Two-dimensional antiferromagnetic excitations in Nd 2CuO 4

Inelastic neutron scattering experiments have been carried out on a Nd ₂CuO ₄ single crystal to investigate the magnetic excitations spectrum arising from the Cu ²⁺ spins. The fluctuations of the out-of-plane spin component exhibit an anisotropy gap of about 5.5 meV. The fluctuations of the in-plane spin component seem to present also a gap which is only sizeable in phase II.