Anomalous spin-wave behavior in the magnetic alloyFexCr1−x

Neutron scattering methods are employed to study the temperature and magnetic field dependence of the spin dynamics in the alloy ${\mathrm{Fe}}_x{\mathrm{Cr}}_{1-x}$ for $x=0.34,0.28,0.26,0.24, \mathrm{and} 0.22$. For $x=0.34\mathrm{} \mathrm{and} 0.28$, the system orders ferromagnetically and exhibits well-defined spin waves throughout the ferromagnetic phase. For $x<~0.26$, ferromagnetism is also present but at low temperatures a spin-glass-like phase exists. For these concentrations the spin-wave excitations are observed within the ferromagnetic phase but as the temperature is lowered towards the spin-glass regime the spin-wave frequency decreases. At low temperatures, within the spin-glass regime, no well-defined excitations are present, but an intense quasielastic peak is observed. Application of a magnetic field causes a reemergence of the spin-wave excitations.