Polarized-neutron-diffraction study of the microscopic magnetic structure in α-Fe16N2 nanoparticles

Polarized-neutron-diffraction (PND) measurements were carried out using a pseudo-single-phase powder sample of ferromagnetic alpha ''-Fe16N2 nanoparticles. For the well-identified alpha ''-Fe16N2 phase, sizes of the magnetic moments at the three crystallographic Fe sites were determined in the absolute scale. The agreement between the magnetization value deduced from the present PND and that measured by a magnetometer (M-VSM) supports the hypothesis that M-VSM is primarily caused by the magnetization value in the target alpha ''-Fe16N2; thus there is no evidence for macroscopic giant saturation magnetization, at least for alpha ''-Fe16N2 nanoparticles. On the basis of the large magnetic moment size at one of the Fe sites, a possible coexisting state of localized spins and itinerant electron spins is inferred. Drawing a distinction between thin films and nanoparticles is currently necessary because of their divergent magnetic evolutions.