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Transverse a.c. susceptibility measurements on a textured YBa2Cu3O7−δ sample
PHISICA
Physica C 235-240 (1994)3183-3184 North-Holland
Transverse a.c. susceptibility measurements on a textured YBa2Cu307. ~ sample J. Filippi I , P. Pugnat I , B. Barbara 1, M. Ingold 2, D. Bourgault 3, and R. Tournier 3 1Laboratoire de magn6tisme Louis N6el, CNRS, B.P. 166, 38042 Grenoble, France. 2Merlin Gerin, D6partement des Recherches g6n6rales, rue Henri Tarze, 38050 Grenoble, France. 3 Laboratoire de la 16vitation et de la force magn6tique, CNRS, B.P. 166, 38042 Grenoble, France. The temperature range near T c of a magnetically melt textured YBa2Cu307_ 8 sample (Tc = 90 K) has been studied by a.c. susceptibility measurements (X = X'- ix") in the particular geometry where the static field (H) is applied perpendicularly to the a.c. one. As for longitudinal measurements, the imaginary part X" exhibits a well defined maximum at a temperature T*(H). The interpretation in terms of a (new) irreversible line is proposed. This line displays the same power law H*(T) = a (1-T/Tc)2 for a static field applied parallel and perpendicular to the mean ?-axis direction with different coefficients a. Frequency effects are also evidenced.
The High Temperature Superconductors (H.T.S.) structure consists of a stack of coupled superconducting cells made up of one or more CuO2 planes. One of the key point for the industrial applications of H.T.S. is to preserve at the best such a layered structure in the fabrication of big sample. This can be obtained by appropriate texturization. For example, in the case of Magnetically Melt Textured YBa2Cu3OT_ ~ samples, critical currents higher than 104 A/cm2 in a field of 20 Tesla are obtained [ 1] . . . . . . Our experimental investigation was carried out on such a Magnetically Melt Textured (M.M.T.) YBa2Cu3OT-8 sample with Tc -- 90 K in zero field. The critical currents measured on this sample in a 7 Tesla field at 77 K is of order of 104 A/cm 2 [2]. The approximate size of the parallelepiped shape is 1.5 x 1 x 0.4 m m 3. We report here some transverse a.c. susceptibility measurements i.e. with the static field (H) applied perpendicular to the alternative one (ha.c). Such susceptibility experiments have been extensively used to study the dynamical properties of some random anisotropic ferromagnets [3]. For type II superconductors, the principal difference b e t w e e n t r a n s v e r s e and l o n g i t u d i n a l a.c. experiments can be briefly summarised by the following description. The Flux Line Lattice (F.L.L.) created by the static field interacts with the a.c. induced currents which circulates in a layer of thickness equal to the temperature dependent magnetic penetration depth L(T). For transverse a.c. susceptibility measurements, the response comes from the bending of each vortex which corresponds to the collective tilt mode of the F.L.L. In the case of longitudinal a.c. excitation, it is mainly the compressive mode of the F.L.L. which is concerned
0,05 . . . . . . . . . . . . . . . . . . . h., = Z Oe ~,, r = ls8 Ha ± ~ ~ k. . . . . . . . . . . . . --" 0 ,, tI -~~':. .' : : • o °" ~ 0.06 kOe X' " : *: * ~ -0,05 0.5 kOe ," ." ~:" o* ~ * 1 kOe ,, , o, ~ • 2 kOe j,* ." ~5 J -0 1[ - 4 kOe ,,1//j: .: 'I ---~ ~ ~ ' -0 15 80
84
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.
90 T (K) Fig, 1 : Thermal variations of X' and X" of the transverse a.c. susceptibility for different values of the static field H applied parallely to the mean (~, b ) planes direction of a M. M. T. YBa2Cu3OT~ sample. giving rise also to a collective response (see for example[4]). For all the set of measurements exposed here, ha.c was applied perpendicularly to the mean direction o f the ~-axis (along the sample side o f I mm long) with a constant amplitude of 2 Oe. Only the low frequency range was investigated (f<1000 Hz) and we s h o w first on Fig.1 t y p i c a l measurements of the real Z' and imaginary part Z" of the transverse a.c. susceptibility. Such results were obtained at f = 158 Hz for different values o f the static field H which is applied perpendicularly to the mean direction of the ~-axis (within a few degrees). As for the case o f longitudinal susceptibility measurements, )C" exhibits a well defined maximum at a temperature T*(H) whereas
0921-4534/94/$07.00 © 1994 Elsevier Science B.V. All rights reserved. SSDI 0921-4534(94)02157-0 -
82
3184
,~ Filippi et a L / P h y s i c a C 235-240 (1994) 3183 ~ 3184
Z' varies monotonously. This maximum defines a transverse irreversible line in the Field-Temperature plane. The best fit of this line (Fig.2) is given by the following power law : H*(T) = a//(1-T/Tc) 2 with a//(158Hz) --- 940 Tesla for the static field applied parallely to the mean (~, b) planes direction. The value o f T c ( ~ 89.8 K) has been determined independently from the extrapolation of the temperature dependence of the onset of dissipation as a function of the static field H (Fig.2). This line can be connected with the formation of vortices at the upper critical field Hc2//parallel to the mean (~, b) planes direction. Such an interpretation cannot be done without having in mind that the upper critical field Hc2 characterises the nucleation of superconductivity in an homogeneous bulk. In the case o f M.M.T. YBa2Cu307_ 8 samples other non-superconducting phases are generally present like Y2BaCuO 5 precipitates at a concentration of the order of 20 % [2]. The presence in the bulk of I n s u l a t i n g / S u p e r c o n d u c t i n g interfaces o f size distributed precipitates can reasonably call into question the use of the "homogeneous description". We will not consider this aspect here, the same measurements done in YBa2Cu307_5 crystal giving similar results but with a different power law for the irreversible line [5]. The temperature dependence of an effective Hc2//(T) has been then extracted from the ~" measurements (Fig.2). As we can see, a linear variation of Hc2//(T) is obtain near T c with a slope approximately equal to -0.3 Tesla/Kelvin. This low value can be explained not only by a disorientation o f the static field but also by the microstructure of the textured sample. We now try to discuss briefly about the physical meaning of the parabolic variation of the maximum of Z" shown on Fig.2. As for longitudinal a.c. m e a s u r e m e n t s (see for example [6]), the "reversible" range in the (H,T) diagram is reduced in the two following cases : When the frequency is increased, a//(980Hz) = 1200 Tesla, and when the static field is parallel to the mean direction of the (fi, b) planes, a L(980Hz) --- 825 Tesla. Theses variations o f the temperature dependence of the irreversible line H*(T) are qualitatively similar to those observed in longitudinal a.c. measurements [6]. As in this case, we can then interpret the transverse irreversible lines shown on Fig.2 in the framework of the thermally activated flux-creep model which combines both pinning and flux flow
5
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.
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88.5 89 89.5 90 Y (K) Fig.2 : The solid line represent the linear fit of the variation of the onset of appearance of dissipation for static field applied parallely to the mean direction of (~, b ) planes. The dashed lines show the parabolic fit of variations of the maximum of dissipation for different set of measurements.
of vortices. But for our measurements we must consider a "transverse" critical state defined by the bending of flux line [5]. Acknowledgements
:
The authors would like to thank R. Weber for his help during the experiment and the Region Rh6ne-Alpes for their financial support. References :
[1] D. Braithwaite, D. Bourgault, N. Schopohl, R. Tournier, J.M. Barbut, and J. C. Vallier, J. Low Temp. Phys. 92, (1993), 295. [2] M. R. Lees, D. Bourgault, D. Braithwaite, P. de Rango, P. Lejay, A. Sulpice and R. Tournier, Physica C 191 (1992)414. [3] B. Barbara, B. Dieny and J. Filippi, "Relaxation in Complex Systms and Related Topics", Ed. by !. A. Campbell and C. Giovannella (Plenum Press, New York, 1990) 31. [4] E.H. Brandt, Vortices in Superfluids, NATO Advanced Study Institute, July 19-31 1993, in Carg~se, Corsica. [5] P. Pugnat, J. Filippi and B. Barbara, to be published. [6] A. P. Malozemoff, in "Physical properties of High Temperature Superconductors", Ed. D. Ginsberg (World Scientific, Singapore, 1988) 71.
Physica C 235-240 (1994)3183-3184 North-Holland
Transverse a.c. susceptibility measurements on a textured YBa2Cu307. ~ sample J. Filippi I , P. Pugnat I , B. Barbara 1, M. Ingold 2, D. Bourgault 3, and R. Tournier 3 1Laboratoire de magn6tisme Louis N6el, CNRS, B.P. 166, 38042 Grenoble, France. 2Merlin Gerin, D6partement des Recherches g6n6rales, rue Henri Tarze, 38050 Grenoble, France. 3 Laboratoire de la 16vitation et de la force magn6tique, CNRS, B.P. 166, 38042 Grenoble, France. The temperature range near T c of a magnetically melt textured YBa2Cu307_ 8 sample (Tc = 90 K) has been studied by a.c. susceptibility measurements (X = X'- ix") in the particular geometry where the static field (H) is applied perpendicularly to the a.c. one. As for longitudinal measurements, the imaginary part X" exhibits a well defined maximum at a temperature T*(H). The interpretation in terms of a (new) irreversible line is proposed. This line displays the same power law H*(T) = a (1-T/Tc)2 for a static field applied parallel and perpendicular to the mean ?-axis direction with different coefficients a. Frequency effects are also evidenced.
The High Temperature Superconductors (H.T.S.) structure consists of a stack of coupled superconducting cells made up of one or more CuO2 planes. One of the key point for the industrial applications of H.T.S. is to preserve at the best such a layered structure in the fabrication of big sample. This can be obtained by appropriate texturization. For example, in the case of Magnetically Melt Textured YBa2Cu3OT_ ~ samples, critical currents higher than 104 A/cm2 in a field of 20 Tesla are obtained [ 1] . . . . . . Our experimental investigation was carried out on such a Magnetically Melt Textured (M.M.T.) YBa2Cu3OT-8 sample with Tc -- 90 K in zero field. The critical currents measured on this sample in a 7 Tesla field at 77 K is of order of 104 A/cm 2 [2]. The approximate size of the parallelepiped shape is 1.5 x 1 x 0.4 m m 3. We report here some transverse a.c. susceptibility measurements i.e. with the static field (H) applied perpendicular to the alternative one (ha.c). Such susceptibility experiments have been extensively used to study the dynamical properties of some random anisotropic ferromagnets [3]. For type II superconductors, the principal difference b e t w e e n t r a n s v e r s e and l o n g i t u d i n a l a.c. experiments can be briefly summarised by the following description. The Flux Line Lattice (F.L.L.) created by the static field interacts with the a.c. induced currents which circulates in a layer of thickness equal to the temperature dependent magnetic penetration depth L(T). For transverse a.c. susceptibility measurements, the response comes from the bending of each vortex which corresponds to the collective tilt mode of the F.L.L. In the case of longitudinal a.c. excitation, it is mainly the compressive mode of the F.L.L. which is concerned
0,05 . . . . . . . . . . . . . . . . . . . h., = Z Oe ~,, r = ls8 Ha ± ~ ~ k. . . . . . . . . . . . . --" 0 ,, tI -~~':. .' : : • o °" ~ 0.06 kOe X' " : *: * ~ -0,05 0.5 kOe ," ." ~:" o* ~ * 1 kOe ,, , o, ~ • 2 kOe j,* ." ~5 J -0 1[ - 4 kOe ,,1//j: .: 'I ---~ ~ ~ ' -0 15 80
84
86
. t . 88
.
90 T (K) Fig, 1 : Thermal variations of X' and X" of the transverse a.c. susceptibility for different values of the static field H applied parallely to the mean (~, b ) planes direction of a M. M. T. YBa2Cu3OT~ sample. giving rise also to a collective response (see for example[4]). For all the set of measurements exposed here, ha.c was applied perpendicularly to the mean direction o f the ~-axis (along the sample side o f I mm long) with a constant amplitude of 2 Oe. Only the low frequency range was investigated (f<1000 Hz) and we s h o w first on Fig.1 t y p i c a l measurements of the real Z' and imaginary part Z" of the transverse a.c. susceptibility. Such results were obtained at f = 158 Hz for different values o f the static field H which is applied perpendicularly to the mean direction of the ~-axis (within a few degrees). As for the case o f longitudinal susceptibility measurements, )C" exhibits a well defined maximum at a temperature T*(H) whereas
0921-4534/94/$07.00 © 1994 Elsevier Science B.V. All rights reserved. SSDI 0921-4534(94)02157-0 -
82
3184
,~ Filippi et a L / P h y s i c a C 235-240 (1994) 3183 ~ 3184
Z' varies monotonously. This maximum defines a transverse irreversible line in the Field-Temperature plane. The best fit of this line (Fig.2) is given by the following power law : H*(T) = a//(1-T/Tc) 2 with a//(158Hz) --- 940 Tesla for the static field applied parallely to the mean (~, b) planes direction. The value o f T c ( ~ 89.8 K) has been determined independently from the extrapolation of the temperature dependence of the onset of dissipation as a function of the static field H (Fig.2). This line can be connected with the formation of vortices at the upper critical field Hc2//parallel to the mean (~, b) planes direction. Such an interpretation cannot be done without having in mind that the upper critical field Hc2 characterises the nucleation of superconductivity in an homogeneous bulk. In the case o f M.M.T. YBa2Cu307_ 8 samples other non-superconducting phases are generally present like Y2BaCuO 5 precipitates at a concentration of the order of 20 % [2]. The presence in the bulk of I n s u l a t i n g / S u p e r c o n d u c t i n g interfaces o f size distributed precipitates can reasonably call into question the use of the "homogeneous description". We will not consider this aspect here, the same measurements done in YBa2Cu307_5 crystal giving similar results but with a different power law for the irreversible line [5]. The temperature dependence of an effective Hc2//(T) has been then extracted from the ~" measurements (Fig.2). As we can see, a linear variation of Hc2//(T) is obtain near T c with a slope approximately equal to -0.3 Tesla/Kelvin. This low value can be explained not only by a disorientation o f the static field but also by the microstructure of the textured sample. We now try to discuss briefly about the physical meaning of the parabolic variation of the maximum of Z" shown on Fig.2. As for longitudinal a.c. m e a s u r e m e n t s (see for example [6]), the "reversible" range in the (H,T) diagram is reduced in the two following cases : When the frequency is increased, a//(980Hz) = 1200 Tesla, and when the static field is parallel to the mean direction of the (fi, b) planes, a L(980Hz) --- 825 Tesla. Theses variations o f the temperature dependence of the irreversible line H*(T) are qualitatively similar to those observed in longitudinal a.c. measurements [6]. As in this case, we can then interpret the transverse irreversible lines shown on Fig.2 in the framework of the thermally activated flux-creep model which combines both pinning and flux flow
5
.
.
.
.
i
.
.
.
.
i
, 7
,
,
158 Hz, H//
p
.
.
.
.
7
.
.
.
.
ilha.c. = 2 0 e / ]
0 Hz, H//
©
1
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87.5
~~:> "
Nc2, T)
I
"~
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88
88.5 89 89.5 90 Y (K) Fig.2 : The solid line represent the linear fit of the variation of the onset of appearance of dissipation for static field applied parallely to the mean direction of (~, b ) planes. The dashed lines show the parabolic fit of variations of the maximum of dissipation for different set of measurements.
of vortices. But for our measurements we must consider a "transverse" critical state defined by the bending of flux line [5]. Acknowledgements
:
The authors would like to thank R. Weber for his help during the experiment and the Region Rh6ne-Alpes for their financial support. References :
[1] D. Braithwaite, D. Bourgault, N. Schopohl, R. Tournier, J.M. Barbut, and J. C. Vallier, J. Low Temp. Phys. 92, (1993), 295. [2] M. R. Lees, D. Bourgault, D. Braithwaite, P. de Rango, P. Lejay, A. Sulpice and R. Tournier, Physica C 191 (1992)414. [3] B. Barbara, B. Dieny and J. Filippi, "Relaxation in Complex Systms and Related Topics", Ed. by !. A. Campbell and C. Giovannella (Plenum Press, New York, 1990) 31. [4] E.H. Brandt, Vortices in Superfluids, NATO Advanced Study Institute, July 19-31 1993, in Carg~se, Corsica. [5] P. Pugnat, J. Filippi and B. Barbara, to be published. [6] A. P. Malozemoff, in "Physical properties of High Temperature Superconductors", Ed. D. Ginsberg (World Scientific, Singapore, 1988) 71.