Antisymmetric exchange and its influence on the magnetic structure and conductivity ofLa2CuO4

Measurements of the magnetic moment of antiferromagnetic ${\mathrm{La}}_2$Cu${\mathrm{O}}_4$ at high fields reveal a new phase boundary originating from a previously undetected canting of the ${\mathrm{Cu}}^{2+}$ spins out of the Cu${\mathrm{O}}_2$ planes. This canting, together with the exponential temperature dependence of the two-dimensional correlation length, accounts quantitatively for the susceptibility peak at the Néel temperature. Enhancement of the conductivity in the ferromagnetic phase demonstrates a strong connection between the magnetism and charge transport.