Influence of magnetic fields on the diamagnetism and the microwave absorption of Gd1+xBa2−xCu3O7 compounds

Abstract Applied static fields increase the width of the diamagnetic susceptibility χ ' ( T ) transition and decrease the irreversibility line temperature T m ( H ): those effects which can be related to intergrain and interplane couplings are amplified by the x concentration for which there is also a decrease of T c related probably to the annihilation of O − holes. The microwave absorption for v = 9 GHz starts at T c and increases below T c ; its field derivative goes through a maximum at a low critical field of type H c 1 and the amplitude of this peak decreases near T c and T = 0 while there is a maximum at T =80 K for x = 0 but at T = 40 K for x ⩾ 0.1 which indicates that x favours a decoupling of CuO 2 planes; all these results can be related to microwave field induced currents.