UC Irvine

Zero-field La139 nuclear quadrupole resonance (NQR) has been used to characterize the antiferromagnetic transition in nearly stoichiometric single crystals of La2CuO4+ (Néel temperatures TN between 275 and 318 K). The onset of the NQR Zeeman splitting at TN is abrupt but continuous, indicative of a second-order phase transition with either a crossover in critical behavior just below TN or a very small critical exponent 0.1. The absence of any anomaly at TN in the La139 electric field gradient indicates no accompanying structural distortion. © 1994 The American Physical Society.