Gc. Han et al., MAGNETIZATION AND INSTABILITY IN MELT-TEXTURED YBA2CU3O7 AT LOW-TEMPERATURE AND HIGH FIELDS UP TO 23 T, Physica. C, Superconductivity, 274(1-2), 1997, pp. 33-38
Magnetisation loops of QMG-processed bulk YBa2Cu3O7 were measured at 4
.2 K in fields up to 23 T using a new vibrating sample magnetometer (V
SM) combined with a hybrid magnet. J(c) characteristics were derived f
rom the measured magnetisation curves using the Bean critical state mo
del. Flux jumps, which were often observed in magnetisation measuremen
ts for high-J(c) bulk samples at low temperature, were not observed in
these measurements. Magnetisation loops measured by conventional VSM
and by SQUID for the same sample show that flux jumps appear even at a
lower field sweep rate, The magnetic instability depends on the measu
ring conditions. These results suggest that the flux jumps may be indu
ced not only by poor heat conductivity from a sample to its surroundin
gs in SQUID, but also by the larger vibration amplitude in conventiona
l VSM, Using conventional VSM the dependence of the flux jump on field
sweep rates was also measured from 15 to 0.75 T/min. The field at fir
st flux jump increases with decreasing sweep rate.