Determination of the intragrain irreversible temperature T g irr of Bi(2223) superconductor by ESR measurement

We consider our Bi(2223) polycrystalline sample to be made up of superconducting grains which are separated by Josephson junctions. Two characteristic temperatures, i.e. the irreversible temperature T-irr(g) and T-irr(j) of the grains and Josephson junctions should appear as a natural consequence of the electromagnetic theory and irreversible magnetization [1,2]. Macroscopically T-irr(j) and T-irr(g) correspond to the temperature, at which the diamagnetic hysteresis loop and the paramagnetic hysteresis loop disappear respectively [3]. It has been proposed that microwave absorption results from decoupling of grains (Dulcic's model). Extending this model to include temperature dependence of the resistivity rho(T) and the critical current I-c(H, T), we have deduced an expression for microwave absorption. This expression includes a term which is non-zero even after the microwave absorption at low field disappears. We have therefore carried out ESR absorption measurement of our sample from 96 K to 110 K and have found that a broad weak absorption peak does occur in the temperature range T-c > T greater than or equal to 108 K, giving T-irr(g) = 108 K. When T > T-c, such a weak peak disappears. Apart from this finding, the result of low field microwave absorption is qualitatively similar to the results of others.