Inelastic neutron study in superconductivity YBa2(Cu1-xCox)3O7

We have performed an inelastic neutron study in superconducting YBa2(Cu1-xCox)3O7, x=0.06, Tc=60K. At room temperature, the magnetic moment value M ≅3μB is close to the value determined by susceptibility measurements (3.4 μB). With decreasing temperature and approaching the superconducting transition, the magnetic intensity shows an anomalous increase. Finally, a spin glass like freezing is observed below a very high temperature (Tg=50K). These results are compared with those obtained in Fe-doped compounds and in Co-doped non superconducting compounds. YBa2(Cu1-xCox)3O7 has been widely studied by susceptibility measurements, X-ray and neutron diffraction. Like the Fe substitution, Co doping induces a decrease of Tc which vanishes for x>0.14 and an orthorhombic to tetragonal transition for x>0.3 [1]. We report here an inelastic neutron study of a superconducting sample with x=0.06. For this concentration. Co is found to occupy only the Cu1 site [2]. This differs from the Fe case where Moessbauer experiments have shown that 10% of the Fe atoms substitute on the Cu2 site [3]. 7 refs.; 2 figs