The magnetic electron distribution in MnPt3 ferromagnetic alloy has been determined by the polarized neutron technique. The Mn form factor in the ferromagnetic state has been determined and agrees closely with the theoretical one calculated for the free atom. The magnetic moments are (3.64±0.08)jLtjj for Mn atoms and (0.26 ±0.03)^/3 for Pt atoms. The magnetic electron distribution on Pt atoms is strongly aspherical. The tetragonal field splits the d levels into sublevels. The population of these sublevels has been estimated.

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Spin-wave dispersion relations, in the momentum range 0.1 2 2 (l~/3g 2 -|-yg 4 ), the stiffness constant D has been found to be 273±3 and 233±11 meV A 2 , respectively, for the two alloys. Values of 3.7±0.2 and 4±2 A 2 were obtained for the parameter @. These values of /S, as well as the concentration dependence of the stiffness constants, appear to be inconsistent with a nearest-neighbor Heisenberg model.