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Anisotropy of superconducting properties of Bi-Sr-Ca-Cu-O thin films
Physica B 165&166 (1990) 1423-1424 North- Holland
ANISOTROPY OF SUPERCONDUCTING PROPERTIES OF Bi-Sr-Ca-Cu-O THIN FILMS H. RAFFY', S. LABDr, O. LABORDE6+, and P. MONCEAULi • Laboratoire de Physique des Solides, Universite Paris XI, Bat. 510, 91405 Orsay, France. Li Centre de Recherches sur les Tras Basses Temperatures, C.N.R.S., BP 166 X, 38042 Grenoble-Cedex, France. + Service National des Champs Intenses, C.N.R.S., BP 166 X, 38042 Grenoble-Cedex, France. Angular dependence of the magnetoresistance and of the critical current up to 20 tesla in the bismuth 2212 phase shows remarkable anisotropic behavior. Samples are highly c-axis oriented thin films. The field dependence of the critical current is shown to be essentially dominated by the component of the magnetic field perpendicular to the CU02 layers.
Determination of the critical current density, J c, in high Tc superconductors is of crucial interest. The anisotropic behavior of the superconducting properties is only obtained from single-crystalline materials. Although critical currents can be deduced from the irreversibility in magnetization curves, a direct determination of J c requires epitaxial well oriented thin films. We have deposited 1000 Athick films of amorphous Bi-Sr-9a-Cu-0 oxide onto ambient temperature (100) ori-ented single crystal MgO substrates by DC triode sputtering from a single composite oxide target. The films were subsequently annealed in flowing 02-N2 at 810°-815°C for ten minutes to grow the superconducting phase. Details of this procedure were given in previous papers [1,2). X-ray diffraction studies showed that those samples are composed of the 2212 phase. The films were laserpatterned to 12-18 11m wide and 400-1000 11m long strip lines for transport measurements and four electrical leads were attached to silver contact pads. The films show a zero resistance below T = 85 K. The films used in our work are highly textured with copper oxide planes parallel to the substrate as seen in X-ray spectra (see Fig. 3 in ref. 2). The quality of the films is also revealed by angular dependence of the magnetoresistance in the superconducting state. We accurately define the parallel orientation (H II to the layer structure ) by measuring the resistance of the sample at fixed Hand T as a function of the angle 6 between Hand c (6 = 0 corresponds to HJ} Then we determinate the value of H(6) for a given value of the resistance as a function of e. Fig. 1 shows the variation of H normalized to its value at 6 = 0 (perpendicular orientation, H II c) as a fu nction of 6 for R such that 0.1 RN s; R s; 0.6 RN (RN the normal resistance above Td. HIIIH.L is as large as 30 . This strong anisotropy comparable to that measured in single crystals [3,4] indicates the good quality of the samples. 0921-4526/90/$03.50
© 1990 -
r
30
4
HIS)
IT 20
4 f
T=80 K
10
4
4
I
I
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Tt/2
FIGURE 1 Angular variation of [H(6)/H.l) for 0.1 s; R/RN S; O.~ (RN resistance in the normal state above Tc) for a BI 2212 thin film at T = 80 K (Tc = 87 K). The anisotropy HIIIH.L is larger than 30. e is defined in the inset: HII indicates H parallel to the CU02 layers). The critical current of the specimens was measured either by recording the differential resistance dV/dl as a function of the applied dc current or by a direct dc method with a voltage criterion of a few IlV. The variation of J c as a function of H is shown in Fig. 2 &n a log-log plot: a) at 4.2 K : J c for H.L varies as H with a. = 0.45 up to the largest field. The dSviation of this law only appears below 200 Oe. A
Elsevier Science Publishers B.V. (North-Holland)
1424
H. Raffy, S. Labdi, O. Laborde, P. Monceau
FIGURE 2 Log-Log plot of the critical current Jc of a Bi 2212 thin film as a function of the magnetic field H at T = 4.2 K with H.l. and at T = 50 K with three orientations: H.l. to the layers, HII to the layers but .1 or II to the applied current J for 1 ~ H ~ 20 T.
1.Z ~----,------,
H=O.1T • H=1T o
linear plot in this field range shows a strong reduction of Jc between 0 and 200 Oe which is tentatively attributed to isolated flux motion. b) at 50 K : Jc for HI/but with H .1 J or H 1/ J does not show significant differences although the Lorentz force experienced by the vortices is in principle fundamentally different. Moreover it can be noted that JdH.l.) and JdHI/) can be superposed only by a given translation along the horizontal axis. The angular dependence of Jc is more clearly exhibited in Fig. 3 : Jc is plotted as a function of S at 4.2 K for H = 0.1 T and 1 T. Again the strong anisotropy of the Bi compounds is revealed in the Jc values. The full curves in Fig. 3 correspond to the law; JC.l./[lcosSIJ1/2. This variation results directly from that of Jc a (H.l.)-1I2 as shown in Fig. 2 if it is assumed that only the component of H perpendicular to the (a,b) plane determinates the flux motion [5] ; this result is totally general and independent of the origin of the flux motion. The same type of variation of Je(S) has also been proposed in ref. [6). Any misalignment in the parallel configuration will provide a finite component H.l. and consequently the variation of JdHI/) when H is /I or ..l to J would seem to indicate that the Lorentz force is inoperant as shown in Fig. 2 at T = 50 K; however the perpendicular field component yields a Lorentz force acting parallel to the CU02 plane in both curves H liar .1 to J. In conclusion we have grown highly textured thin films of the Bi 2212 phase. Anisotropy in the magnetoresistance shows the good quality of the films. Critical currents are essentially determined by the component of the magnetic field along c (~asy flux motion along the CU02 plane). Full analysIs of the variation of the resistance and of the critical current as a function of H, e and T will be published elsewhere [7]. ACKNOWLEDGEMENTS HR and SL thank A. Vaures for technical assistance in sample preparation and D.Beaupere(Laboratoires de Marcoussis-CR.CGE) for laser patterning. REFERENCES [1]
oL.... o
.............
. lt/z
[2) --l
8(rad.j
It
[3) [4)
FIGURE 3 Angular dependence of the critical current Jc of a Bi 2212 thin film at T = 4.2 K for H '7t 0.1 and 1 T. The curves are Jc(H.l.)/lcosSI1/2. S = 2" corresponds to HI/, i.e. H parallel to thA Cu02 layers.
[5) [6)
[7J
H. Raffy, A. Vaures, J. Arabski, S. Megtert, F. Rochet, J. Perriere, Solid State Commun. 68 (1988) 235. H. Raffy, S. Labdi, A. Vaures, J. Arabski, S. Megtert, Physica C 162-164 (1989) 613. O. Laborde, P. Manceau, M. Potel, P. Gougeon, J. Padiou, J.C. Levet and H. Noel, Solid State Commun. 67 (1988) 609. M.J. Naughton, R.C. Yu, P.K. Davies, J.E. Fischer, RV. Chamberlin, Z.Z. Wang, TW. Jing, N.P. Ong and P.M. Chaikin, Phys. Rev. B 38 (1988) 9280. P.H. Kes, J. Aarts, V.M. Vinokur and C.J. van der Beck, Phys. Rev. Lett. 64 (1990) 1063. M. Tachiki and S. Takahashi, Solid State Commun. 72 (1989) 1083. H. Raffy et al., to be published.
ANISOTROPY OF SUPERCONDUCTING PROPERTIES OF Bi-Sr-Ca-Cu-O THIN FILMS H. RAFFY', S. LABDr, O. LABORDE6+, and P. MONCEAULi • Laboratoire de Physique des Solides, Universite Paris XI, Bat. 510, 91405 Orsay, France. Li Centre de Recherches sur les Tras Basses Temperatures, C.N.R.S., BP 166 X, 38042 Grenoble-Cedex, France. + Service National des Champs Intenses, C.N.R.S., BP 166 X, 38042 Grenoble-Cedex, France. Angular dependence of the magnetoresistance and of the critical current up to 20 tesla in the bismuth 2212 phase shows remarkable anisotropic behavior. Samples are highly c-axis oriented thin films. The field dependence of the critical current is shown to be essentially dominated by the component of the magnetic field perpendicular to the CU02 layers.
Determination of the critical current density, J c, in high Tc superconductors is of crucial interest. The anisotropic behavior of the superconducting properties is only obtained from single-crystalline materials. Although critical currents can be deduced from the irreversibility in magnetization curves, a direct determination of J c requires epitaxial well oriented thin films. We have deposited 1000 Athick films of amorphous Bi-Sr-9a-Cu-0 oxide onto ambient temperature (100) ori-ented single crystal MgO substrates by DC triode sputtering from a single composite oxide target. The films were subsequently annealed in flowing 02-N2 at 810°-815°C for ten minutes to grow the superconducting phase. Details of this procedure were given in previous papers [1,2). X-ray diffraction studies showed that those samples are composed of the 2212 phase. The films were laserpatterned to 12-18 11m wide and 400-1000 11m long strip lines for transport measurements and four electrical leads were attached to silver contact pads. The films show a zero resistance below T = 85 K. The films used in our work are highly textured with copper oxide planes parallel to the substrate as seen in X-ray spectra (see Fig. 3 in ref. 2). The quality of the films is also revealed by angular dependence of the magnetoresistance in the superconducting state. We accurately define the parallel orientation (H II to the layer structure ) by measuring the resistance of the sample at fixed Hand T as a function of the angle 6 between Hand c (6 = 0 corresponds to HJ} Then we determinate the value of H(6) for a given value of the resistance as a function of e. Fig. 1 shows the variation of H normalized to its value at 6 = 0 (perpendicular orientation, H II c) as a fu nction of 6 for R such that 0.1 RN s; R s; 0.6 RN (RN the normal resistance above Td. HIIIH.L is as large as 30 . This strong anisotropy comparable to that measured in single crystals [3,4] indicates the good quality of the samples. 0921-4526/90/$03.50
© 1990 -
r
30
4
HIS)
IT 20
4 f
T=80 K
10
4
4
I
I
4 4' 4 _ _ 4_4_4-
o
""If-
oA'>
e(rad.)
Tt/2
FIGURE 1 Angular variation of [H(6)/H.l) for 0.1 s; R/RN S; O.~ (RN resistance in the normal state above Tc) for a BI 2212 thin film at T = 80 K (Tc = 87 K). The anisotropy HIIIH.L is larger than 30. e is defined in the inset: HII indicates H parallel to the CU02 layers). The critical current of the specimens was measured either by recording the differential resistance dV/dl as a function of the applied dc current or by a direct dc method with a voltage criterion of a few IlV. The variation of J c as a function of H is shown in Fig. 2 &n a log-log plot: a) at 4.2 K : J c for H.L varies as H with a. = 0.45 up to the largest field. The dSviation of this law only appears below 200 Oe. A
Elsevier Science Publishers B.V. (North-Holland)
1424
H. Raffy, S. Labdi, O. Laborde, P. Monceau
FIGURE 2 Log-Log plot of the critical current Jc of a Bi 2212 thin film as a function of the magnetic field H at T = 4.2 K with H.l. and at T = 50 K with three orientations: H.l. to the layers, HII to the layers but .1 or II to the applied current J for 1 ~ H ~ 20 T.
1.Z ~----,------,
H=O.1T • H=1T o
linear plot in this field range shows a strong reduction of Jc between 0 and 200 Oe which is tentatively attributed to isolated flux motion. b) at 50 K : Jc for HI/but with H .1 J or H 1/ J does not show significant differences although the Lorentz force experienced by the vortices is in principle fundamentally different. Moreover it can be noted that JdH.l.) and JdHI/) can be superposed only by a given translation along the horizontal axis. The angular dependence of Jc is more clearly exhibited in Fig. 3 : Jc is plotted as a function of S at 4.2 K for H = 0.1 T and 1 T. Again the strong anisotropy of the Bi compounds is revealed in the Jc values. The full curves in Fig. 3 correspond to the law; JC.l./[lcosSIJ1/2. This variation results directly from that of Jc a (H.l.)-1I2 as shown in Fig. 2 if it is assumed that only the component of H perpendicular to the (a,b) plane determinates the flux motion [5] ; this result is totally general and independent of the origin of the flux motion. The same type of variation of Je(S) has also been proposed in ref. [6). Any misalignment in the parallel configuration will provide a finite component H.l. and consequently the variation of JdHI/) when H is /I or ..l to J would seem to indicate that the Lorentz force is inoperant as shown in Fig. 2 at T = 50 K; however the perpendicular field component yields a Lorentz force acting parallel to the CU02 plane in both curves H liar .1 to J. In conclusion we have grown highly textured thin films of the Bi 2212 phase. Anisotropy in the magnetoresistance shows the good quality of the films. Critical currents are essentially determined by the component of the magnetic field along c (~asy flux motion along the CU02 plane). Full analysIs of the variation of the resistance and of the critical current as a function of H, e and T will be published elsewhere [7]. ACKNOWLEDGEMENTS HR and SL thank A. Vaures for technical assistance in sample preparation and D.Beaupere(Laboratoires de Marcoussis-CR.CGE) for laser patterning. REFERENCES [1]
oL.... o
.............
. lt/z
[2) --l
8(rad.j
It
[3) [4)
FIGURE 3 Angular dependence of the critical current Jc of a Bi 2212 thin film at T = 4.2 K for H '7t 0.1 and 1 T. The curves are Jc(H.l.)/lcosSI1/2. S = 2" corresponds to HI/, i.e. H parallel to thA Cu02 layers.
[5) [6)
[7J
H. Raffy, A. Vaures, J. Arabski, S. Megtert, F. Rochet, J. Perriere, Solid State Commun. 68 (1988) 235. H. Raffy, S. Labdi, A. Vaures, J. Arabski, S. Megtert, Physica C 162-164 (1989) 613. O. Laborde, P. Manceau, M. Potel, P. Gougeon, J. Padiou, J.C. Levet and H. Noel, Solid State Commun. 67 (1988) 609. M.J. Naughton, R.C. Yu, P.K. Davies, J.E. Fischer, RV. Chamberlin, Z.Z. Wang, TW. Jing, N.P. Ong and P.M. Chaikin, Phys. Rev. B 38 (1988) 9280. P.H. Kes, J. Aarts, V.M. Vinokur and C.J. van der Beck, Phys. Rev. Lett. 64 (1990) 1063. M. Tachiki and S. Takahashi, Solid State Commun. 72 (1989) 1083. H. Raffy et al., to be published.