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Anomalies in low field magnetic response near Tc in layered high temperature superconductors
Physica C 235-240 (1994)3281-3282 North-Holland
PRYSlCA
Anomalies in Low Field Magnetic Response near Temperature Superconductors
in Layered High
A.K. Grover ~,b, N. Goyal ¢, F. Iga b, K, Ino d, N. Aoki d, Y. Yamaguchi b and Y. Nishihara b Tata Institute Of Fundamental Research, Homi Bhabha Road, Bombay 400005, India. b Electrotechnical Laboratory, Tsukuba, Ibaraki 305, Japan. C.A.S. in Physics, Panjab University, Chandigarh 160014, India. a Meiji University, Kawasaki, Kanagawa 216, Japan. Magnetic response at low fields is observed to be hysteretic and anomalous in a JCLS for T*
Bi2212 system, whose unit cell comprises a pair of CuO~ bilayers, is an archetypal of highly anisotropic Josephson Coupled Layered Superconductors (JCLS). Qualitative changes start to occur in the magnetic response of a JCLS at a temperature T* located somewhat below the To(H=0) value and these have been ascribed [1] to the rapid weakening of the Josephson coupling between CuO~. planes (i.e., bilayers in the case of Bi2212). For instance, it has been known [2] that temperature dependent magnetization curves (for H > Hmin) intersect at temperature T*, where AM/ZXIt = 0. For T < T*, A M / A H >0 (as in the mixed state of a reversible type-II superconductor), and for T > T*, A M / A H is negative (i.e., the diamagnetic signal monotonically increases as H increases for H > Hmin). Further, °
E~
H = I00
Oe
-I0
%
o -2°
X
.
BiZZlZ
(HIIo)
o
-40
' "~"
84
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~l
85
I~
J I '
' ' '
[ '
86
' ' $ I ....
I ....
87
t
I ' '
I . . . .
88
Temperature (K)
Figure 1. M-T curves at different H (HI[c)
I ....
89
we have recently reported [1,3] that the magnetic behaviour in Bi2212 (HIIc) undergoes a crossover from one component response (due to strongly coupled quasi 2D planes) to a two component like response over a narrow temperature interval encompassing its T* value. For T* < T < To(0), the weakly coupled planes display behaviour which can be viewed as superposition and interplay between the responses from two components attributable to residual inter planar coupling and the mobile pancake vortices [4] in the 2D planes. In the low field region, the magnetic behaviour is largely dictated by inter planar coupling and is characteristically hysteretic (see, e.g., Fig.4 of [1], as in any type-II superconductor, however, above a certain field value (designated as H2D in [1]), the response due to superconducting fluctuations in 2D planes takes over (i.e., A M / A H < 0). The observed hysteretic behaviour at low field values in isothermal data implies the existence of a host of anomalous looking results in the temperature dependent magnetization data as well. For instance, Fig.1 shows M-T curves in H = 0.13roT, linT and 101aT in our specimen of Bi2212 (H ][c). The curves for 0.13roT and h a t do not appear to intersect, whereas the curve for 10roT intersects them at 85.3K and 85.9K, respectively. In contrast, all M-T curves for 10mT < H < 5T in the same sample intersect at T* = 85.5K (see Fig.1 of [3]). Fig.2 shows M-T curves following different thermomagnetic histories (as indicated by arrows) in a field of 0.13roT. It is apparent that at
0921-4534/94/$07.00© 1994- ElsevierScienceB.V. All rights reserved. SSDI 0921-4534(94)02206-2
A.K. Grover et al./Physica C 235-240 (1994) 3281 3282
3282
Bi2212
I0 ~
(HIIc)
Bi2212 H//c
0.0
(a)
"•
Tw
I
I
I
104
P
20 Hr
Vortex fluid
o
-o.1
] T~D(H}
~ ~"
k
103
E -0.2
"~
.~
' DieouNed 2D
H2D~~e,
&~o
IO i
-0.3
/ ~ / i r "~-'Tcw
-0.4
HsO r\
I0 z
84
/ >'c
85
/
~B56K H--1.30e
Strongly coupled 2D (=3D)
to o 86
87
8B
so
I s2
T > 85.6K, the field cool cool-down magnetization curve ( M F c c ) lies below the corresponding zero field cooled ( M z F c ) curve and this is anomalous. In isothermal data we had earlier recognized that the magnetization values during virgin r a m p up of the field are smaller than those recorded while ramping the field down (cf. curves 1 and 2 in Fig.4 of [1]). We believe that the anomalies, [MFcc(T)[ > [Marc(T)[ and IM(H 1)1 < ] M ( H 1)[, are a consequence of interplay between magnetic responses from the two components as enunciated above. The above anomalies are somewhat analogous to the observation that the transport current density J*~(H) in a ceramic sample depends on the thermomagnetic history of applied H in the same manner as the magnetization behaviour described above [5]. The anomalies in the low field magnetization data appear intrinsic to the occurrence of dimensional crossover phenomenon at T*. Two interrelated inferences which are further apparent from Fig.2 are as follows: (i) FC magnetization is path dependent at low H and (ii) the irreversibility temperature T~ (It) defined by the merger of MFCC curve with MZFC curve is significantly higher than that determined via the merger of MFCW(T) curve with M Z F c ( T ) curve. We would like to correlate the interval T* < T < To(0) over which we see spectacular manifestation of two component response with the interval T~ b < T
Weakly coupled 2D P®~o (-2component}
[ 1' 8 6
I 8s
90
T
Temperature(K) Figure 2. M-T curves along different paths in 1t=0.13 m T (liNe)
i 84
Pob-o
Temperature
(K)
Figure 3. Magnetic phase diagram in our specimen of Bi2212
servation of usual shaped minor hysteresis loop confined to low field values at T > T * inherently implies the existence of supercurrents presumably across the planes. We think that T~ b (where the resistivity within the planes goes to zero) probably marks the transition from weakly coupled to strongly coupled response fi'om 3osephson coupled layers in the magnetization data. In view of above, we have now labeled (see Fig.a) the phase diagram of [3] to summarize all our inferences. The tt2D(T) line defines the limit below which anomalies in magnetic behaviour are observed. One of us (AKG) acknowledges STA of J a p a n for research award for foreign specialists. 1. R e f e r e n c e s 1. A.K. Grover et al., Physica C 220 (1994) 353. 2. P.H. Kes et al., Phys. Rev. Lett. 67 (1991) 2283. 3. Y. Nishihara et al., Proc. on tlTSC (Tsukuba,1993).
ETL workshop
4..J.R. Clem, Phys. Rev. B 43 (1991) 7837. 5. P.K. Mishra et al., Jpn. a. Appl. Phys. Lett. 29 (1990) L1612 and references therein. 6. Y. M. Wan et al., Phys. (1993) 157.
Rev.
Lett.
71
PRYSlCA
Anomalies in Low Field Magnetic Response near Temperature Superconductors
in Layered High
A.K. Grover ~,b, N. Goyal ¢, F. Iga b, K, Ino d, N. Aoki d, Y. Yamaguchi b and Y. Nishihara b Tata Institute Of Fundamental Research, Homi Bhabha Road, Bombay 400005, India. b Electrotechnical Laboratory, Tsukuba, Ibaraki 305, Japan. C.A.S. in Physics, Panjab University, Chandigarh 160014, India. a Meiji University, Kawasaki, Kanagawa 216, Japan. Magnetic response at low fields is observed to be hysteretic and anomalous in a JCLS for T*
Bi2212 system, whose unit cell comprises a pair of CuO~ bilayers, is an archetypal of highly anisotropic Josephson Coupled Layered Superconductors (JCLS). Qualitative changes start to occur in the magnetic response of a JCLS at a temperature T* located somewhat below the To(H=0) value and these have been ascribed [1] to the rapid weakening of the Josephson coupling between CuO~. planes (i.e., bilayers in the case of Bi2212). For instance, it has been known [2] that temperature dependent magnetization curves (for H > Hmin) intersect at temperature T*, where AM/ZXIt = 0. For T < T*, A M / A H >0 (as in the mixed state of a reversible type-II superconductor), and for T > T*, A M / A H is negative (i.e., the diamagnetic signal monotonically increases as H increases for H > Hmin). Further, °
E~
H = I00
Oe
-I0
%
o -2°
X
.
BiZZlZ
(HIIo)
o
-40
' "~"
84
' ~ ....
~l
85
I~
J I '
' ' '
[ '
86
' ' $ I ....
I ....
87
t
I ' '
I . . . .
88
Temperature (K)
Figure 1. M-T curves at different H (HI[c)
I ....
89
we have recently reported [1,3] that the magnetic behaviour in Bi2212 (HIIc) undergoes a crossover from one component response (due to strongly coupled quasi 2D planes) to a two component like response over a narrow temperature interval encompassing its T* value. For T* < T < To(0), the weakly coupled planes display behaviour which can be viewed as superposition and interplay between the responses from two components attributable to residual inter planar coupling and the mobile pancake vortices [4] in the 2D planes. In the low field region, the magnetic behaviour is largely dictated by inter planar coupling and is characteristically hysteretic (see, e.g., Fig.4 of [1], as in any type-II superconductor, however, above a certain field value (designated as H2D in [1]), the response due to superconducting fluctuations in 2D planes takes over (i.e., A M / A H < 0). The observed hysteretic behaviour at low field values in isothermal data implies the existence of a host of anomalous looking results in the temperature dependent magnetization data as well. For instance, Fig.1 shows M-T curves in H = 0.13roT, linT and 101aT in our specimen of Bi2212 (H ][c). The curves for 0.13roT and h a t do not appear to intersect, whereas the curve for 10roT intersects them at 85.3K and 85.9K, respectively. In contrast, all M-T curves for 10mT < H < 5T in the same sample intersect at T* = 85.5K (see Fig.1 of [3]). Fig.2 shows M-T curves following different thermomagnetic histories (as indicated by arrows) in a field of 0.13roT. It is apparent that at
0921-4534/94/$07.00© 1994- ElsevierScienceB.V. All rights reserved. SSDI 0921-4534(94)02206-2
A.K. Grover et al./Physica C 235-240 (1994) 3281 3282
3282
Bi2212
I0 ~
(HIIc)
Bi2212 H//c
0.0
(a)
"•
Tw
I
I
I
104
P
20 Hr
Vortex fluid
o
-o.1
] T~D(H}
~ ~"
k
103
E -0.2
"~
.~
' DieouNed 2D
H2D~~e,
&~o
IO i
-0.3
/ ~ / i r "~-'Tcw
-0.4
HsO r\
I0 z
84
/ >'c
85
/
~B56K H--1.30e
Strongly coupled 2D (=3D)
to o 86
87
8B
so
I s2
T > 85.6K, the field cool cool-down magnetization curve ( M F c c ) lies below the corresponding zero field cooled ( M z F c ) curve and this is anomalous. In isothermal data we had earlier recognized that the magnetization values during virgin r a m p up of the field are smaller than those recorded while ramping the field down (cf. curves 1 and 2 in Fig.4 of [1]). We believe that the anomalies, [MFcc(T)[ > [Marc(T)[ and IM(H 1)1 < ] M ( H 1)[, are a consequence of interplay between magnetic responses from the two components as enunciated above. The above anomalies are somewhat analogous to the observation that the transport current density J*~(H) in a ceramic sample depends on the thermomagnetic history of applied H in the same manner as the magnetization behaviour described above [5]. The anomalies in the low field magnetization data appear intrinsic to the occurrence of dimensional crossover phenomenon at T*. Two interrelated inferences which are further apparent from Fig.2 are as follows: (i) FC magnetization is path dependent at low H and (ii) the irreversibility temperature T~ (It) defined by the merger of MFCC curve with MZFC curve is significantly higher than that determined via the merger of MFCW(T) curve with M Z F c ( T ) curve. We would like to correlate the interval T* < T < To(0) over which we see spectacular manifestation of two component response with the interval T~ b < T
Weakly coupled 2D P®~o (-2component}
[ 1' 8 6
I 8s
90
T
Temperature(K) Figure 2. M-T curves along different paths in 1t=0.13 m T (liNe)
i 84
Pob-o
Temperature
(K)
Figure 3. Magnetic phase diagram in our specimen of Bi2212
servation of usual shaped minor hysteresis loop confined to low field values at T > T * inherently implies the existence of supercurrents presumably across the planes. We think that T~ b (where the resistivity within the planes goes to zero) probably marks the transition from weakly coupled to strongly coupled response fi'om 3osephson coupled layers in the magnetization data. In view of above, we have now labeled (see Fig.a) the phase diagram of [3] to summarize all our inferences. The tt2D(T) line defines the limit below which anomalies in magnetic behaviour are observed. One of us (AKG) acknowledges STA of J a p a n for research award for foreign specialists. 1. R e f e r e n c e s 1. A.K. Grover et al., Physica C 220 (1994) 353. 2. P.H. Kes et al., Phys. Rev. Lett. 67 (1991) 2283. 3. Y. Nishihara et al., Proc. on tlTSC (Tsukuba,1993).
ETL workshop
4..J.R. Clem, Phys. Rev. B 43 (1991) 7837. 5. P.K. Mishra et al., Jpn. a. Appl. Phys. Lett. 29 (1990) L1612 and references therein. 6. Y. M. Wan et al., Phys. (1993) 157.
Rev.
Lett.
71