INSTITUTE OF PHYSICS PUBLISHING

SUPERCONDUCTOR SCIENCE AND TECHNOLOGYSupercond. Sci. Technol. 18 (2005) 158–165

doi:10.1088/0953-2048/18/1/025

Generated heat during pulse fieldmagnetizing for REBaCuO (RE = Gd,
Sm, Y) bulk superconductors withdifferent pinning abilities
Hiroyuki Fujishiro1 , Masahiko Kaneyama1 , Kazuya Yokoyama2 ,Tetsuo Oka2 and Koshichi Noto2
1
2

Faculty of Engineering, Iwate University, 4-3-5 Ueda, Morioka 020-8551, Japan
Iwate Industrial Promotion Center, 3-52-2, Iioka-shinden, Morioka 020-0852, Japan

E-mail: fujishiro@iwate-u.ac.jp

Received 24 May 2004, in final form 3 September 2004
Published 23 November 2004
Online at stacks.iop.org/SUST/18/158
Abstract
Pulse field magnetizing (PFM) using five successive magnetic pulses(Nos 1–5) with the same amplitude from 3.01 to 5.42 T has been performed
for three types of cryo-cooled REBaCuO bulk superconductor discs(RE = Gd, Sm, Y) with an identical size. The time evolution and spatial
distribution of temperature T (t), the total trapped magnetic flux PT and thetrapped magnetic field BTP have been measured after applying the magnetic
pulse. The total magnetic flux FC
T trapped by the field cooled magnetizing(FCM) is the largest for the Gd bulk and is the smallest for the Y bulk. The
time and position dependences of T (t) during PFM show a characteristic
behaviour depending on the species of bulks which results from thedifference in the strength of the pinning force Fp . The generated heat
Q(No i ) after the No i pulse has been estimated based on the maximum
temperature rise Tmax and the specific heat C. The
Q = Q(No 1)–Q(No 5) value, which is mainly contributed by thepinning power loss (Q p ) for pulse No 1, is the smallest for the Y bulk, andthe Q(No 5) value, which is mainly contributed by the viscous flow loss
(Q v ), is the smallest for the Gd bulk. These results suggest that the heatgeneration by PFM is closely related to the strength of Fp of the bulk crystal.

1. Introduction
As is well known, the critical current density Jc and the trappedmagnetic field BT of REBaCuO bulk superconductors (RE:rare earth element) are determined by the species of the RE
element and the content, the particle size and the dispersionof the RE2 BaCuO5 non-superconducting phase acting as apinning centre for the magnetic fluxes [1]. The BT value or the
total trapped magnetic flux T of the bulks has been enhancedby the improvement of the fabrication processes [2, 3]. For
practical applications of the bulk superconductors as a strong
bulk magnet for the magnetic separation, magnetic levitationand so on [4, 5], it is important to improve the mechanical0953-2048/05/010158+08$30.00 © 2005 IOP Publishing Ltd

and thermal properties besides Jc and BT . Tomita et al [6]realized the trapped magnetic field of 17.24 T at 29 K ina YBaCuO bulk by field cooled magnetizing (FCM) from
17.9 T to zero. They used two key technologies; one is
the mechanical reinforcement by resin impregnation, and theother is the thermal conduction enhancement by impregnating
the highly thermally conductive alloy into the small drilledhole. In addition to the FCM method, pulse field magnetizing(PFM) has been recently investigated and developed in order tostrongly magnetize the bulk superconductors [7]. Mizutani’sgroup proposed a novel PFM method of iterative magnetizing
operations with gradually reducing amplitudes, named the
IMRA method [8, 9]. It was demonstrated that, by the IMRA

Printed in the UK

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Generated heat during PFM for REBaCuO (RE = Gd, Sm, Y) bulks

method, the YBaCuO bulk could trap almost the same amountof the magnetic flux as the FCM method in liquid nitrogen [7].
At temperatures lower than 77 K, however, the maximum valueof BT and T by PFM including the IMRA method is generally
lower than that by FCM as reported for the SmBaCuO bulk
superconductors with the stronger pinning force Fp [8, 9]. A
possible reason may be a large temperature rise caused by themagnetization hysteresis loss and by the viscous loss due to themagnetic flux motion in a short pulse field period, which resultsin the decrease of BT . The realization of the trapped magnetic
field by PFM below 77 K ranking with FCM is greatly desired
because the cryo-cooled refrigerator is now very popular tocool bulk superconductors instead of liquid nitrogen.
We have studied the time evolution and spatial distributionof the temperature rise T (t) at the surface of the cryo-cooled
YBaCuO [10] and SmBaCuO [11, 12] bulk superconductors
after PFM. The T (t) behaviour changed depending on theinitial stage temperature Ts , the applied pulse field Bex andthe distribution of BT before applying the pulse field. The
measurement on the spatial distribution of T (t) enabled us
to locate the easy path through which the fluxes preferentiallyintrude into the bulk. We have estimated the generated heat Q
during PFM using T and the specific heat C [13].
The bulk superconductors with a stronger Fp generally
result in a higher Jc and consequently show a higher BT .
The bulks with a higher BT are expected to show a larger
pinning loss Q p . The temperature measurements and the
Q estimation during PFM for the bulk superconductors withvarious BT and Jc characteristics give us valuable information
for pinning power loss Q p and the viscous flow loss Q v . In
this paper, we report the time and position dependences ofT (t), the trapped field BTP and the trapped magnetic flux
PT after applying the five successive pulse fields (No 1–
No 5) ranging from Bex = 3.01 to 5.42 T for the cryo-cooled
REBaCuO bulk superconductors (RE = Gd, Sm, Y). From themeasured maximum temperature rise Tmax and the specificheat C for each bulk, the generated heat Q is calculated andthe contribution of Q p and Q v to the total Q are discussed. We
also discuss the relation between PT and the heat generation.

2. Experimental details
Three types of highly c-axis oriented REBaCuO bulk
superconductor discs on a commercial base were used inthis study, which had the same size, 45 mm in diameterand 15 mm in thickness. The GdBaCuO bulk, fabricated by
Nippon Steel Corporation Ltd, is composed of GdBa2 Cu3 O y(Gd123) and Gd2 BaCuO5 (Gd211) with the molar ratioof Gd123:Gd211 = 1.0:0.4, 10.0 wt% Ag2 O powder and
0.5 wt% Pt powder. Hereafter, we abbreviate this bulk as
the Gd bulk. The SmBaCuO bulk (Sm bulk), fabricatedby Dowa Mining Co., Ltd, is composed of SmBa2 Cu3 O y(Sm123) and Sm2 BaCuO5 (Sm211) with the molar ratioof Sm123:Sm211 = 1.0:0.3, 15.0% Ag2 O powder and0.42 wt% Pt powder. The YBaCuO bulk (Y bulk), fabricatedby Dowa Mining Co., Ltd, is composed of YBa2 Cu3 O y(Y123) and Y2 BaCuO5 (Y211) with the molar ratio of
Y123:Y211 = 1.0:0.4, 15.0 wt% Ag2 O powder and 0.42 wt%
Pt powder. These bulks were uniformly impregnated by epoxy
resin in vacuum. The epoxy resin layers on both upper andP1(T1)(a)P0(T0)Hall sensor(PH)
P2(T2)

P4(T4)GSB
P3(T3)

Growth sector
boundary(GSB)

Growth sector region (GSR)(b)

Figure 1. (a) The positions for the temperature and trapped fieldmeasurements on the surface of the REBaCuO bulk disc with thesame size (45 mm in diameter, 15 mm in thickness). P0–P4 for thetemperature measurements of T 0–T 4 are indicated. The trappedfield BT on the bulk surface is measured using an adhered Hallsensor at PH. (b) An example of the time dependence of the pulse
current I (t) which flows through the pulse coil for Bex = 3.01 T.

lower sides of the bulk were removed in order to measure
the precise temperature on the bulk surface and to reduce
the thermal contact resistance between the bulk and the cold
stage. Figure 1(a) shows the positions for the temperature
measurement on the bulk, which was tightly stuck on thesapphire plate (45 mm in diameter and 20 mm in thickness)
attached to the cold stage of a Gifford McMahon (GM) cycle
helium refrigerator (AISIN, GR103) using indium foil andwas evacuated below 10−5 Torr. The temperature rise dueto the eddy current in the Cu cold stage was reduced by theinserted sapphire plate between the stage and the sample andwas confirmed to be below 0.2 K at 100 K (>Tc ) for 5 T pulse
field. The initial stage temperature Ts was fixed at 40 K. The
temperatures T 0 at the centre of the bulk (P0) and T 1–T 4 at
P1–P4 in the four growth sector regions (GSRs) were measured
by chromel–constantan thermocouples (76 µm in diameter)
adhered to the bulk surface using GE7031 varnish. P1–P4
were situated on the central lines of each GSR, 9 mm apartfrom P0. Each temperature was measured about 7 times s−1
just after applying the pulse field.
The bulk crystals were magnetized using a pulse coil
(L = 1.08 mH) dipped in liquid N2 . Figure 1(b) shows
an example of the time dependence of the pulse current I (t)which flows through the pulse coil for Bex = 3.01 T. The risetime of the pulse field was about 12 ms. The strength of thepulse field Bex (t) was calculated from I (t), which ranged from3.01 to 5.42 T. The field shielding effect due to the Cu cold159

H Fujishiro et al

T 0FC of the Gd bulk is the smallest and that of the Sm bulk
is the largest around 50 K. T 0FC increased and BTFC decreased
with the increase in the field decreasing rate as was described
elsewhere [14]. For these three bulk discs with a different Fp ,the time evolution of the temperatures T 0(t)–T 4(t), trappedmagnetic flux PT and trapped field BTP have been measured
after PFM as shown in the following subsection.
3.2. Temperature rise and trapped magnetic flux for Gd, Sm
and Y bulks by PFM

Figure 2. (a) The trapped total magnetic flux FC
T and (b) thetrapped field BTFC by field cooled magnetizing (FCM) for the
REBaCuO bulks (RE = Gd, Sm, Y) as a function of the maximum
temperature at the bulk centre (T 0max ).

stage is not important because of the rather large pulse risingtime and the inserted sapphire spacer. The trapped magnetic
field BTP just on the bulk was measured by the Hall sensor(F W Bell, model BHA 921) adhered to position PH witha 2.5 mm distance from P0 as shown in figure 1(a). The
total trapped magnetic flux PT and the distribution of thetrapped magnetic flux density BT3 mm was measured using anaxial type Hall sensor, which scanned 3 mm above the bulk
surface stepwise with a pitch of 1.2 mm. Five magnetic pulses
with the same amplitude Bex were applied sequentially andT (t), BTP and PT were measured at each stage. Hereafter weabbreviate the five pulses as No 1–No 5. The temperaturerise after applying the pulse field was recovered to the initial
temperature (Ts = 40 K) for 15–20 min. The trapped field BTFC
and the trapped magnetic flux FC
T by FCM were also measured
at several temperatures using the cryo-cooled superconducting
magnet in order to elucidate the maximum ability of flux
trapping for each bulk. During FCM, the static magnetic
field of 5 T was decreased to 0 T in 18 min (0.278 T min−1 ).
The temperature dependence of the specific heat C(T ) was
estimated by the thermal conductivity κ divided by the thermal
diffusivity α measured for parallelepiped samples with thesame composition as the bulk discs.

3. Results and discussion
FC
3.1. Trapped magnetic flux FC
T and trapped field BT by
FCM

Figures 2(a) and (b) show the trapped total magnetic flux FCTand the trapped field BTFC by FCM for each bulk, respectively,
as a function of the maximum temperature T 0max at the centreFC(P0) of the bulk. The FC
T and BT values increase withdecreasing temperature for all the bulks. Below 80 K, FC
T
and BTFC are the largest for the Gd bulk and become smaller for
Sm bulk and Y bulk in this order. The differences in FC
T and
BTFC for the three bulks should result from the difference in the
Jc and Fp values. The temperature rise T 0FC during the FCM
process is about 2–4 K at T 0max  50 K for the field decreasingrate of 0.278 T min−1 and decreases with increasing T 0max .
160

Figures 3(a) and (b) show the time evolutions of T 0(t)–T 4(t)for the Y bulk at Bs = 40 K after applying the No 1 andNo 5 pulse fields of 3.01 and 3.87 T, respectively. Figures 3(c)and (d) show the similar temperature changes for the Sm bulk
and figures 3(e) and (f) show those for the Gd bulk. The
inset for each figure shows the distribution of the trappedmagnetic flux density BT3 mm after applying pulse No 1. It canclearly be seen that the absolute value and the time evolutionof temperatures T 0(t)–T 4(t) for pulse No 1 depends on thespecies of the bulk. In figure 3(a) for the Y bulk, T 4(t) andT 1(t) rise first with Tmax  8 K, followed by T 2(t), T 0(t)and T 3(t) in this order for Bex = 3.01 T, which suggests that Fp
in GSR4 and GSR1 is relatively weak. Since the time profile ofT 0–T 4 is smooth and does not show a clear peak, the position
dependence of Fp may be small. The spatial dependence of the
maximum temperature rise Tmax is also small. The appliedfield of Bex = 3.01 T is high enough to destroy the pinningpotential barrier in the peripheral region. But the magnetic
flux does not reach the centre of the bulk sufficiently as shownin the distribution of BT3 mm . For Bex = 3.87 T in figure 3(b),the temperature rise increases (Tmax  18 K) and the time
profile of T 2(t), T 0(t) and T 3(t) becomes nearly identical.
The BT3 mm profile indicates that the flux penetrates into thebulk uniformly.
In figures 3(c) and (d) for the Sm bulk, on the other hand,
the time profile of temperature shows a large and clear peakin some GSRs. T 2(t) and T 3(t) rise first with a sharp peak(Tmax  16 K), followed by T 4(t) and T 1(t), and T 0(t)rise latest for pulse No 1, and then the temperatures approach
the initial temperature. The magnetic fluxes should penetrate
into the bulk crystal preferentially through the weaker pinning
regions. The magnetic flux easily intrudes into the Sm bulk
through the regions around P2 and P3, and the temperature riseT is more intense in these GSRs. The trapped field BT3 mm isalso enhanced around P2 and P3. For Bex = 3.87 T shown infigure 3(d), the temperature rises increase (e.g., Tmax  26 K
at T 3). The BT3 mm value increases and the BT3 mm profile
takes a cone shape. In figures 3(e) and (f) for the Gd bulk,
the temperature rises do not take place uniformly after pulse
No 1, similarly to the Sm bulk; the temperature rise is thelargest at T 3 (Tmax  10 K) for Bex = 3.01 T and at
T 1 (Tmax  24 K) for Bex = 3.87 T where Fp may berelatively small. In this way, the characteristic temperaturerises can be seen to depend on the species of the bulk crystal.
For the pulse field applications from No 2 to No 5 for each
Bex , the characteristic peak in T (t) of the Gd and Sm bulks
is completely wiped out and T decreases and then saturates.
In all cases of flux penetration, T 0(t) at the centre of the bulk
rises last because the heat is mainly generated in the peripheral

Generated heat during PFM for REBaCuO (RE = Gd, Sm, Y) bulks

Figure 3. The time evolutions of temperatures T 0(t)–T 4(t) at Ts = 40 K after applying the No 1 and No 5 pulse fields of (a) 3.01 T and (b)3.87 T for the Y bulk. (c) and (d) show similar results for the Sm bulk, and (e) and (f) for the Gd bulk. The inset for each figure shows the
distribution of the trapped magnetic flux density BT3 mm after applying pulse No 1.

region where the flux moves faster and the generated heatdiffuses toward the central region.
Figures 4(a) shows the pulse number dependence of theaverage temperature rise T for each bulk after applying thepulse field Bex (=3.01–4.64 T). T is defined by the averaged
value of the temperature rises of T 1–T 4 and the bar shows the
maximum and minimum temperature rise of T 1–T 4. In
all the cases, T monotonically decreases and approaches asteady value with increasing pulse number. T of the Sm bulk
is the largest for each pulse number and for each Bex . The

T values of the Y bulk after pulse No 1 are smaller thanthose of the Sm bulk but are similar to the Sm bulk after
pulse No 2. On the other hand, for the Gd bulk, T isthe smallest for each Bex . Since the temperature rise occurs
under the nearly adiabatic condition in the PFM process, thethermal contact resistance between the bulk disc and the cold
stage of a GM refrigerator hardly influences the maximum
temperature rise Tmax [10]. Figure 4(b) shows the pulse
number dependence of the difference of the temperature risedT = T (n − 1)− T (n) between the T after the (n − 1)th161

H Fujishiro et al

Figure 4. The pulse number dependence of (a) the averagetemperature rise T and (b) the difference of the temperature risedT between the T after the (n − 1)th and (n)th pulses.

Figure 5. The average temperature rise T of three bulks as afunction of the applied field Bex for pulses (a) No 1 and (b) No 5,
respectively.

and that after the (n)th pulses. The dT value drastically reduces
with the increase in the pulse number and then approaches
zero.
Figures 5(a) and (b) show the average T of three bulk
discs as a function of Bex for pulses No 1 and No 5, respectively.
In both figures, T increases with increasing Bex . However,the T –Bex curves for pulse No 1 are convex and those forpulse No 5 are concave. The T value of the Sm bulk is thelargest for pulse No 1 and that of the Gd bulk is the smallest
for pulse No 5.
162

Figure 6. The pulse number dependence of (a) the total trappedmagnetic flux PT and (b) the increment of the trapped flux dPT after
the preceding pulse.

Figure 6(a) shows the pulse number dependence of thetotal trapped magnetic flux PT of the three bulks for Bex =3.01–4.64 T. The largest amount of the fluxes is trapped
during application of pulse No 1 to the virgin state bulks.
PT is gradually enhanced with increasing pulse number,approaching a fixed ultimate value for pulses No 4 and No 5.
The increment of the trapped flux dPT (=PT (n) − PT (n − 1))
after the preceding pulse is presented in figure 6(b). The
intrusion and additional trap of the magnetic flux are reducedby the presence of the already trapped flux. These saturation
tendencies much resemble the behaviours of dT shown infigure 4(b). In figure 6(a), the PT value for Bex = 3.01 T
is the largest for the Sm bulk and the smallest for the Gd bulk.
For the Gd bulk, the pressure of the magnetic flux associatedwith a lower field cannot overcome the pinning potential barrierin the close vicinity of the surface region and the flux intrusion
is impeded by the surface pinning barrier. On the other hand,for the applied fields of 3.86 and 4.64 T, the PT value is thelargest for Gd bulk and is the smallest for Y bulk. This trend
is consistent with FC
T by FCM as shown in figure 2(a) andreflects the intrinsic pinning ability of each bulk.
Figures 7(a) and (b) show the trapped magnetic flux PTafter pulse No 1 and pulse No 5, respectively, as a function of
Bex . PT increases with increasing Bex for each bulk, shows amaximum and then decreases for Bex higher than 4.64 T. Thesetendencies can be understood on the basis of the FC
T –T 0max
line as shown in figure 2(a) [10, 11]. When the pulse fieldBex higher than 4.64 T is applied to the bulk at Ts = 40 K,

Generated heat during PFM for REBaCuO (RE = Gd, Sm, Y) bulks

Figure 7. The total trapped magnetic flux PT after (a) pulse No 1
and (b) pulse No 5 as a function of Bex .

Figure 8. The trapped magnetic flux BTP at the position PH in
figure 1 after (a) pulse No 1 and (b) pulse No 5 as a function of Bex .

T 0max of the bulk touches the FC
T –T 0max line owing to thelarger temperature rise and then FC
T decreases following theline. The larger temperature rise due to the violent flux motion
weakens the pinning force Fp and hinders the flux trapping at
this high level of Bex . Figures 8(a) and (b) show the trappedmagnetic field BTP for the application of pulse No 1 and pulse
No 5, respectively, as a function of Bex . Similarly to the PT
results, BTP shows a maximum around Bex = 4.64 T for all
bulks and then decreases with the further increase in Bex . BTP of
the Gd and Sm bulks is larger than that of the Y bulk. In all thebulks, BTP is very small for Bex = 3.01 T. This result suggeststhat applied magnetic flux cannot reach the centre of the bulk
but the trapped flux remains in the peripheral region as is seen
in each inset in figure 3. It is worthwhile to note that the BTP
value for the Gd bulk after the first (No 1) pulse application of
4.64 T is as high as about 3.40 T which is about 70% of the
BTFC value in figure 2(b).
3.3. Specific heat of bulk superconductors
We have measured the thermal conductivity κ(T ) and thethermal diffusivity α(T ) of the three types of parallelepipedsamples with the same composition as the bulk discs. κ(T )Figure 9. The temperature dependence of the estimated specificheat C(T ) for each bulk. The inset shows the ab-plane κab (T ) andc-axis κc (T ) thermal conductivities of the three bulks.

was measured by a steady-state heat flow method between
10 and 300 K and the α(T ) measurement was performed byan arbitrary heating method under an identical experimental
set-up with the κ measurement [15]. The specific heatC(T ) (J cm−3 K−1 ) was estimated from the relation C = κ/α,which is presented in figure 9 for each bulk. The inset infigure 9 shows the temperature dependence of the thermal
conductivity in the ab-plane (κab ) and along the c-axis (κc ).
The absolute values of κab (T ) and κc (T ) are the largest for
the Y bulk because of the higher Ag contents (=15 wt%) and,possibly, of the higher crystallinity compared with the Sm bulk,
in which the phonon scattering by the crystal defect may beenhanced due to the Ba–Sm inter-diffusion [16]. The absolutevalues of αab (T ) and αc (T ) were also the largest for the Y bulk
and the smallest for the Sm bulk. As a result, the specific heatC(T ) of each bulk is almost identical irrespective of the RE
element and somewhat different Ag content. Since the heatgeneration occurs under nearly an adiabatic condition during
the PFM process, the C(T ) value should directly decide thetemperature rise T . The thermal conductivity of the bulk
may affect the recovery time to the initial temperature and thetemperature rise TFC in the FCM process.
3.4. Estimation of generated heat Q
The generated heat Q due to the pulse field application can be
estimated using the following equation:
Q= Ts +Tmax

C(T )V dT ,

(1)

Ts

where V is the volume of the bulk disc, Ts is the bulk initial
temperature (= 40 K) and Tmax is the average maximum
temperature rise. Figures 10(a) and (b) show the results of the
Q(No 1) and Q(No 5) values after applying pulses No 1 andNo 5, respectively, as a function of Bex . Figure 10(c) shows theQ = Q(No 1)–Q(No 5) value as a function of Bex . The heatgeneration Q during PFM can be regarded as the sum of thepinning loss Q p and the viscous flow loss Q v [12]. Similarly toT in figure 4, the PT values also almost saturate after pulse
No 3 in figure 6. Accordingly, no additional flux trapping takes
place during pulse No 5. Then Q(No 5) shown in figure 10(b)163

H Fujishiro et al

Figure 10. The estimated Q values as a function of Bex . (a) The Q values after applying pulse No 1 (Q(No 1)), (b) the Q values after
applying pulse No 5 (Q(No 5)) which are regarded as the sum of the pinning loss Q sp uncorrelated with the flux trapping and the viscous flow
loss Q v , (c) the Q = Q(No 1)–Q(No 5) values which stand for the heat generation for pulse No 1, directly connected to the flux trapping.

is given by the sum of the saturated hysteresis pinning power
loss Q sp , which is not related to the flux trapping, and theviscous flow loss Q v . Then the Q value can be regarded
as the heat generation due to the flux trapping during the pulse
No 1 field, if we assume that the Q v and Q sp values are notmuch different for each pulse. It can be clearly seen that theQ value for the Y bulk is smaller than that for the Gd andSm bulks which may result from the smallest Fp in the threebulks.
Though the PT value of the Gd bulk shown in figure 7 islarger than that of the Sm bulk due to the stronger Fp , Q of
the Gd bulk is slightly smaller than that of the Sm bulk. As we
can see in figures 3(c) and (d), T 2(t) and T 3(t) of the present
Sm bulk rise quite rapidly and exhibit clear overshoots. This
unusual behaviour of T 2(t) and T 3(t) suggests that the flux
penetrates more easily along the easy paths containing or very
near the T 2 and T 3 measuring points. The flux penetration ina irregular manner and the rampant flux motion along the easy
paths may cause additional viscous loss Q v in this Sm bulk.
In figure 10(c), the Q value takes a maximum at 4.64 T
and decreases with the further increase in Bex . Q and thetrapped magnetic flux PT in figure 7(a) have very similar Bex
dependence; i.e., if Q is large, PT is also large. These results
support our assumption that Q can be roughly regarded as theheat generation correlated to the flux trapping. In figure 10(b),Q(No 5) is the smallest for the Gd bulk. The Gd bulk with thestrongest Fp should trap the magnetic fluxes more intensely. In
materials with stronger flux pinning centres, the flux motion ismore strongly impeded. Then the viscous flow may be reduced,
reducing the viscous flow loss as well.
The analyses of the magnetic and heat-loss behaviourof the bulk superconductor are desired to be performed
quantitatively, applying the Bean critical state model. The
Bean model describes the behaviour of the magnetic flux φT
but does not directly deal with the heat-loss. In this study, weonly measured the trapped flux PT and the trapped field BTP
after the pulse field application and the discussion cannot but
remain phenomenological. Simultaneous measurements of themagnetization M(t) during the pulse field and the temperature
T (t) are in progress and will be reported in a near future
together with more quantitative analyses.
164

4. Summary
The time evolution and the spatial distribution of temperatures
T (t) for three types of REBaCuO bulk superconductors(RE = Gd, Sm, Y) with different flux pinning abilities havebeen measured after five iterative pulse fields (Nos 1–5) withthe same amplitude (Bex = 3.01–5.42 T). The generated
heat Q has been estimated using the measured specific heatC(T ) and the maximum temperature rise Tmax . The relations
between the temperature rise T (t), the trapped magnetic flux
PT and the generated heat Q during pulse field magnetizing(PFM) have been investigated. Important experimental results
and conclusions obtained in this study are summarized asfollows.
FC(1) The trapped magnetic flux FC
T and the trapped field BT
by the field cooled magnetizing (FCM) for the three bulk
discs with the same size are the largest for the GdBaCuO
bulk (Gd bulk) and the smallest for the YBaCuO bulkFC(Y bulk) below 80 K. FC
T and BT correspond to the
maximum ability for the flux trapping in each bulk
superconductor. These results suggest that the pinning
force Fp and the critical current density Jc are the largest
for the Gd bulk and the smallest for the Y bulk. The
SmBaCuO bulk (Sm bulk) has the intermediate ability forthe flux trap among these three bulk superconductors.
(2) For the low pulse field application (Bex = 3.01 T), themagnetic flux uniformly and easily intrudes into the Y bulk
due to the lower Fp compared with the other two bulks.
As a result, the temperature rise of the Y bulk takes place
uniformly in the peripheral region of the bulk disc. On
the other hand, for the Gd and Sm bulk discs with thestronger pinning ability, the surface barrier against the flux
intrusion is partially destroyed at P2 and P3 for the Sm bulk
and only at P1 for the Gd bulk, where the Fp value may belocally weaker and the larger temperature rise takes place.
(3) For the higher pulse field application (Bex  3.87 T), thepinning potential is widely destroyed in the surface regionof all the three bulks and the temperature rise occurs almost
uniformly due to the uniform intrusion of the flux.
(4) The temperature dependence of the specific heatC(T )(=κ/α) of each bulk has been estimated by thesimultaneously measured thermal conductivity κ and theGenerated heat during PFM for REBaCuO (RE = Gd, Sm, Y) bulks

thermal diffusivity α. The C(T ) values of the three bulks
are nearly the same and almost independent of the RE
element and the small difference of the Ag contents.
(5) The generated heat Q during PFM has been estimatedusing the C(T ) value and the maximum temperaturerise Tmax . The Q = Q(No 1)–Q(No 5) value, thedifference between the generated heat of the No 1 pulse
and pulse No 5, is the smallest for the Y bulk. The Qshows a similar Bex dependence as that of the trappedmagnetic flux PT . These results suggest that the Qvalue stands for the heat generation, directly connected to
the flux trapping for pulse No 1.
(6) The Q(No 5) value, which is regarded as the sum of
the pinning hysteresis loss Q sp uncorrelated with the flux
trapping and the viscous flow loss Q v , is the smallest
for the Gd bulk with the strongest Fp . The stronger
pinning force may impede the flow of the untrapped fluxes,
reducing the viscous flow loss.

Acknowledgments
The valuable suggestions by Professor M Ikebe of Iwate
University are gratefully acknowledged. This work is partially
supported by the Japan Science and Technology Agency
under the Joint Research Project for Regional Intensive in the
Iwate Prefecture on development of practical applications ofmagnetic field technology for use in the region and in everyday
living.

References[1] Murakami M, Sakai N, Higuchi T and Yoo S I 1996
Supercond. Sci. Technol. 9 1015
[2] Nariki S, Sakai N and Murakami M 2002 Supercond. Sci.
Technol. 15 235[3] Muralidhar M, Koblischka M R and Murakami M 2001
Supercond. Sci. Technol. 14 1349
[4] Oka T, Yokoyama K and Noto K 2004 IEEE Appl. Supercond.
14 1058[5] Sawamura M and Morita M 2002 Supercond. Sci. Technol. 15
774[6] Tomita M and Murakami M 2003 Nature 421 517[7] Mizutani U, Oka T, Itoh Y, Yanagi Y, Yoshikawa M and
Ikuta H 1998 Appl. Supercond. 6 235[8] Ikuta H, Yanagi Y, Yoshikawa M, Itoh Y, Oka T and
Mizutani U 2001 Physica C 357–360 837[9] Ishihara H, Ikuta H, Itoh Y, Yanagi Y, Yoshikawa M,
Oka T and Mizutani U 2001 Physica C 357–360 763[10] Fujishiro H, Oka T, Yokoyama K and Noto K 2003 Supercond.
Sci. Technol. 16 809[11] Fujishiro H, Oka T, Yokoyama K and Noto K 2004 Supercond.
Sci. Technol. 17 57[12] Fujishiro H, Oka T, Yokoyama K, Kaneyama M andNoto K 2004 IEEE Appl. Supercond. 14 1054
[13] Fujishiro H, Yokoyama K, Kaneyama M, Oka T and
Noto K 2004 Physica C 412–414 646[14] Oka T, Yokoyama K, Kaneyama M, Fujishiro H and
Noto K 2004 Physica C submitted[15] Ikebe M, Fujishiro H, Naito T and Noto K 1994 J. Phys. Soc.
Japan 63 3107
[16] Fujishiro H and Kohayashi S 2002 IEEE Trans. Appl.
Supercond. 12 1124

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