Electron paramagnetic resonance (EPR) from ${\mathrm{Cu}}^{2+}$ ions is observed at very high temperatures in the tetragonally distorted perovskite ${\mathrm{LaCuO}}_{3\mathrm{-}\mathrm{\delta }}$, where for small δ most of the copper ions are presumably in trivalent states. Upon lowering the temperature, linewidths rapidly increase and the spectra are shifted to lower fields. The temperature dependence of the EPR linewidth is similar to what has been predicted, but not yet observed, for high-temperature superconductors and related antiferromagnets. A nonzero but small magnetization at low temperatures and low magnetic fields points to a canted magnetism due to strong long-ranged antisymmetric exchange interactions between randomly distributed ${\mathrm{Cu}}^{2+}$ ions in a matrix of ${\mathrm{Cu}}^{3+}$ Van Vleck ions.

• Received 17 December 1990

DOI:https://doi.org/10.1103/PhysRevB.43.11411