CALORIMETRIC STUDY OF NONSUPERCONDUCTING GdBa2Cu3O6+δ

In a recent paper the authors reported calorimetric evidence of an antiferromagnetic transition at T/sub N/ = 2.2 {Kappa} in GaBa/sub 2/Cu/sub 3/O/sub 6+{delta}/ with {delta} = 0.7. This was confirmed by a neutron scattering experiment. The compound also exhibits a superconducting transition at T/sub c/ = 94 {Kappa}, and, hence, superconductivity and antiferromagnetism coexit below T/sub N/. It is important to elucidate whether the occurrence of the two critical phenomena is consequential or just accidental. It has been demonstrated that 123 samples with low oxygen content are not superconducting. The study of a nonsuperconducting sample should provide some clues. Thus, the same calorimetric measurements were made on a second GdBa/sub 2/Cu/sub 3/O/sub 6t{delta}/ sample with further oxygen deficiency, {delta} = 0.5. The material is no more superconducting, but magnetic susceptibility studies show that there is still an anomaly at 2.2 {Kappa}. Heat capacity measurements were based on the standard adiabatic calorimetry with Joule heating and germanium thermometry. The results are shown.