Antiferromagnetism ofLa2CuO4−ystudied by muon-spin rotation

Zero-field spin precession of positive muons has been observed in the antiferromagnetic state of ${\mathrm{La}}_2$ ${\mathrm{CuO}}_{4\mathrm{-}\mathrm{y}}$. Sharp onsets of the sublattice magnetization are found at temperatures close to those of the susceptibility maxima of different specimens. The long-lived precession signal indicates a microscopically homogeneous distribution of spin density at each Cu atom below the Néel temperature. Combination of the present results and neutron-scattering studies indicates the ordered moment per Cu atom to be significantly less than 1${\mathrm{\mu }}_{\mathrm{B}}$.