The spin wave dispersion of NdCu2 in strong magnetic fields

The study of the spin wave excitation spectrum in NdCu2 revealed a pronounc ed minimum which forms an energy gap. Previous experiments showed that the gap energy remains finite in external magnetic fields parallel to the b-axi s. In this paper we report on measurements of the spin wave dispersion in s trong magnetic fields applied parallel to the c-direction (hard magnetizati on axis). The spin wave gap changes its position and soft mode behavior at a magnetic phase transition is observed. The comparison with the dispersion at mu(0)H(11b) = 3 T reveals the anisotropy between (ac)-plane and h-axis. (C) 2000 Elsevier Science B.V. All rights reserved.