Confirmation of antiferromagnetism inLa2CuO4−ywith polarized neutrons

We have used neutron polarization analysis to study the superlattice peaks observed recently in undoped ${\mathrm{La}}_2$ ${\mathrm{CuO}}_{4\mathrm{-}\mathrm{y}}$ using unpolarized powder neutron diffraction. The results confirm that the superlattice peaks are indeed due to antiferromagnetic ordering, which occurs for our sample below $T_N$=290±30 K, in agreement with our magnetic susceptibility data which yield $T_N$=290±10 K. The low-temperature moment on the Cu ion is estimated as 0.43±0.13${\mu }_B$ in agreement with the previous estimates.