SR IMPURITY EFFECTS ON THE MAGNETIC CORRELATIONS OF LA2-XSRXCUO4

We examine the low-temperature magnetic properties of moderately doped La2-xSrxCuO4, paying particular 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 appropriat e at low temperatures, is employed in the CuO2 planes that accounts fo r both the strong coupling of the hole's motion to the antiferromagnet ically correlated spins and the pinning potential associated with the Sr impurities. This model has been shown to explain quantitatively sev eral magnetic and transport features of the antiferromagnetic region o f the phase diagram. Preliminary indications that this model also can explain the x greater than or equal to 0.02 region of the phase diagra m follow from its success in accounting far the doping and temperature variation of the spin correlation length. Here we further scrutinize this model by attempting to explain various features of the spin textu re of the spin-glass phase. New measurements with traveling-solvent fl oat zone grown crystals of the low-temperature susceptibility show an increase of an anomalously small Curie constant with doping. This beha vior 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 - the domain walls lead to 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)(2)], xi being the spin correlation length, a result that is quantitatively in agreement with experiment. Also, we find th at the magnetic correlations in the ground states produced by our simu lations are commensurate in the spin-glass phase, consistent with expe riment, and that this behavior will persist at higher temperatures whe re the holes should move along the domain walls effectively being expe lled from the antiferromagnetically correlated domains. However, our r esults show that incommensurate correlations develop continuously arou nd 5% doping with an incommensurate wave vector along [(+/- 1,0),(0,+/ - 1)], consistent with recent measurements by Yamada et al. At this do ping lever the domain walls and not the clusters start to become the d ominant feature of the spin texture, and thus the Curie behavior shoul d disappear in the incommensurate phase, again consistent with experim ent. Thus, we find that this model is capable of describing the low-te mperature disorder-induced magnetic spin morphologies of the La2-xSrxC uO4 system in the low and intermediate doping regions of the phase dia gram. Coupling this understanding of the magnetic correlations with th e observed transport features, it is clear that impurity effects stron gly influence the physics of LaSrCuO.