PHASE-SEPARATION KINETICS IN LA2CUO4-LESS-THAN-X-LESS-THAN-0.02) OF LA2-XSRXCUO4(DELTA AND INHOMOGENEOUS HOLE DOPING IN THE ANTIFERROMAGNETIC REGIME(0)

The diffusion of the excess oxygen during phase separation in La2CuO4delta was studied using thermal history-dependent normal state magneti c susceptibility chi(T, t) measurements versus temperature T and time t as a probe. A large thermal hysteresis of chi(T) was observed for La 2CuO4.044 between data obtained after quenching to 5 K and then warmin g, and data obtained while or after slowly cooling from 300 K. A model for the excess oxygen diffusion is presented, from which the chi(T, t ) data yield a T-independent activation energy of 0.24(3) eV for the d iffusion coefficient of the excess oxygen from 150 to 220 K. In relate d work, we have used La-139 NQR and mu SR measurements to probe the an tiferromagnetic (AF) region (x < 0.02) of the La2-xSrxCuO4 system belo w the Neel temperature T-N(x), from which we extract the Cu+2 staggere d magnetization M(dagger)(x, T). M(dagger)(x, T = 0), extrapolated fro m above 30 K, was successfully modeled with spin-wave theory, assuming that the doped holes are mobile and are situated in walls in the CuO2 plane which uncouple undoped AF domains; these domains are coupled to those in adjacent CuO2 planes. This agreement supports the previous h ypothesis that microsegregation of the (mobile) doped holes into domai n walls occurs above similar to 30 K, consistent with the phenomenolog y of Emery and Kivelson. Below similar to 30 K, an anomalous increase in M(dagger)(x, T) is observed, such that M(dagger)(x, T = 0) is nearl y independent of x. We interpret this effect as arising from localizat ion of the doped holes below similar to 30 K.