- Email: [email protected]
Fishtail and flux creep phenomena in the cubic (K, Ba)BiO3 high Tc superconductor
PHYSICA Ii Physica C 282-287
ELSEVIEK
(1997) 2207-2208
Fishtail and flux creep phenomena in the cubic (K, Ba)Bi03
high TC
superconductor T.Klein,
W.Harneit,
aLEPES
- CNHS,
L.Baril,
J.Marcus
and C.Escribe
BP 166, 38042 Grenoble
Filippini
a
Cedex 9, France
The vortex dynamics in the cubic (K, Ba)BiOs superconductor (T, - 3OK) have been investigated by transport and magnetization measurements. We show that, close to the vortex glass transition line, the p exponent characteristic of the creep phenomena (U - J-‘) presents a strong temperature and magnetic field dependence. We also show that this system presents a pronounced “fishtail” effect in the magnetization curves. The magnetic field dependence of the J deduced from this experiment is discussed.
The equilibrium H - T phase diagram of the high T, oxides is particularly rich as many different vortex phases have been predicted and probed by various experimental techniques (for an extensive review see [l]). Similarly, despite much smaller thermal fluctuations, a liquid to glass transition has been observed in the cubic (I<, Ba)BiOs superconductor (T, - 3010 [2]. In the solid phase, the dissipation process is controlled by thermal activation of the flux lines out of pinning sites and the corresponding electrical field can be written as : E - ezp(-U(J,
H,T)/kT).
0.6
0.7
0.8
0.9
1
T/Q
(1)
where U - Uc(Je/J)fl has been predicted both by the collective pinning [l] (l/7 < p < 5/2, depending on the size of the moving vortex bundle) and by the vortex glass [3] (p < 1) theories. Correspondingly, the current decay at “long” waiting times will be given by : J(t, B) - Jo/[lcTln(t/to)/U,]“~,
zl_
(2)
(J(t, B) - Jo/[1 + ($cT/Uu)ln(t/tu)]“” has been proposed close to to). Transport (for current densities ranging from 3104 to 2107 A.m2) and magnetization (down to 2K and up to 30T) measurements have been performed on electrochemically grown (Ii, Ba)BiOs single crystals. The influence of the field sweeping rate on the magnetic hysteresis loops has been checked by varying the time scale from 10s4s (Pulsed Fields) to 104s (SQUID). 0921-4534/97/%17.00 0 Elsevier Science B.V. All rights reserved. PI1 sO921-4534(97)01255-O
Figure 1. Temperature dependence of the p coefficient (see text for detail) for different magnetic field values. The lines are guides to the eyes.
The transport data have been analyzed using Eq.(l) [4] and the corresponding p values have been reported on Fig.1. As shown, ~1 is strongly temperature and magnetic field dependent tending towards N 0.2 as the vortex-glass transition line is approached. A similar behavior has also been observed in cuprates using both transport [5] and magnetization [6] measurements. Such a feature can not be accounted for using the standard elastic creep theories but may be related to the proximity of the vortex glass transition. Far enough from this transition, one may then expect to find a temperature and field in-
2208
7: Klein et al. /Physica
dependent CLvalue as suggested by the plateau observed in the magnetization decay of cuprates [7] and (K, Ba)BiOs samples [8] (according to Eq.(2) S = -l/p./n(t/tc) - 2 - 4% whatever the sample [9]). Another unexpected feature is the “fishtail” effect which has been observed in the magnetization curves of most of the high T, oxides [7]. As shown on Fig.2 such a “fishtail” effect is also obcompound from 2Ii served in the (I{, Ba)BiOs to 2411. Despite the very different time scales involved in our experimental techniques, the J(B) curves perfectly superpose at low temperature [lo] indicating that, far enough from the vortexglass transition line, creep effects do not affect the shape of the JusB curves. The “fishtail” then disappears for long waiting times (SQUID experiment) above 24K (T/Te - 0.75) suggesting that the creep gets very inhomogeneous (i.e. field dependent) close to the vortex-glass transition.
C 282-287 (1997) 2207-2208
in good agreement with the experimental data see inset of Fig.2 - (in this regime p - 5/2 [l]). The “fishtail” may thus be related in a change in the vortex structure (i.e. in Jo and CTc) as recently suggested by Ertas and Nelson [lo]. The situation gets much more complicated close to the vortex-glass transition line where the p coefficient in Eq.(2) gets field (and temperature) dependent (see Fig.1). Despite much smaller thermal fluctuations and a perfectly 3D structure, the (I<, Ba)BiOs superconductor presents a H - T phase diagram which is very similar to the one that has been observed We have shown that the in high T, cuprates. ~1 coefficient (U - J-p) presents a strong temperature and field dependence close to the vortex glass transition line. Far enough from this transition line the magnetic field dependence of the “critical” current deduced from the width of the magnetization loops is in good agreement with creep effects in the so-called small bundle regime. We would like to thank D.Feinberg for very fruitful discussions. REFERENCES G. Blatter, M.V. Feigel’man, A.I. Larkin and V.M. Vinokur Rev. of Mod. Phys. 66 1125 (1994). L. Baril, C. Escribe-Filippini, 2. T. Klein, J. Marcus and A.G.M. Jansen Phys. Rev. B 53 9337 (1996). M.P.A. Fisher and D.A. Huse, 3. D. Fisher, Phys. Rev. B 43 130 (1991). and C. Escribe4. L. Baril, T. Klein, J.Marcus Filippini Phys. Rev. B 54 16058 (1996). and R.H. Koch, 5. C. Dekker, W. Eidelloth, Phys. Rev. Lett. 68 3347 (1992). 6. Y. Abulafia et al. Phys. Rev. L&t. 77 1596 (1996). A.P. Malozemoff and A. 7. Y. Yeshurun, Shaulov Rev. of Mod. Phys. 68 911 (1996). 8. W. Harneit et al., to be published. Pbys. Rev. 9. A.P. Malozemoff and P.A.Fisher B 42 6784 (1990), 10. W. Harneit et al. Physica C. 267 270 (1996). 11. D. Ertas and D.R. Nelson Physica C. 272 79 (1996). 1.
0
5
10
15
B P-I
Figure 2. Magnetization curves using a pulsed field experiment at different temperatures. In the inset : JvsB3f2 in a semi-log scale.
Indeed, following Eq.(2), a constant p value will lead to J(B) - Jo(B).Uo(B)“” which would then be directly related to the magnetic field dependence of Jo and Ilo. In the socalled small bundle regime Jo - ezp(-(B/Bo)3/2) and UO and one would thus expect : e+p( B/Bo)3/2 J(B) N ev[--( rz’ ,, ) .(B/Bo)~/~]
ELSEVIEK
(1997) 2207-2208
Fishtail and flux creep phenomena in the cubic (K, Ba)Bi03
high TC
superconductor T.Klein,
W.Harneit,
aLEPES
- CNHS,
L.Baril,
J.Marcus
and C.Escribe
BP 166, 38042 Grenoble
Filippini
a
Cedex 9, France
The vortex dynamics in the cubic (K, Ba)BiOs superconductor (T, - 3OK) have been investigated by transport and magnetization measurements. We show that, close to the vortex glass transition line, the p exponent characteristic of the creep phenomena (U - J-‘) presents a strong temperature and magnetic field dependence. We also show that this system presents a pronounced “fishtail” effect in the magnetization curves. The magnetic field dependence of the J deduced from this experiment is discussed.
The equilibrium H - T phase diagram of the high T, oxides is particularly rich as many different vortex phases have been predicted and probed by various experimental techniques (for an extensive review see [l]). Similarly, despite much smaller thermal fluctuations, a liquid to glass transition has been observed in the cubic (I<, Ba)BiOs superconductor (T, - 3010 [2]. In the solid phase, the dissipation process is controlled by thermal activation of the flux lines out of pinning sites and the corresponding electrical field can be written as : E - ezp(-U(J,
H,T)/kT).
0.6
0.7
0.8
0.9
1
T/Q
(1)
where U - Uc(Je/J)fl has been predicted both by the collective pinning [l] (l/7 < p < 5/2, depending on the size of the moving vortex bundle) and by the vortex glass [3] (p < 1) theories. Correspondingly, the current decay at “long” waiting times will be given by : J(t, B) - Jo/[lcTln(t/to)/U,]“~,
zl_
(2)
(J(t, B) - Jo/[1 + ($cT/Uu)ln(t/tu)]“” has been proposed close to to). Transport (for current densities ranging from 3104 to 2107 A.m2) and magnetization (down to 2K and up to 30T) measurements have been performed on electrochemically grown (Ii, Ba)BiOs single crystals. The influence of the field sweeping rate on the magnetic hysteresis loops has been checked by varying the time scale from 10s4s (Pulsed Fields) to 104s (SQUID). 0921-4534/97/%17.00 0 Elsevier Science B.V. All rights reserved. PI1 sO921-4534(97)01255-O
Figure 1. Temperature dependence of the p coefficient (see text for detail) for different magnetic field values. The lines are guides to the eyes.
The transport data have been analyzed using Eq.(l) [4] and the corresponding p values have been reported on Fig.1. As shown, ~1 is strongly temperature and magnetic field dependent tending towards N 0.2 as the vortex-glass transition line is approached. A similar behavior has also been observed in cuprates using both transport [5] and magnetization [6] measurements. Such a feature can not be accounted for using the standard elastic creep theories but may be related to the proximity of the vortex glass transition. Far enough from this transition, one may then expect to find a temperature and field in-
2208
7: Klein et al. /Physica
dependent CLvalue as suggested by the plateau observed in the magnetization decay of cuprates [7] and (K, Ba)BiOs samples [8] (according to Eq.(2) S = -l/p./n(t/tc) - 2 - 4% whatever the sample [9]). Another unexpected feature is the “fishtail” effect which has been observed in the magnetization curves of most of the high T, oxides [7]. As shown on Fig.2 such a “fishtail” effect is also obcompound from 2Ii served in the (I{, Ba)BiOs to 2411. Despite the very different time scales involved in our experimental techniques, the J(B) curves perfectly superpose at low temperature [lo] indicating that, far enough from the vortexglass transition line, creep effects do not affect the shape of the JusB curves. The “fishtail” then disappears for long waiting times (SQUID experiment) above 24K (T/Te - 0.75) suggesting that the creep gets very inhomogeneous (i.e. field dependent) close to the vortex-glass transition.
C 282-287 (1997) 2207-2208
in good agreement with the experimental data see inset of Fig.2 - (in this regime p - 5/2 [l]). The “fishtail” may thus be related in a change in the vortex structure (i.e. in Jo and CTc) as recently suggested by Ertas and Nelson [lo]. The situation gets much more complicated close to the vortex-glass transition line where the p coefficient in Eq.(2) gets field (and temperature) dependent (see Fig.1). Despite much smaller thermal fluctuations and a perfectly 3D structure, the (I<, Ba)BiOs superconductor presents a H - T phase diagram which is very similar to the one that has been observed We have shown that the in high T, cuprates. ~1 coefficient (U - J-p) presents a strong temperature and field dependence close to the vortex glass transition line. Far enough from this transition line the magnetic field dependence of the “critical” current deduced from the width of the magnetization loops is in good agreement with creep effects in the so-called small bundle regime. We would like to thank D.Feinberg for very fruitful discussions. REFERENCES G. Blatter, M.V. Feigel’man, A.I. Larkin and V.M. Vinokur Rev. of Mod. Phys. 66 1125 (1994). L. Baril, C. Escribe-Filippini, 2. T. Klein, J. Marcus and A.G.M. Jansen Phys. Rev. B 53 9337 (1996). M.P.A. Fisher and D.A. Huse, 3. D. Fisher, Phys. Rev. B 43 130 (1991). and C. Escribe4. L. Baril, T. Klein, J.Marcus Filippini Phys. Rev. B 54 16058 (1996). and R.H. Koch, 5. C. Dekker, W. Eidelloth, Phys. Rev. Lett. 68 3347 (1992). 6. Y. Abulafia et al. Phys. Rev. L&t. 77 1596 (1996). A.P. Malozemoff and A. 7. Y. Yeshurun, Shaulov Rev. of Mod. Phys. 68 911 (1996). 8. W. Harneit et al., to be published. Pbys. Rev. 9. A.P. Malozemoff and P.A.Fisher B 42 6784 (1990), 10. W. Harneit et al. Physica C. 267 270 (1996). 11. D. Ertas and D.R. Nelson Physica C. 272 79 (1996). 1.
0
5
10
15
B P-I
Figure 2. Magnetization curves using a pulsed field experiment at different temperatures. In the inset : JvsB3f2 in a semi-log scale.
Indeed, following Eq.(2), a constant p value will lead to J(B) - Jo(B).Uo(B)“” which would then be directly related to the magnetic field dependence of Jo and Ilo. In the socalled small bundle regime Jo - ezp(-(B/Bo)3/2) and UO and one would thus expect : e+p( B/Bo)3/2 J(B) N ev[--( rz’ ,, ) .(B/Bo)~/~]