Nuclear Magnetic Relaxation in the Ferrimagnetic Chain Compound   NiCu(C_7_H_6_N_2_O_6_)(H_2_O)_3_2H_2_O: Three-Magnon Scattering?
  Recent proton spin-lattice relaxation-time (T_1_) measurements on the ferrimagnetic chain compound NiCu(C_7_H_6_N_2_O_6_)(H_2_O)_3_2H_2_O are explained by an elaborately modified spin-wave theory. We give a strong evidence of the major contribution to 1/T_1_ being made by the three-magnon scattering rather than the Raman one. 
Hiromitsu Hori and Shoji Yamamoto