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Transverse magnetization of a rotating YBa2Cu3O7−δ crystal near Tc
PHYSICA
Physica B 194-196 (1994) 2055-2056 North-Holland
T R A N S V E R S E M A G N E T I Z A T I O N OF A R O T A T I N G YBa2Cu307_ 5 C R Y S T A L N E A R T c. P. Pugnat, G. Fillion, S. Khene*, H. Noel**, P. Schuster*** and B. Barbara Laboratoire de magnrtisme Louis N6el, CNRS, B.P. 166, 38042 Grenoble, FRANCE *Laboratoire de magnrtisme, B.P. 12, E1-Hadjar, Annaba, ALGERIE **Laboratoire de chimie minrrale B, Universit6 de Rennes 1, CNRS, 35042 Rennes Cedex, FRANCE ***Merlin Gerin, Drpartement des Recherches Grnrrales, Rue Henri Tarze, 38050 Grenoble, FRANCE. The transverse component of the magnetization of a YBa2Cu307_ fi single crystal (Tc = 91K) has been investigated by slowly rotating the sample in a magnetic field. Close to T c (Tc-T = 0.5K), a linear decrease with applied field in the maximum of this transverse magnetization was observed, according to the 3-Dimensional Anisotropic Ginzburg Landau mean field theory. In spite of this high temperature, our measurements show some irreversibility effects particularly when the field is oriented close to the (a,b) planes direction.
H i g h T e m p e r a t u r e c o p p e r oxide Superconductors (H.T.S.) structures can be described as a stack of more or less coupled superconducting cells made up o f one or more CuO2 planes. Such a layered stucture gives rise to anisotropic physical properties and contributes with the very short coherence lengths and the high value o f T c to enhance the effects of fluctuations [ 1]. Our measurements were carried out using a YBa2Cu307_ 5 s i n g l e crystal with zero field transition temperature o f 91 K prepared by solid state reaction and mineral process [2]. To avoid the effects of shape anisotropy, a cylindrical form was adopted for the sample (diameter (I) - 0.85mm and length 1 = 1.9mm) with c-axis and (a,b) planes in the circular section. Measurements were made using a double SQUID equipped with a pair o f orthogonal p i c k - u p coils which allow one to measure s i m u l t a n e o u s l y the two c o m p o n e n t s o f the magnetization vector M L and MT (respectively the c o m p o n e n t parallel and perpendicular to the magnetic field direction). The results, for both components will be given elsewhere [3]. We report hereby the variation of MT for Tc-T = 0.5 K as a function of magnetic field for continuous variation of the angle 0 between the applied field and the eaxis. Rotation velocity was equal to 0.3°/s which gives us an angular resolution of 0.3 degrees. The angular variations o f the magnetization transverse c o m p o n e n t MT are given in Fig. 1 for different applied fields (H = 0.5, 1, 2 kOe) at a fixed temperature T = 90.5 K. We can see a sharp increase when the field is close to the layers direction. The irreversible transverse magnetization defined by the relation MTir(0) = {MT(0+) - MT(0--) }/2 where
0.8
•
H:O.
Oe
0.6 0,4 0.2
o -0.2 -0.4
.
.
.
.
.
.
.
.
i , ~ , ,
45
. . . .
I
.
90
.
.
.
.
.
.
.
i
.
.
.
.
.
.
.
.
135
80
Theta (degrees) Fig.1 : Transverse magnetization versus the angle 0 between the magnetic field and the c-axis for T = 90.5 K. MT(0+) and MT(0-) are the t r a n s v e r s e magnetization for 0 varying in b o t h directions, shows the irreversible aspect of this sharp maximum (intrinsic pinning o f vortices) [3]. Indeed, the reversible transverse magnetization obtained from MTrev(0) = {MT(0+) + MT(0--)}/2 does not show any anomaly throughout the angular range where the field is close to the (a,b) planes direction (Fig.2). There are mainly three experimental manifestations of irreversibility on the transverse magnetization : - a sharp maximum for 0 close to the 90°value that we ascribe to a lock-in transition [4], - a non-zero mean value integrated over one period, and - a lag angle of the field (too small to be measured for field H > 2kOe).
0921-4526/94/$07.00 © 1994 - Elsevier Science B.V. All rights reserved S S D I 0921-4526(93)1660-E
2056 The angular variation of the reversible part of the transverse m a g n e t i z a t i o n MTrev (Fig.2) can be interpreted using the f o l l o w i n g result of the 3D i m e n s i o n a l A n i s o t r o p i c Ginzburg Landau mean field theory (3-D.A.G.L.) [5] : MTrev(OB)
= M
sin(2eB) TO ~(~B~B)
(1- H-H~ ~)
)
(1)
where ~(0) = (sin2e + 72cos2e)1/2, eB is the angle between vortices and the e-axis (OB=O), MT0 is a p a r a m e t e r independent of the angle, Hc2// is the upper critical field parallel to the (a,b) planes and 7 is the square root o f the ratio o f effective masses. For H = 2 and lkOe, the fitting parameters obtained at T c - T = 0.5 K are 7--- 8.1 and 10.5 respectively with H c 2 / / = 29 kOe. In the case of H = 0.5kOe, a higher value for the ratio of effective masses was obtained (7 =16), but this field value is certainly b e y o n d the range o f validity o f the 3-D.A.G.L. theory (Fig.3). Such results may also suggest some 7 field dependence. 1
x t~
0.8
E> 0.6 I-
~>
0.4
~
O.2 0
22.5
45
67.5
0.6
~,
, ................
A
0.5 o
-,~E v X
0.4 ~ 0.3
E o.2 0.1
. . . .
0
I
,
, ~
2
i
I
L
4
6
8
. . . .
0
H(kOe)
Fig.3 : Maximum amplitude of the whole transverse magnetization MTmax versus the magnetic field. The linear decrease is observed for field H > 0.5kOe. Error bars indicate the dispersion of our measurements. The difference between the whole MTmax and its reversible part is included in the size of error bars. a p p r o a c h e s the critical mean field Hc2(T,0max ) (Fig.3) according to (1). As this m a x i m u m appears for the angle 0max = 78 ° which is only weakly field d e p e n d e n t , then by t a k i n g 7 = 8.1 we find Hc2//(T=90.5K) = 29 kOe, in perfect agreement with the value o b t a i n e d above. This gives for temperatures close to T c, d H c 2 / / ] d T = -5.8+._0.5 Tesla/K. From the slope o f Fig.3, we could also determine the G.L. parameter for magnetic field parallel to the (a,b) planes, ~ / / = 140 + 20. All the parameters obtained from our m e a s u r e m e n t s are consistent with literature values for YBa2Cu3OT_8 [2],[6] and therefore strongly suggest the validity of the 3-D.A.G.L mean field theory for the field and temperature range investigated.
9O
Theta (degrees) F i g . 2 : Reversible transverse magnetization versus the angle e between the magnetic field and the e-axis for T = 90.5 K and H = 1 kOe. Data was fitted with formula (1).
Acknowledgements
The authors would like to thank the R6gion Rh6ne Alpes for their financial support. References
The m a x i m u m amplitude of the whole transverse m a g n e t i z a t i o n M T m a x ( w e a k l y a f f e c t e d by i r r e v e r s i b i l i t y ) was plotted as a function o f the applied field H (Fig.3). As the temperature stability was included in the approximate range o f + 0.03 K, this gave rise to s o m e d i s p e r s i o n on MTmax measurements. Mean value m e a s u r e d for several periods was then considered to give better results. For T = 90.5 K, a linear decrease in the maximum of the transverse magnetization was observed, when H
"
:
[1] U. Welp et al. Phys.Rev.Lett. 67 (1991) 3180. [2] J. L. Tholence et al. Studies of high temperature superconductors, Vol.6, ed. by A. Narlikar (Nova Science Publishers, New York 1990) p.37. [3] P.Pugnat et al. to be published. [4] P. Pugnat et al. J.M.C.3 de la Soci6t6 Franqaise de Physique (Villeneuve d'Ascq, 1992) and to be published. [5] V. G. Kogan et al. Phys.Rev.B 24 (1981) 2497. [6] U. Welp et al. Phys.Rev.Lett. 62 (1989) 1908.
Physica B 194-196 (1994) 2055-2056 North-Holland
T R A N S V E R S E M A G N E T I Z A T I O N OF A R O T A T I N G YBa2Cu307_ 5 C R Y S T A L N E A R T c. P. Pugnat, G. Fillion, S. Khene*, H. Noel**, P. Schuster*** and B. Barbara Laboratoire de magnrtisme Louis N6el, CNRS, B.P. 166, 38042 Grenoble, FRANCE *Laboratoire de magnrtisme, B.P. 12, E1-Hadjar, Annaba, ALGERIE **Laboratoire de chimie minrrale B, Universit6 de Rennes 1, CNRS, 35042 Rennes Cedex, FRANCE ***Merlin Gerin, Drpartement des Recherches Grnrrales, Rue Henri Tarze, 38050 Grenoble, FRANCE. The transverse component of the magnetization of a YBa2Cu307_ fi single crystal (Tc = 91K) has been investigated by slowly rotating the sample in a magnetic field. Close to T c (Tc-T = 0.5K), a linear decrease with applied field in the maximum of this transverse magnetization was observed, according to the 3-Dimensional Anisotropic Ginzburg Landau mean field theory. In spite of this high temperature, our measurements show some irreversibility effects particularly when the field is oriented close to the (a,b) planes direction.
H i g h T e m p e r a t u r e c o p p e r oxide Superconductors (H.T.S.) structures can be described as a stack of more or less coupled superconducting cells made up o f one or more CuO2 planes. Such a layered stucture gives rise to anisotropic physical properties and contributes with the very short coherence lengths and the high value o f T c to enhance the effects of fluctuations [ 1]. Our measurements were carried out using a YBa2Cu307_ 5 s i n g l e crystal with zero field transition temperature o f 91 K prepared by solid state reaction and mineral process [2]. To avoid the effects of shape anisotropy, a cylindrical form was adopted for the sample (diameter (I) - 0.85mm and length 1 = 1.9mm) with c-axis and (a,b) planes in the circular section. Measurements were made using a double SQUID equipped with a pair o f orthogonal p i c k - u p coils which allow one to measure s i m u l t a n e o u s l y the two c o m p o n e n t s o f the magnetization vector M L and MT (respectively the c o m p o n e n t parallel and perpendicular to the magnetic field direction). The results, for both components will be given elsewhere [3]. We report hereby the variation of MT for Tc-T = 0.5 K as a function of magnetic field for continuous variation of the angle 0 between the applied field and the eaxis. Rotation velocity was equal to 0.3°/s which gives us an angular resolution of 0.3 degrees. The angular variations o f the magnetization transverse c o m p o n e n t MT are given in Fig. 1 for different applied fields (H = 0.5, 1, 2 kOe) at a fixed temperature T = 90.5 K. We can see a sharp increase when the field is close to the layers direction. The irreversible transverse magnetization defined by the relation MTir(0) = {MT(0+) - MT(0--) }/2 where
0.8
•
H:O.
Oe
0.6 0,4 0.2
o -0.2 -0.4
.
.
.
.
.
.
.
.
i , ~ , ,
45
. . . .
I
.
90
.
.
.
.
.
.
.
i
.
.
.
.
.
.
.
.
135
80
Theta (degrees) Fig.1 : Transverse magnetization versus the angle 0 between the magnetic field and the c-axis for T = 90.5 K. MT(0+) and MT(0-) are the t r a n s v e r s e magnetization for 0 varying in b o t h directions, shows the irreversible aspect of this sharp maximum (intrinsic pinning o f vortices) [3]. Indeed, the reversible transverse magnetization obtained from MTrev(0) = {MT(0+) + MT(0--)}/2 does not show any anomaly throughout the angular range where the field is close to the (a,b) planes direction (Fig.2). There are mainly three experimental manifestations of irreversibility on the transverse magnetization : - a sharp maximum for 0 close to the 90°value that we ascribe to a lock-in transition [4], - a non-zero mean value integrated over one period, and - a lag angle of the field (too small to be measured for field H > 2kOe).
0921-4526/94/$07.00 © 1994 - Elsevier Science B.V. All rights reserved S S D I 0921-4526(93)1660-E
2056 The angular variation of the reversible part of the transverse m a g n e t i z a t i o n MTrev (Fig.2) can be interpreted using the f o l l o w i n g result of the 3D i m e n s i o n a l A n i s o t r o p i c Ginzburg Landau mean field theory (3-D.A.G.L.) [5] : MTrev(OB)
= M
sin(2eB) TO ~(~B~B)
(1- H-H~ ~)
)
(1)
where ~(0) = (sin2e + 72cos2e)1/2, eB is the angle between vortices and the e-axis (OB=O), MT0 is a p a r a m e t e r independent of the angle, Hc2// is the upper critical field parallel to the (a,b) planes and 7 is the square root o f the ratio o f effective masses. For H = 2 and lkOe, the fitting parameters obtained at T c - T = 0.5 K are 7--- 8.1 and 10.5 respectively with H c 2 / / = 29 kOe. In the case of H = 0.5kOe, a higher value for the ratio of effective masses was obtained (7 =16), but this field value is certainly b e y o n d the range o f validity o f the 3-D.A.G.L. theory (Fig.3). Such results may also suggest some 7 field dependence. 1
x t~
0.8
E> 0.6 I-
~>
0.4
~
O.2 0
22.5
45
67.5
0.6
~,
, ................
A
0.5 o
-,~E v X
0.4 ~ 0.3
E o.2 0.1
. . . .
0
I
,
, ~
2
i
I
L
4
6
8
. . . .
0
H(kOe)
Fig.3 : Maximum amplitude of the whole transverse magnetization MTmax versus the magnetic field. The linear decrease is observed for field H > 0.5kOe. Error bars indicate the dispersion of our measurements. The difference between the whole MTmax and its reversible part is included in the size of error bars. a p p r o a c h e s the critical mean field Hc2(T,0max ) (Fig.3) according to (1). As this m a x i m u m appears for the angle 0max = 78 ° which is only weakly field d e p e n d e n t , then by t a k i n g 7 = 8.1 we find Hc2//(T=90.5K) = 29 kOe, in perfect agreement with the value o b t a i n e d above. This gives for temperatures close to T c, d H c 2 / / ] d T = -5.8+._0.5 Tesla/K. From the slope o f Fig.3, we could also determine the G.L. parameter for magnetic field parallel to the (a,b) planes, ~ / / = 140 + 20. All the parameters obtained from our m e a s u r e m e n t s are consistent with literature values for YBa2Cu3OT_8 [2],[6] and therefore strongly suggest the validity of the 3-D.A.G.L mean field theory for the field and temperature range investigated.
9O
Theta (degrees) F i g . 2 : Reversible transverse magnetization versus the angle e between the magnetic field and the e-axis for T = 90.5 K and H = 1 kOe. Data was fitted with formula (1).
Acknowledgements
The authors would like to thank the R6gion Rh6ne Alpes for their financial support. References
The m a x i m u m amplitude of the whole transverse m a g n e t i z a t i o n M T m a x ( w e a k l y a f f e c t e d by i r r e v e r s i b i l i t y ) was plotted as a function o f the applied field H (Fig.3). As the temperature stability was included in the approximate range o f + 0.03 K, this gave rise to s o m e d i s p e r s i o n on MTmax measurements. Mean value m e a s u r e d for several periods was then considered to give better results. For T = 90.5 K, a linear decrease in the maximum of the transverse magnetization was observed, when H
"
:
[1] U. Welp et al. Phys.Rev.Lett. 67 (1991) 3180. [2] J. L. Tholence et al. Studies of high temperature superconductors, Vol.6, ed. by A. Narlikar (Nova Science Publishers, New York 1990) p.37. [3] P.Pugnat et al. to be published. [4] P. Pugnat et al. J.M.C.3 de la Soci6t6 Franqaise de Physique (Villeneuve d'Ascq, 1992) and to be published. [5] V. G. Kogan et al. Phys.Rev.B 24 (1981) 2497. [6] U. Welp et al. Phys.Rev.Lett. 62 (1989) 1908.