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Anisotropy and anomalous temperature dependence of Josephson lower critical field in grain-oriented Bi-Pb-Sr-Ca-Cu-O superconductor
PhysicaC 177 (1991) North-Holland
135-137
Anisotropy and anomalous temperature dependence of Josephson lower critical field in grain-oriented Bi-Pb-Sr-Ca-Cu-0 superconductor Norimitsu
Murayama,
Yasuharu
Kodama,
Shuji Sakaguchi
and Fumihiro
Wakai
Government Industrial Research Institute, Nagoya, l-l Hirate-cho, Kita-ku, Nagoya 462, Japan Received
29 March
199 1
A dense and grain-oriented Bi0.85Pb0.,5Sr0.8CaCu,.40v superconductor was prepared by hot-pressing. The lower critical field lower critical field (H,,,) due to the weak link between grains were measured from initial magnetization curves. Anisotropy in H,,, was observed below 77 K. The value of H,,, and H,, rapidly increased below 20 and 40 K, respectively.
(H,, ) and Josephson
1. Introduction Recently, it has been reported that the lower critical field H,, rapidly increases when the temperature is lower than a certain value in several oxide superconductors [ l-8 1. Koyama et al. [ 9 ] have presented a theory in which this anomalous temperature dependence of I-r,, comes from the intrinsic property of a flux line in the multilayer structure of the oxide superconductors which consist of the superconducting layer (i.e., Cu02 plane) and the normal layers such as St-0 and CaO. At higher temperatures the superconducting order in the normal layers is strongly suppressed and the superconduction state is maintained mainly by the superconducting layers. At lower temperatures the superconducting order in the normal layers is induced by a proximity effect, so that the order extends over both superconducting and normal layers resulting in a strong enhancement of H,, . The anomalous temperature dependence of H,, arises from the crossover between the two temperature regimes. In granular superconductors, flux starts to enter into the sample through the grain boundary at the Josephson lower critical field H,,, which is lower than H,,, because of the Josephson weak link between grains [ 10,111. An anomalous temperature dependence of H,,,, the same as that of H,,, is predicted. In this study, anisotropy in transport properties and 0921-4534/91/$03.50 0 1991 - Elsevier Science Publishers
H,,, is investigated in a grain-oriented Bi-Pb-Sr-CaCu-0 superconductor which is prepared by hotpressing, and the temperature dependence of H,,, is compared with that of H,,.
2. Experimental A dense Bio.ssPbo.I 5Sr,&aCu,.40y granular superconductor was prepared by hot-pressing. The detail of the sample preparation is described elsewhere [ 121. The hot-pressed block was 27 mm in diameter and 10 mm in height. X-ray diffraction (XRD) data were taken for the hot-pressed sample at room temperature with graphite-monochromatized Cu radiation. The hot-pressed block was cut into 0.5 mm X 0.5 mm x 10 mm bars for transport properties measurement. The values of T, and J, along the direction perpendicular and parallel to the hot-pressing direction were measured by a four-probe DC method. The J, measurement was carried out in liquid nitrogen and in zero magnetic field. The J, was calculated by dividing the critical current by the cross-sectional area of the sample. The size of the sample for magnetic properties measurement was 3 mm X 3 mm X 1 mm. The hot-pressed block was cut so that the basal plane of the sample was parallel to the hot-pressing direction. The initial magnetization curve was measured for the powder and the sintered body at a temper-
B.V. (North-Holland)
136
N. Murayama
et al. /Properties
ature range of 5 to 77 K. The magnetic field was always applied parallel to the basal plane of the sample and was applied perpendicularly and parallel to the hot-pressing direction for one sample. The values of H,, and H,,, were defined as the field at which the magnetization curve first deviates from linearity for the powder and the sintered body, respectively.
ofgrain-oriented
Bi-Pb-Sr-Ca-Cu-0
Table 1 Anisotropy in transport properties Bi0.8sPbo,,SrosCaCu,.40, superconductor
current I hot-pressing current /( hot-pressing
for
the
hot-pressed
pat 130K (lo-3Rcm)
T, (K)
J,at77K,OOe
0.96
102
375
2.8
101
267
(A/cm’)
direction direction
3. Results and discussion Figure 1 shows XRD patterns for the perpendicular plane (a), and the parallel plane (b) to the hotpressing direction of the hot-pressed sample. The grains were found to be oriented with the c-axis along the hot-pressing direction. The degree of grain orientation was lower than that of the hot-pressed sample prepared in the previous work [ 131. This was due to the reduced effect of mechanical stress on the grain orientation because the present sample is thicker in the direction of the hot-pressing axis. Table 1 shows T,, J, and resistivity at room temperature. Subscripts I and 1)represent transport current direction perpendicular and parallel to the hot-pressing direction, respectively. The anisotropy in these properties was observed, which was not so large as compared
2 ‘5 .-
0.5-
H=lOOOOe
5 m ii O-
80
100 Temperature
120 (K
)
>1 C .? z ,
(a) I HP 0
x
d 2
z
I clz 0 8 80
100 Temperature
120 (K)
L”
Fig. 2. Temperature dependence of resistivity at 0 and 1000 Oe for the hot-pressed sample. Transport current flows (a) perpendicular and (b) parallel to the hot-pressing direction.
B
(b) //HP
2..
g=
8 0
x
s J 5
10
20 30 40 50 28 (degree) Fig. 1. X-ray diffraction patterns for the perpendicular (a), and the parallel (b) planes to the pressing direction of the hot-pressed Bi-Pb-Sr-Ca-Cu-0 superconductor.
with that of a single crystal 3 141. It is due to the low degree of grain orientation of the sample. Figure 2 shows the temperature dependence of the resistivity. When a magnetic field was applied, the tailing phenomenon was observed, which was due to the weak link between grains. When the transport current flowed perpendicularly to the hot-pressing direction, T, was independent of the angle between the transport current and magnetic field direction. This result
N. Murayama et al. /Properties ofgrain-oriented Bi-Pb-Sr-Ca-Cu-0
indicates that the decrease in T, due to the magnetic field is not governed by flux depinning. The decrease in T, in the case of H 1)hot-pressing direction was larger than that in the case of HI hot-pressing direction, regardless of the transport current direction. Figure 3 shows the temperature dependence of H,, and H,,,. The H,,, in the magnetic field perpendicular and parallel to the hot-pressing direction were indicated by H,,, I and HcIJ,,, respectively. The value of H,, rapidly increased at the temperature range lower than about 40 K. This result was similar to that in Job et al.‘s work [ 8 1. The value of H,,, I and HclJ,, were almost the same at 77 K and the anisotropy in H,,, was observed at lower temperatures. The value
137
Of &J
rapidly increased at the temperature range lower than about 20 K. This temperature was lower than that for H,,. The reason seems to be that the thickness of the Josephson junction between grains is longer than the distance between the Cu02 layers.
4. Conclusion It was found that H,,J due to the weak link between grains rapidly increased below 20 K as well granular superas H,r in a Bi-Pb-Sr-Ca-Cu-0 conductor.
References [1 J.P. Strobel,
3oc
8 -J 200 4 4
100
,-
CI-
O
I
20
h
I
40
60
80
I
Temp.lKl Fig. 3. Temperature dependence of H,, and H,,,. The H,,,‘s in a magnetic field perpendicular and parallel to the hot-pressing direction are indicated by HclJl and Hcl,,,, respectively.
A. Thoma, B. Hensel, H. Adrian and G. Saeman-Ischenco, Physica C 153-l 55 (1988) 1537. L-2 N. Kobayashi, H. Iwasaki, S. Terada, K. Noto, A. Tokiwa, M. Kikuchi, Y. Shono and Y. Muto, Physica C 153-l 55 (1988) 1525. H. Adrian, W. Assmus, A. Horh, J. Koalewski, H. Spille and F. Steghch, Physica C 162-l 64 ( 1989) 329. A. Umezawa, G.W. Crabtree, K.G. Vandervoort, U. Welp, W.K. Kwok and J.Z. Liu, Physica C 162-164 (1989) 733. ‘I V.N. Kopylov and I.F. Schegolev, Physica C 162-164 (1989) 1143. M. Wacenovsky, H.W. Weber, O.B. Hyun and D.K. Finnemore, Physica C 162-164 ( 1989) 1629. [ 71 M. Sato. S. Shamato, M. Sera and H. Fujishima, Solid State Commun. 72 (1989) 689. [ 8 ] R. Job and M. Rosenberg, Physica C 172( 1991) 391. [9] T. Koyama, N. Takezawa and M. Tachiki, Physica C 168 ( 1990) 69. [IO] K.-H. Muller, J.C. Macfarlane and R. Driver, Physica C 158 (1989) 69. [ 111P.P. Durand and L.H. Ungar, Phys. Rev. B 41 ( 1990) 815. [ 121 N. Murayama, Y. Kodama, F. Wakai, S. Sakaguchi and Y. Torii, Jpn. J. Appl. Phys. 28 ( 1989) L1740. [ 131 N. Murayama, E. Sudo, M. Awano, K. Kani and Y. Torii, Jpn. J. Appt. Phys. 27 (1988) L1856. [ 141 S. Nomura, Y. Yamada, T. Yamashita and H. Yoshino, J. Appl. Phys. 67 ( 1990) 547.
135-137
Anisotropy and anomalous temperature dependence of Josephson lower critical field in grain-oriented Bi-Pb-Sr-Ca-Cu-0 superconductor Norimitsu
Murayama,
Yasuharu
Kodama,
Shuji Sakaguchi
and Fumihiro
Wakai
Government Industrial Research Institute, Nagoya, l-l Hirate-cho, Kita-ku, Nagoya 462, Japan Received
29 March
199 1
A dense and grain-oriented Bi0.85Pb0.,5Sr0.8CaCu,.40v superconductor was prepared by hot-pressing. The lower critical field lower critical field (H,,,) due to the weak link between grains were measured from initial magnetization curves. Anisotropy in H,,, was observed below 77 K. The value of H,,, and H,, rapidly increased below 20 and 40 K, respectively.
(H,, ) and Josephson
1. Introduction Recently, it has been reported that the lower critical field H,, rapidly increases when the temperature is lower than a certain value in several oxide superconductors [ l-8 1. Koyama et al. [ 9 ] have presented a theory in which this anomalous temperature dependence of I-r,, comes from the intrinsic property of a flux line in the multilayer structure of the oxide superconductors which consist of the superconducting layer (i.e., Cu02 plane) and the normal layers such as St-0 and CaO. At higher temperatures the superconducting order in the normal layers is strongly suppressed and the superconduction state is maintained mainly by the superconducting layers. At lower temperatures the superconducting order in the normal layers is induced by a proximity effect, so that the order extends over both superconducting and normal layers resulting in a strong enhancement of H,, . The anomalous temperature dependence of H,, arises from the crossover between the two temperature regimes. In granular superconductors, flux starts to enter into the sample through the grain boundary at the Josephson lower critical field H,,, which is lower than H,,, because of the Josephson weak link between grains [ 10,111. An anomalous temperature dependence of H,,,, the same as that of H,,, is predicted. In this study, anisotropy in transport properties and 0921-4534/91/$03.50 0 1991 - Elsevier Science Publishers
H,,, is investigated in a grain-oriented Bi-Pb-Sr-CaCu-0 superconductor which is prepared by hotpressing, and the temperature dependence of H,,, is compared with that of H,,.
2. Experimental A dense Bio.ssPbo.I 5Sr,&aCu,.40y granular superconductor was prepared by hot-pressing. The detail of the sample preparation is described elsewhere [ 121. The hot-pressed block was 27 mm in diameter and 10 mm in height. X-ray diffraction (XRD) data were taken for the hot-pressed sample at room temperature with graphite-monochromatized Cu radiation. The hot-pressed block was cut into 0.5 mm X 0.5 mm x 10 mm bars for transport properties measurement. The values of T, and J, along the direction perpendicular and parallel to the hot-pressing direction were measured by a four-probe DC method. The J, measurement was carried out in liquid nitrogen and in zero magnetic field. The J, was calculated by dividing the critical current by the cross-sectional area of the sample. The size of the sample for magnetic properties measurement was 3 mm X 3 mm X 1 mm. The hot-pressed block was cut so that the basal plane of the sample was parallel to the hot-pressing direction. The initial magnetization curve was measured for the powder and the sintered body at a temper-
B.V. (North-Holland)
136
N. Murayama
et al. /Properties
ature range of 5 to 77 K. The magnetic field was always applied parallel to the basal plane of the sample and was applied perpendicularly and parallel to the hot-pressing direction for one sample. The values of H,, and H,,, were defined as the field at which the magnetization curve first deviates from linearity for the powder and the sintered body, respectively.
ofgrain-oriented
Bi-Pb-Sr-Ca-Cu-0
Table 1 Anisotropy in transport properties Bi0.8sPbo,,SrosCaCu,.40, superconductor
current I hot-pressing current /( hot-pressing
for
the
hot-pressed
pat 130K (lo-3Rcm)
T, (K)
J,at77K,OOe
0.96
102
375
2.8
101
267
(A/cm’)
direction direction
3. Results and discussion Figure 1 shows XRD patterns for the perpendicular plane (a), and the parallel plane (b) to the hotpressing direction of the hot-pressed sample. The grains were found to be oriented with the c-axis along the hot-pressing direction. The degree of grain orientation was lower than that of the hot-pressed sample prepared in the previous work [ 131. This was due to the reduced effect of mechanical stress on the grain orientation because the present sample is thicker in the direction of the hot-pressing axis. Table 1 shows T,, J, and resistivity at room temperature. Subscripts I and 1)represent transport current direction perpendicular and parallel to the hot-pressing direction, respectively. The anisotropy in these properties was observed, which was not so large as compared
2 ‘5 .-
0.5-
H=lOOOOe
5 m ii O-
80
100 Temperature
120 (K
)
>1 C .? z ,
(a) I HP 0
x
d 2
z
I clz 0 8 80
100 Temperature
120 (K)
L”
Fig. 2. Temperature dependence of resistivity at 0 and 1000 Oe for the hot-pressed sample. Transport current flows (a) perpendicular and (b) parallel to the hot-pressing direction.
B
(b) //HP
2..
g=
8 0
x
s J 5
10
20 30 40 50 28 (degree) Fig. 1. X-ray diffraction patterns for the perpendicular (a), and the parallel (b) planes to the pressing direction of the hot-pressed Bi-Pb-Sr-Ca-Cu-0 superconductor.
with that of a single crystal 3 141. It is due to the low degree of grain orientation of the sample. Figure 2 shows the temperature dependence of the resistivity. When a magnetic field was applied, the tailing phenomenon was observed, which was due to the weak link between grains. When the transport current flowed perpendicularly to the hot-pressing direction, T, was independent of the angle between the transport current and magnetic field direction. This result
N. Murayama et al. /Properties ofgrain-oriented Bi-Pb-Sr-Ca-Cu-0
indicates that the decrease in T, due to the magnetic field is not governed by flux depinning. The decrease in T, in the case of H 1)hot-pressing direction was larger than that in the case of HI hot-pressing direction, regardless of the transport current direction. Figure 3 shows the temperature dependence of H,, and H,,,. The H,,, in the magnetic field perpendicular and parallel to the hot-pressing direction were indicated by H,,, I and HcIJ,,, respectively. The value of H,, rapidly increased at the temperature range lower than about 40 K. This result was similar to that in Job et al.‘s work [ 8 1. The value of H,,, I and HclJ,, were almost the same at 77 K and the anisotropy in H,,, was observed at lower temperatures. The value
137
Of &J
rapidly increased at the temperature range lower than about 20 K. This temperature was lower than that for H,,. The reason seems to be that the thickness of the Josephson junction between grains is longer than the distance between the Cu02 layers.
4. Conclusion It was found that H,,J due to the weak link between grains rapidly increased below 20 K as well granular superas H,r in a Bi-Pb-Sr-Ca-Cu-0 conductor.
References [1 J.P. Strobel,
3oc
8 -J 200 4 4
100
,-
CI-
O
I
20
h
I
40
60
80
I
Temp.lKl Fig. 3. Temperature dependence of H,, and H,,,. The H,,,‘s in a magnetic field perpendicular and parallel to the hot-pressing direction are indicated by HclJl and Hcl,,,, respectively.
A. Thoma, B. Hensel, H. Adrian and G. Saeman-Ischenco, Physica C 153-l 55 (1988) 1537. L-2 N. Kobayashi, H. Iwasaki, S. Terada, K. Noto, A. Tokiwa, M. Kikuchi, Y. Shono and Y. Muto, Physica C 153-l 55 (1988) 1525. H. Adrian, W. Assmus, A. Horh, J. Koalewski, H. Spille and F. Steghch, Physica C 162-l 64 ( 1989) 329. A. Umezawa, G.W. Crabtree, K.G. Vandervoort, U. Welp, W.K. Kwok and J.Z. Liu, Physica C 162-164 (1989) 733. ‘I V.N. Kopylov and I.F. Schegolev, Physica C 162-164 (1989) 1143. M. Wacenovsky, H.W. Weber, O.B. Hyun and D.K. Finnemore, Physica C 162-164 ( 1989) 1629. [ 71 M. Sato. S. Shamato, M. Sera and H. Fujishima, Solid State Commun. 72 (1989) 689. [ 8 ] R. Job and M. Rosenberg, Physica C 172( 1991) 391. [9] T. Koyama, N. Takezawa and M. Tachiki, Physica C 168 ( 1990) 69. [IO] K.-H. Muller, J.C. Macfarlane and R. Driver, Physica C 158 (1989) 69. [ 111P.P. Durand and L.H. Ungar, Phys. Rev. B 41 ( 1990) 815. [ 121 N. Murayama, Y. Kodama, F. Wakai, S. Sakaguchi and Y. Torii, Jpn. J. Appl. Phys. 28 ( 1989) L1740. [ 131 N. Murayama, E. Sudo, M. Awano, K. Kani and Y. Torii, Jpn. J. Appt. Phys. 27 (1988) L1856. [ 141 S. Nomura, Y. Yamada, T. Yamashita and H. Yoshino, J. Appl. Phys. 67 ( 1990) 547.