Site-Dilution in quasi one-dimensional antiferromagnet Sr2(Cu1-xPdx)O3: reduction of Neel Temperature and spatial distribution of ordered moment sizes

We investigate the Neel temperature of Sr2CuO3 as a function of the site dilution at the Cu (S=1/2) sites with Pd (S=0), utilizing the muon spin relaxation (muSR) technique. The Neel temperature, which is Tn=5.4K for the undoped system, becomes significantly reduced for less than one percent of doping Pd, giving a support for the previous proposal for the good one-dimensionality. The Pd concentration dependence of the Neel temperature is compared with a recent theoretical study (S. Eggert, I. Affleck and M.D.P. Horton, Phys. Rev. Lett. 89, 47202 (2002)) of weakly coupled one-dimensional antiferromagnetic chains of S=1/2 spins, and a quantitative agreement is found. The inhomogeneity of the ordered moment sizes is characterized by the muSR time spectra. We propose a model that the ordered moment size recovers away from the dopant S=0 sites with a recovery length of \xi = 150-200 sites. The origin of the finite recovery length \xi for the gapless S=1/2 antiferromagnetic chain is compared to the estimate based on the effective staggered magnetic field from the neighboring chains.