FLUX CREEP AND FLUX FLOW FOR THALLIUM CERAMICS IN A PULSED MAGNETIC-FIELD

The resistive properties of Tl-ceramics with T(c)\rho = 0 = 115 K were investigated in a pulsed magnetic field (B) up to 30 T and in the temperature range of 4.2 K < T < 140 K. It was shown that the character of the field dependence of the resistance differs qualitatively in high- and low-temperature regions. At low (T less-than-or-similar-to 80 K) temperatures the dynamic magnetoresistance arising in the sample is analogous to that observed earlier in LaSrCuO [1] and YBaCuO [2] ceramics. This magnetoresistance is defined by the magnetic field variation rate B = dB/dt and leads to the appearance of a rho minimum at the maximum of the magnetic field pulse, i.e. at B = 0. In the region of high temperatures (80 K less-than-or-similar-to T < T(c)) or magnetic fields (at T greater-than-or-similar-to 60 K) the sample resistance rises monotonically with B increase, and dynamic resistance is not observed. In this temperature range the existence of a scaling relation B* proportional-to (1 - T*/T(c))3/2 is shown (here B* and T* meet the condition k = rho(B*, T*)/rho(n)(T*) = const) for the ceramics resistance rho(B, T), which can be represented as rho/rho(n) = (B/B0)1/2(1 - T/T(c))-3/4. An estimate for the upper critical field B(c2)(0) congruent-to B0 = 1030 +/- 40 T is obtained.