is weaker than those of GSBs and SC and is consistent with the BT proﬁles by PFM. The Hirrline of the SC-#1 is slightly lower than those of GSB samples, which might originate from the fact that theamount of pinning centers such as Gd2 BaCuO5 (Gd211) particles decreases at the position far from the SC
because of the pushing eﬀect. Since the current density using the resistivity measurement corresponds to thecritical current density, Jc , the Hirr (T ) line represents the isothermal Jc =5 A/cm2 one in this study. Although

Tomoyuki Naito et al. / Physics Procedia 27 (2012) 168 – 171

1210Hirr(T)μ0H (T)

86
42

GSB-#1
GSB-#2
SC-#1
GSR-#10
0.8

0.9

11-T/TcFig. 3. The phase diagram of magnetic-ﬁeld vs. reduced temperature. The irreversibility lines determined from the resistivity measurements are shown.

this Jc value is about four orders of magnitude smaller than that determined from the magnetization loop [4],the relationship between the BT proﬁles by PFM and the Hirr (T ) lines suggests that we can use the resistivity
measurement as a probe to estimate the distribution of vortex pinning strength.
4. Summary
We measured the trapped ﬁeld, BT , proﬁles on a φ45 mm Gd-Ba-Cu-O superconducting bulk platewith 2 mm in thickness magnetized by PFM and examined the relationship between the BT proﬁles andthe irreversibility lines determined from the resistivity measurements. The BT proﬁles suggested that thevortices were trapped mainly the periphery in the GSRs for lower applied magnetic pulse and around theGSBs and SC for higher applied ﬁeld. The irreversibility line of the sample cut from the GSR was lower
than those in the GSBs and SC. This is consistent with the BT proﬁles by PFM, although the Jc in theresistivity measurement is generally about three to four orders of magnitude smaller than that determinedby the magnetic hysteresis loop. The results suggest that we can probe the vortex pinning properties by theresistivity measurements.
Acknowledgement
This work was supported in part by a Grant-in-Aid for Scientiﬁc Research (C) from JSPS, Japan (Nos.
20560001 and 23560002).
References[1] Fujishiro H, Hiyama T, Miura T, Naito T, Nariki S, Sakai N, Hirabayashi I 2009 IEEE Trans. Appl. Supercond. 2009;19;3545[2] Yanagi Y, Itoh Y, Oka T, Ikuta H, Mizutani U Supercond. Sci. Technol. 2005;18;839[3] Eisterer M, Haindl S, Wojcik T, Weber H W Supercond. Sci. Technol. 2003;16;1282[4] Fujishiro H, Naito T, Furuta D, Arayashiki T, Yanagi Y, Itoh Y Supercond. Sci. Technol. 2011;24;105003[5] Nariki S, Sakai N, Murakami M Supercond. Sci.Technol. 2005;18;S126171