Magnetic moment distribution in NiMn alloys

Polarized-neutron diffuse-scattering measurements were made on Ni-rich NiMn alloys to determine the distribution of magnetic moments in this system. At 5-at.% Mn, the individual moments are (3.50 ± 0.13)${\mathrm{\mu }}_{\mathit{B}}$/Mn and (0.584 ± 0.013)${\mathrm{\mu }}_{\mathit{B}}$/Ni assuming no conduction-electron polarization. Both moments decrease with increasing Mn content and attain values of (1.10 ± 0.04)${\mathrm{\mu }}_{\mathit{B}}$/Mn and (0.300 ± 0.013)${\mathrm{\mu }}_{\mathit{B}}$/Ni at 20-at.% Mn. Near-neighbor magnetic-moment correlations appear in the scattering functions simultaneously with the decrease in moments, and, since the cross sections are dominated by the Mn contribution, this indicates that the ferromagnetically aligned Mn moment is strongly dependent on near-neighbor environment. The actual moment dependence on environment was not determined but this is not simply a matter of the number of Mn nearest neighbors as has been assumed in previously proposed competing interaction models. The Mn and Ni moments exhibit different relative magnetization behavior with a stronger temperature dependence for the Mn moment. This behavior is consistent with the quasi-independent local-moment model with an impurity-host to host-host coupling ratio of about 0.3.