Polarized neutron study of ferromagnetic Ni-Cu alloys: Evidence for a magnetic environment effect

Abstract

We measured the magnetic diffuse scattering of polarized neutrons from ferromagnetic Ni-Cu alloys with 19.8-, 29.6-, and 52.5-at.% Cu at 4.2 K. The data show that the Cu atoms are not polarized and that the negative polarization exists only around the Ni sites. Assuming that the Ni moments are a function of the moments of the neighboring atoms, we obtain an analytical expression for the polarized neutron cross section which describes the data well. This magnetic environment model is also shown to reproduce the moment disturbances of other dilute Ni based alloys. A Stoner type of calculation shows that between 20% and 40% interatomic exchange is needed to reproduce the Ni-Cu magnetization and cross sections; within the same calculation each Cu atom induces a (1-2)% moment reduction on its Ni neighbors for any given exchange field.