Phenomenological model of the magnetic properties of La_2-xSr_xCuO_4-y

Abstract

We model La_2-xSr_xCuO_4-y for small x by assuming p_π oxygen holes are Coulombically bound to Sr (or La vacancy) acceptor defects in 2d hydrogenic orbitals. The holes exchange couple to the antiferromagnetically ordered copper moments. The defects are polarized due to the copper spin canting induced by the Dzyaloshinski-Moriya interaction. Within linear spin-wave analysis we obtain a defect contribution to the magnetization jump at a critical applied field H_c, and we deduce a critical defect concentration for suppression of the long-range magnetic order which is sensitive to dimensionality, defect position, and defect-defect interactions. We quantitatively account for the nonmetal-metal transition. We qualitatively explain the observed resistivity drop at H_c (for which we propose an experimental test), some anomalous muon-spin-resonance data, and the dependence of T_N on oxygen vacancies.