Low-temperature magnetism of Nd2CuO4:: An ultrasonic investigation -: art. no. 144425

We have performed an ultrasonic study of Nd2CuO4 in order to investigate the low temperature magnetism due to the Nd3+ moments. In addition to small anomalies corresponding to the Cu2+ spin reorientations observed at 33 and 67 K, a large magnetic field and frequency dependent anomaly is detected around 4 K in the C-66 elastic constant and the corresponding attenuation variations. The frequency dependence of this anomaly, which disappears under a magnetic field of 2 T applied along the in-plane Cu-O bonds, is related to a resonant phenomenon rather than to a phase transition as previously reported. The ultrasonic measurements suggest the development of local domains, due to a frustration of the magnetic structure caused by the competition between the Nd3+-Cu2+ and the Nd3+-Nd3+ interactions at low temperature. In contrast to the common belief, the C-66 elastic constant and attenuation anomalies above 2 T characterize a field-induced transition of the Nd3+ spins which occurs at critical field lower than the one associated with the Cu2+ spins.