Low-temperature magnetism ofNd2CuO4: An ultrasonic investigation

Abstract

We have performed an ultrasonic study of ${\mathrm{Nd}}_{2}{\mathrm{CuO}}_{4}$ in order to investigate the low temperature magnetism due to the ${\mathrm{Nd}}^{3+}$ moments. In addition to small anomalies corresponding to the ${\mathrm{Cu}}^{2+}$ 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 ${\mathrm{Nd}}^{3+}\text{\ensuremath{-}}{\mathrm{Cu}}^{2+}$ and the ${\mathrm{Nd}}^{3+}\text{\ensuremath{-}}{\mathrm{Nd}}^{3+}$ 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 ${\mathrm{Nd}}^{3+}$ spins which occurs at critical field lower than the one associated with the ${\mathrm{Cu}}^{2+}$ spins.