Sr impurity effects on the magnetic correlations of La 2-x Sr x CuO 4

We examine the low-temperature magnetic properties of moderately doped La{sub 2{minus}x}Sr{sub x}CuO{sub 4}, paying attention to the spin-glass phase and the commensurate-incommensurate transition as they are affected by Sr impurity disorder. A model of the carriers, believed to be appropriate at low temperatures, is employed in the CuO{sub 2} planes that accounts for both the strong coupling of the hole`s motion to the antiferromagnetically correlated spins and the pinning potential associated with the Sr impurities. This model has been shown to explain quantitatively several magnetic and transport features of the antiferromagnetic region of the phase diagram. Preliminary indications that this model also can explain the x{ge}0.02 region of the phase diagram follow from its success in accounting for the doping and temperature variation of the spin correlation length. Here we attempt to explain various features of the spin texture of the spin-glass phase. New measurements with traveling-solvent float zone grown crystals of the low-temperature susceptibility show an increase of an anomalously small Curie constant with doping. This behavior is modeled in terms of our numerical simulation results that find small clusters of antiferromagnetically aligned regions separated by disordered domain walls produced by the impurities {emdash} the domain walls lead tomore » a percolating sequence of paths connecting the impurities. We predict that for this spin morphology the Curie constant should scale as 1/[2{xi}(x,T=0){sup 2}], {xi} being the spin correlation length, quantitatively in agreement with experiment. We find that the magnetic correlations in the ground states produced by our simulations are commensurate in the spin-glass phase, consistent with experiment, and that this behavior will persist at higher temperatures where the holes should move along the domain walls effectively being expelled from the antiferromagnetically correlated domains. (Abstract Truncated)« less