Magnetic structure of Fe16N2 determined by polarized neutron diffraction on thin-film samples

Abstract

Strain-free ${\mathrm{Fe}}_{16}{\mathrm{N}}_{2}$ thin films were obtained on MgO (001) single-crystal substrates with Cr seed layers. X-ray diffraction and transmission electron microscopy confirmed that the film is textured in all three spatial directions with crystallographic orientation determined by epitaxial constraints from the substrate. Average grain size was estimated to be in the range of tens of nanometers. Ten pieces of 40-nm-thick ${\mathrm{Fe}}_{16}{\mathrm{N}}_{2}$ thin-film samples were stacked together for half-polarized neutron diffraction study at room temperature. A total of six reflections were usable, from which the magnetic structure of ${\mathrm{Fe}}_{16}{\mathrm{N}}_{2}$ was determined and compared to existing models. Contrary to most electronic structure calculations, the present results suggest that the magnetic moment of Fe atoms at the $8h$ site is large and larger than that of the $4d$ site. Our results support the giant magnetization of ${\mathrm{Fe}}_{16}{\mathrm{N}}_{2}$.