The effect of nuclear spin waves on the magnetization of MnCO₃

By means of a SQUID magnetometer the authors have investigated the change of magnetic moment Delta M caused by RF pumping at NMR frequency in the easy-plane antiferromagnet MnCO 3 . It is shown that Delta M arises mainly from a non-thermal packet of nuclear k=0 magnons. A characteristic time T 3 describing the relaxation of these magnons into the whole nuclear dispersion branch was evaluated from the experimental data. The authors found that T 3 is much smaller than the spin-lattice relaxation time T 1 , which means that the strongly excited nuclear system can be described by a separate spin temperature T n . A relaxation mechanism for T 3 is discussed which could explain the observed field and temperature dependences of Delta M.