Spin Dynamics in Itinerant Antiferromagnetic γFeMn Alloys

The spin wave excitations in the itinerant antiferromagnetics of γFeMn alloys have been studied by neutron scattering. The isotropic dispersion relation has been observed for γFe 0.7 Mn 0.3 and γFe 0.5 Mn 0.5 . The velocities of spin waves at room temperature are 230±30 meVA, 220±30 meVA and 160±30 meVA for Fe 0.7 Mn 0.3 , Fe 0.5 Mn 0.5 and Fe 0.3 Mn 0.7 , respectively. All samples have the spin wave energy gaps of about 10 meV at 0 K which shows a similar temperature dependence. The damping of the spin wave is significant and it depends on the momentum transfer of the spin waves. The magnon-like excitation persists even 200 degrees above the Néel temperature for Fe 0.5 Mn 0.5 . The results are favorable to the itinerant electron model where the multiple spin density wave state is assumed to exist.