Non-exponential behavior of the nuclear magnetization in H-doped copper oxides.

Measurement of the spin lattice relaxation time in H-doped Y2BaCuO5 and YBa2Cu3O6 has revealed a power law growth of the nuclear magnetization M for short times following a saturation pulse sequence. Preliminary experimental results yield exponents of 1/2 and 1/3, depending on the amount of hydrogen present in the sample. We extend Blumberg's theory for relaxation due to paramagnetic centers via dipole-dipole interaction in the absence of spin diffusion to obtain M approximately tD/6 where D is the dimensionality of the system. This yields exponents of 1/2 and 1/3 for three- and two-dimensional systems, respectively. At long times the magnetization growth becomes exponential.