Observation of ferromagnetic spin waves in a "reentrant" Ni-Mn alloy

Neutron scattering measurements in a "reentrant" Ni-Mn alloy reveal well-defined spin waves at all temperatures below $T_c$ (330 K), particularly and for the first time, below $T_f$ (40 K) the temperature of the down turn in the ac susceptibility. The spin waves coexist with intense quasielastic scattering which develops below ∼100 K, and the spin-wave damping, the stiffness constant, and the transverse susceptibility are all enhanced. The results contradict the common hypothesis of a breakup of the infinite ferromagnetic network in the reentrant state at $T_f$.