Unconventional magnetic excitation in the Kondo lattice CeCu2

Abstract We have performed inelastic neutron scattering experiments on the Kondo lattice CeCu 2 ( T K = 6 K ) in the magnetically ordered state ( T N = 3.5 K ) at T ≈ 2 K in magnetic fields up to 12 T. The orthorhombic crystal structure and the simple antiferromagnetic structure require two magnon modes. In the induced ferromagnetic state, an additional magnetic excitation was detected. We suppose that a double π / 2 spin flop process is responsible for this unexpected excitation.