Magnetic field dependence of Nd 3+ spin waves in Nd 2CuO 4

Abstract

Low-energy spin waves in Nd 2CuO 4 at very low temperatures are due to transitions within the ground-state doublet of Nd 3+. The spin structure is noncollinear AF in zero field and transforms into a collinear AF structure at a magnetic field of H 1 = 0.7 T applied parallel to the crystallographic 1 1 0-direction. We present a study of the field dependence of the Γ-point mode at Q = (0 0 2) at T = 0.5 K with H|| [1 1 0] . A single excitation at E = 0.4 meV was observed field. At an intermediate field of about H = 2 T, a weak peak at a lower energy appeared which increases its intensity linearly while the first peak decreases with increasing field. The appearance of the new mode coincides with an anomaly of the linear dependence of the intensity of the (0.5, 0.5, 4) magnetic Bragg reflection with applied field. Above a critical field of about 4 T a splitting into dispersive modes takes place.