Similar glassy features in the 139La NMR response of pure and disordered La1.88Sr0.12CuO4

High T-c superconductivity in La2-xSrxCuO4 coexists with (striped and glassy) magnetic order. Here, we report NMR measurements of the La-139 spin-lattice relaxation, which displays a stretched-exponential time dependence, in both pure and disordered x=0.12 single crystals. An analysis in terms of a distribution of relaxation rates T-139(1)-1 indicates that: (i) the spin-freezing temperature is spatially inhomogeneous with an onset at T-g(onset)=20 K for the pristine samples and (ii) the width of the T-1(-1) distribution in the vicinity of T-g(onset) is insensitive to an similar to 1% level of atomic disorder in CuO2 planes. This suggests that the stretched-exponential La-139 relaxation, considered as a manifestation of the system's glassiness, may not arise from quenched disorder.