The paramagnetic state of BCC iron

Abstract

Calculations are reported of the static and dynamic properties of an effective Heisenberg model of Fe with exchange interactions extending to fifth-nearest neighbours. Exchange parameters chosen to fit the spin wave dispersion curve at room temperature lead to little short-range order above T_c and to a neutron scattering function S(q, ω) which is compatible with Lynn's 'constant ω ' plots. The dispersion curve obtained by plotting the positions of peaks in 'constant ω ' plots is in excellent agreement with the observed one but it does not correspond to propagating spin waves above T_c. The authors' results do not, however, reproduce the observed rapid drop of intensity at low frequency in 'constant q' scans.