LOW-TEMPERATURE MAGNETOCALORIC EFFECTS IN DY(1)BA(2)CU(3)O(7-DELTA)AND Y1BA2CU3O7-DELTA HIGH-T-C SINGLE-CRYSTALS

The heat release Qover dot has been measured in high temperature super conductors during and after a change of the external magnetic field mu (0)H(a) less than or equal to 0.5 T applied parallel to the c-axis at 0.1 K less than or equal to T less than or equal to 0.45 K. Two Y123 a nd one Dy123 twinned single crystals were investigated. An analysis of the heat release based on the Bean model and on a model for thin supe rconductors in perpendicular geometry recently proposed by Brandt et a l. has been carried out. During field sweep we measured Qover dot prop ortional to H(a)(2)dH(a)/dt. This dependence can be understood within the Bean model for longitudinal geometry. The critical current densiti es obtained with this method are in good agreement with those from mag netization measurements. We also present measurements, and a first qua ntitative analysis, of dissipation due to the time relaxation of the f lux line lattice after a field sweep. For the heat release a t(-1) dep endence has been found which corresponds to a logarithmic time depende nce of the magnetization. The normalized relaxation rate we obtained i s in agreement with literature values.