LOW-ENERGY EXCITATION IN THE INFINITE-LAYER ANTIFERROMAGNET CA0.85SR0.15CUO2

We report a Cu-63,Cu-65 NMR spin-lattice and transverse relaxation stu dy in the infinite-layer antiferromagnet Ca0.85Sr0.15CuO2. Experiments were performed in the antiferromagnetic phase between 5.4 and 504 K u sing two samples of different hole concentration. Despite their low co ncentration of about 10(-4), the holes strongly affect both relaxation types. At T< 100 K, a maximum in the spin-lattice relaxation rate has been quantitatively described considering the effect of holes diffusi ng with an activation energy of 27 meV which is independent from the c oncentration. The transverse relaxation is mainly induced by spin-spin indirect coupling. Its strong doping dependence can be directly relat ed to a strong doping dependence of the electronic susceptibility at z ero frequency and at the antiferromagnetic wave vector. [S0163-1829(98 )08029-1].