Study of the spin dynamics in invars by small angle polarised neutron scattering
Abstract
The spinwave dynamics in partially ordered Fe_{75}Pt_{25} and disordered Fe_{65}Ni_{35} invar alloys are investigated in the subcritical and intermediate temperature ranges using the inclined geometry method (IGM) in small angle polarised neutron scattering (SAPNS). This method is based on the analysis of the leftright asymmetry in the magnetic inelastic SAPNS arising when the direction of the magnetisation in the sample is inclined to the incident neutron wave vector. The spinwave (SW) parameters, such as the SW stiffness D and the SW damping Γ, are obtained by comparison of the antisymmetrical contribution to the scattering with a model function. The temperature behaviour of the SW stiffness D was fitted using expression: D~τ^{x}, where τ=1T/T_{C}. It was found that x=0.48+/0.01 and x=0.58+/0.05 for the range τ>0.1 for FeNi and FePt systems, respectively. The temperature behaviour of SW parameters D and Γ breaks down near T_{C} in the range τ<0.1. Hence, we observe a crossover from meanfield theory predicting x=0.5 to critical dynamics.
 Publication:

Physica B Condensed Matter
 Pub Date:
 July 2004
 DOI:
 10.1016/j.physb.2004.03.078
 Bibcode:
 2004PhyB..350E.319M
 Keywords:

 Spin wave;
 Invar