High-temperature spin dynamics of a cubic ferromagnetPd2MnSn

The paramagnetic scattering function S(q,ω) of the metallic ferromagnet ${\mathrm{Pd}}_2$MnSn has been investigated up to 4$T_C$ over a wide q range along the [100], [011], and [111] directions by means of both polarized and unpolarized neutron scattering techniques. The temperature and q dependence of the static response, $k_B$Tχ(q), is explained rather well by the Heisenberg model with long-range interactions, although there are nontrivial deviations from the theory. The features of the dynamical response are summarized as follows: (i) The scattering function has a simple one-peak form centered at ħω=0 in the whole q range at 1.5$T_C$ and 4$T_C$. (ii) The linewidths of the function near zone boundaries agree well with the calculations based on the three-pole approximation of the Heisenberg model. (iii) The linewidths near q=0 show the anomalously large temperature dependence, and have no $q^2$ dependence at 4$T_C$. These facts point to the importance of the nonadiabatic effects of the conduction electrons at high temperatures, even though the Heisenberg-type interactions between localized spins play the major role on the spin dynamics in this system.