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Magnetic field-direction dependence of critical current density in c-axis oriented Bi2Sr1.7La0.3CuO6+y films
PflYSICA
Physica B 194-196 (1994) 1835-1836 North-Holland
Magnetic field-direction dependence of critical current density in c-axis oriented Bi2Srl.7La0.3CuO6+y films Takeshi Fukami a, Dian-hong Leea , Christos Panagopoulos a, Terukazu Nishizaki a, Fusao Ichikawa a, Yuuji Horie b and Takafumi Aominea a Department of Physics, Kyushu University, Fukuoka 812, Japan b Department of Electrical and Electronics Engineering, Kagoshima University, Kagoshima 890, Japan The magnetic field-direction dependence of the critical current density is studied for the copper oxide superconducting Bi2Sr2_xLaxCuO6+y films prepared by the laser ablation technique. Experimental results are discussed on the basis of the two dimensional properties of magnetic flux lines.
1. I N T R O D U C T I O N Since Kijima et al. observed the superconductivity in B i 2 S r l . 5 L a 0 . 2 C u 2 0 6 + y b u l k samples [1], the physical properties of the Bi2Sr 1_ xLaxCu206+y (BSLC) system have been studied for bulk samples. This compound had a maximum critical temperature of 24 K around.~'=0.4. In order to examine the anisotropic electric properties in the magnetic field H, we measured the field direction dependence of the critical current density Jc(T,H) for films with the preferred c-axis orientation. From the analysis of these data, we discuss the two dimensional properties of flux lines.
10 °
vo
I
10-1
H
,Bo~
°- 2
I
I
°
(X)
AO
o q5=10 ° • q~ = 4 5 ° • ~ :90 °
1 0 -3 0
t
t
O.2
t
I
I
0.4
I
0.6
I
0.8
Hper (m) Figure 1. Jc vs. Hper at T----4.2K. The inlet shows the Jc vs. H as a function of 9 at 4.2 K. whereas the component of H along the basal plane, Hpar, does not affect Jc(4.2 K J-/). In Fig. 2 we plot Jc vs. 9- Experimental results are represented by closed triangles for H=0.1 T and closed circles for 0.4 T. To examine the angular dependence, as a first step let us consider it using the intrinsic pinning model (T-T model) [2]. According to this model, Jc (q) (-= Jc(4.2 K,H, q)) under the condition o f J A_H is represented by
Jc(9)/Jc(O°)=[Jc(90°)/Jc(O°)]/Isinep[1/2,
(1)
where Jc(O °) and Jc(90 °) are the critical current densities in magnetic fields applied along the basal
0921-4526/94/$07.00 © 1994 - Elsevier Science B.V. All rights reserved S S D ! 0921-4526(93)1549-2
I
I
10~
".~:~o
RESULTS
T h e B S L C ( x = 0 . 3 ) f i l m was d e p o s i t e d by the l a s e r a b l a t i o n t e c h n i q u e u s i n g an Ar-F e x c i m e r p u l s e l a s e r on a s i n g l e crystalline MgO (100) substrate. C r y s t a l l i t e s in the f i l m o r i e n t e d t h e i r caxes a l m o s t p e r p e n d i c u l a r l y to the surface o f the s u b s t r a t e . T h e angles q and 0 o f H are m e a s u r e d f r o m the basal p l a n e in the p l a n e p e r p e n d i c u l a r to the c u r r e n t d e n s i t y J and in the p l a n e c o m p r i s i n g b o t h H and J , r e s p e c t i v e l y . T h e c r i t i c a l current was d e t e r m i n e d as the c u r r e n t at which the s a m p l e v o l t a g e r e a c h e d 1 ~uV. Figure 1 shows Jc(4.2 K,Hper)/Jc(4.2 K,0) vs. Hper for three cases. The inlet of Fig. 1 shows the experimental results ofJc(4.2 K,H) as a function of q. Jc(4.2 K,Hper) for 9 = 10°, 45° and 90 ° can be replotted easily, where/-/per= H sinq. It is clear that Jc(4.2 K,H) is determined only by Hper,
I
1°° °~Io~ °E102 • • =4.5*"%% % ~10' AA'~,o~b
I
2. E X P E R I M E N T A L
I
1836 2
i
I
I
I
I
I
I
I
H=-0.1T
•
~:~
H=-0.4T
•
0
0.8,
•
--- 0 . 6 -
I
I
I
I
[
I
I
I
,r <
I 0
E
~,,,~~
% o•
o
o.
o
i
c °
o•
I
I
H=0.2T
@
200
- .
0.2
T=4.2 K
o o
.......
•
"(3-
i
100
l i i-'-t'-r"-r--9 30 60 90 ¢ (deg)
0
o
¢
:3 OC •
o •
plane and the c-axis, respectively. The calculated results are shown by a dotted line for H=0.4 T and a broken line for 0.1 T in Fig. 2. The deviation of the data from the theoretical curve is clear in the low angle side for H=0.4 T. On the other hand, Jc is determined only by Hpe r according to the two dimensional model [3]. Namely,
Jc(T,H, ¢p) = Jc//(T,Hper),
•
o
Figure 2. Jc vs. 9 at T--4.2 K for H=0.1 T (closed triangles) and 0.4 T (closed circles).
(2)
where Jc//(T,Hper) can be calculated using the data of Jc(T,H, 90°). The results are shown by open circles for H = 0.4 T and open triangles for 0.1 T. The two-dimensional model fits much better than the T-T model for H=0.4 T. It is not clear for H=0.1 T which model is better. Figure 3 shows J c ( ~ ) and J c ( 0 ) at T=4.2 K in H=0.2 T. It is clear that both angular dependences coincide. This suggests that Jc of BSLC is determined only by Hper and not by Hpar. Thus, BSLC has two-dimensional electric properties like Bi2Sr2CaCu208 (BSCC) [5-7]. 3.
_1
Exp. 2 D M o d e l T - T M o d e l
O
0
I
300
1 -~
..~ 0.4
I
DISCUSSION
When a magnetic field is applied to a direction inclined from the basal plane, the flux lines would penetrate stepwise with components Hper and/-/par [2]. Furthermore, the dissipation would be related only to Hpe r [3] when the decoupling between the CuO2 planes is strong. This property was confirmed f o r B S C C [5-7].This is t r u e a l s o for B S L C . The physical image of flux lines is qualitatively different f r o m that in traditional type II superconductors [4]. We may imagine a structure as suggested by the two dimealsiolml pancake model for a flux line [4] due to strong two-dimensionality. According to this model, the quantized flux lines
0-1
I
0
I
I
I
c°
°•
I
I
30 60 0 , ¢ (deg)
•
-
90
Figure 3. Comparison between Jc vs. 9 and Jc vs. 0 at T=4.2 K for H = 0 . 2 T. formed from/-/per would penetrate the CuO 2 planes in the normal direction, and the Hpar would spread over the non-superconducting layers owing to the decoupling between the CuO 2 planes. Since only Hpe r rules the field dependence of Jc, we may consider that the constant Lorentz force orienting along the basal plane acts to flux lines as long as ~=0. This model would suggest that in BSLC too Hpar is not concerned with the appearance of the voltage in the mixed state. It should be noted that for Y B a 2 C u 3 O T - 6 the two components a r e concerned with the energy dissipation [8]. REFERENCES
1. T. K i j i m a , J. T a n a k a and Y. Bando, Jpn. J. A p p l . P h y s . 27 ( 1 9 8 8 ) L 1 0 3 5 . 2. M. T a c h i k i and S. T a k a h a s h i , S o l i d S t a t e C o m m u n . 7 2 ( 1 9 8 9 ) 1083. 3. P. H. Kes, J. Aarts, V. M. Vinokur and C. J. van der Beek, Phys. Rev Lett. 64 (1990) 1063. 4. J. R. C l e m , P h y s . R e v . B43 ( 1 9 9 1 ) 7873. 5. H. Raffy, S. Labdi, O. Laborde and P. Monceau, Phys. Rev. Lett. 66 (1991) 2515. 6. P. Schmitt, P. Kummeth, L. Schultz and G. Saemann-Ischenko, Phys. Rev. Lett. 67 (1991) 267. 7. T. Fukami, K. Miyoshi, T. Nishizaki, Y. Horie, F. Ichikawa and T. Aomine, Physica C 202 (1992) 167. 8. T. Nishizaki, F. Ichikawa, T. Fukami, T. Aomine, T. Terashima and Y. Band•, Physica C 204 (1993) 305.
Physica B 194-196 (1994) 1835-1836 North-Holland
Magnetic field-direction dependence of critical current density in c-axis oriented Bi2Srl.7La0.3CuO6+y films Takeshi Fukami a, Dian-hong Leea , Christos Panagopoulos a, Terukazu Nishizaki a, Fusao Ichikawa a, Yuuji Horie b and Takafumi Aominea a Department of Physics, Kyushu University, Fukuoka 812, Japan b Department of Electrical and Electronics Engineering, Kagoshima University, Kagoshima 890, Japan The magnetic field-direction dependence of the critical current density is studied for the copper oxide superconducting Bi2Sr2_xLaxCuO6+y films prepared by the laser ablation technique. Experimental results are discussed on the basis of the two dimensional properties of magnetic flux lines.
1. I N T R O D U C T I O N Since Kijima et al. observed the superconductivity in B i 2 S r l . 5 L a 0 . 2 C u 2 0 6 + y b u l k samples [1], the physical properties of the Bi2Sr 1_ xLaxCu206+y (BSLC) system have been studied for bulk samples. This compound had a maximum critical temperature of 24 K around.~'=0.4. In order to examine the anisotropic electric properties in the magnetic field H, we measured the field direction dependence of the critical current density Jc(T,H) for films with the preferred c-axis orientation. From the analysis of these data, we discuss the two dimensional properties of flux lines.
10 °
vo
I
10-1
H
,Bo~
°- 2
I
I
°
(X)
AO
o q5=10 ° • q~ = 4 5 ° • ~ :90 °
1 0 -3 0
t
t
O.2
t
I
I
0.4
I
0.6
I
0.8
Hper (m) Figure 1. Jc vs. Hper at T----4.2K. The inlet shows the Jc vs. H as a function of 9 at 4.2 K. whereas the component of H along the basal plane, Hpar, does not affect Jc(4.2 K J-/). In Fig. 2 we plot Jc vs. 9- Experimental results are represented by closed triangles for H=0.1 T and closed circles for 0.4 T. To examine the angular dependence, as a first step let us consider it using the intrinsic pinning model (T-T model) [2]. According to this model, Jc (q) (-= Jc(4.2 K,H, q)) under the condition o f J A_H is represented by
Jc(9)/Jc(O°)=[Jc(90°)/Jc(O°)]/Isinep[1/2,
(1)
where Jc(O °) and Jc(90 °) are the critical current densities in magnetic fields applied along the basal
0921-4526/94/$07.00 © 1994 - Elsevier Science B.V. All rights reserved S S D ! 0921-4526(93)1549-2
I
I
10~
".~:~o
RESULTS
T h e B S L C ( x = 0 . 3 ) f i l m was d e p o s i t e d by the l a s e r a b l a t i o n t e c h n i q u e u s i n g an Ar-F e x c i m e r p u l s e l a s e r on a s i n g l e crystalline MgO (100) substrate. C r y s t a l l i t e s in the f i l m o r i e n t e d t h e i r caxes a l m o s t p e r p e n d i c u l a r l y to the surface o f the s u b s t r a t e . T h e angles q and 0 o f H are m e a s u r e d f r o m the basal p l a n e in the p l a n e p e r p e n d i c u l a r to the c u r r e n t d e n s i t y J and in the p l a n e c o m p r i s i n g b o t h H and J , r e s p e c t i v e l y . T h e c r i t i c a l current was d e t e r m i n e d as the c u r r e n t at which the s a m p l e v o l t a g e r e a c h e d 1 ~uV. Figure 1 shows Jc(4.2 K,Hper)/Jc(4.2 K,0) vs. Hper for three cases. The inlet of Fig. 1 shows the experimental results ofJc(4.2 K,H) as a function of q. Jc(4.2 K,Hper) for 9 = 10°, 45° and 90 ° can be replotted easily, where/-/per= H sinq. It is clear that Jc(4.2 K,H) is determined only by Hper,
I
1°° °~Io~ °E102 • • =4.5*"%% % ~10' AA'~,o~b
I
2. E X P E R I M E N T A L
I
1836 2
i
I
I
I
I
I
I
I
H=-0.1T
•
~:~
H=-0.4T
•
0
0.8,
•
--- 0 . 6 -
I
I
I
I
[
I
I
I
,r <
I 0
E
~,,,~~
% o•
o
o.
o
i
c °
o•
I
I
H=0.2T
@
200
- .
0.2
T=4.2 K
o o
.......
•
"(3-
i
100
l i i-'-t'-r"-r--9 30 60 90 ¢ (deg)
0
o
¢
:3 OC •
o •
plane and the c-axis, respectively. The calculated results are shown by a dotted line for H=0.4 T and a broken line for 0.1 T in Fig. 2. The deviation of the data from the theoretical curve is clear in the low angle side for H=0.4 T. On the other hand, Jc is determined only by Hpe r according to the two dimensional model [3]. Namely,
Jc(T,H, ¢p) = Jc//(T,Hper),
•
o
Figure 2. Jc vs. 9 at T--4.2 K for H=0.1 T (closed triangles) and 0.4 T (closed circles).
(2)
where Jc//(T,Hper) can be calculated using the data of Jc(T,H, 90°). The results are shown by open circles for H = 0.4 T and open triangles for 0.1 T. The two-dimensional model fits much better than the T-T model for H=0.4 T. It is not clear for H=0.1 T which model is better. Figure 3 shows J c ( ~ ) and J c ( 0 ) at T=4.2 K in H=0.2 T. It is clear that both angular dependences coincide. This suggests that Jc of BSLC is determined only by Hper and not by Hpar. Thus, BSLC has two-dimensional electric properties like Bi2Sr2CaCu208 (BSCC) [5-7]. 3.
_1
Exp. 2 D M o d e l T - T M o d e l
O
0
I
300
1 -~
..~ 0.4
I
DISCUSSION
When a magnetic field is applied to a direction inclined from the basal plane, the flux lines would penetrate stepwise with components Hper and/-/par [2]. Furthermore, the dissipation would be related only to Hpe r [3] when the decoupling between the CuO2 planes is strong. This property was confirmed f o r B S C C [5-7].This is t r u e a l s o for B S L C . The physical image of flux lines is qualitatively different f r o m that in traditional type II superconductors [4]. We may imagine a structure as suggested by the two dimealsiolml pancake model for a flux line [4] due to strong two-dimensionality. According to this model, the quantized flux lines
0-1
I
0
I
I
I
c°
°•
I
I
30 60 0 , ¢ (deg)
•
-
90
Figure 3. Comparison between Jc vs. 9 and Jc vs. 0 at T=4.2 K for H = 0 . 2 T. formed from/-/per would penetrate the CuO 2 planes in the normal direction, and the Hpar would spread over the non-superconducting layers owing to the decoupling between the CuO 2 planes. Since only Hpe r rules the field dependence of Jc, we may consider that the constant Lorentz force orienting along the basal plane acts to flux lines as long as ~=0. This model would suggest that in BSLC too Hpar is not concerned with the appearance of the voltage in the mixed state. It should be noted that for Y B a 2 C u 3 O T - 6 the two components a r e concerned with the energy dissipation [8]. REFERENCES
1. T. K i j i m a , J. T a n a k a and Y. Bando, Jpn. J. A p p l . P h y s . 27 ( 1 9 8 8 ) L 1 0 3 5 . 2. M. T a c h i k i and S. T a k a h a s h i , S o l i d S t a t e C o m m u n . 7 2 ( 1 9 8 9 ) 1083. 3. P. H. Kes, J. Aarts, V. M. Vinokur and C. J. van der Beek, Phys. Rev Lett. 64 (1990) 1063. 4. J. R. C l e m , P h y s . R e v . B43 ( 1 9 9 1 ) 7873. 5. H. Raffy, S. Labdi, O. Laborde and P. Monceau, Phys. Rev. Lett. 66 (1991) 2515. 6. P. Schmitt, P. Kummeth, L. Schultz and G. Saemann-Ischenko, Phys. Rev. Lett. 67 (1991) 267. 7. T. Fukami, K. Miyoshi, T. Nishizaki, Y. Horie, F. Ichikawa and T. Aomine, Physica C 202 (1992) 167. 8. T. Nishizaki, F. Ichikawa, T. Fukami, T. Aomine, T. Terashima and Y. Band•, Physica C 204 (1993) 305.