Dynamical properties in metallic reentrant in spin glasses studied by inelastic neutron scattering

We have studied the temperature dependence of the magnetic collective excitations in two ferromagnetic reentrant systems (Fe1-xMnx)75P16B6Al3 and Cr1-xFex. The excitations are spin waves obeying the dispersion relation ω = Δ + Dq2, where D is the magnetic stiffness constant of the system. Our measurements, using inelastic neutrons scattering, evidenced large anomalies on the thermal evolution of the magnetic dynamics the concentration dependence of which is also reported. The concentration dependence determined on a-FeMn allows us to understand better the behaviour reported for other systems where less precise measurements lead to erroneous conclusions. This point of view has been corroborated by a reexamination of the CrFe, first compound of this kind which had been studied by inelastic neutron studies. Our observations allow an interesting check for mechanisms homogeneous or inhomogeneous, which may be put forward in these systems. Associated to the observations by elastic neutron scattering they provide a new material for theoretical models