We used polarized neutron reflectometry (PNR) to investigate the depth-dependent saturation magnetization (4πMs) of bi-layer structured Fe-N/Fe grown on MgO substrates, which were prepared by a facing target sputtering method followed by a subsequent annealing process to purposely study the N inter-diffusive effect. It is observed that by tuning the Fe layer thickness from 2 nm to 5 nm, the magnetic properties of the resulting product varies substantially. According to X-ray diffraction, an additional peak, indexed to Fe16N2 (004), was developed in the sample with thinner (2 nm) underlayer. Its corresponding PNR study shows a 4πMs of up to 2.82 T towards the substrate interface, which is 14% higher than the known limit (Fe65Co35 ∼ 4πMs = 2.45 T). We attribute this giant magnetization to the presence of chemically ordered Fe1N2. We have seen evidence that the high Ms is favorably stabilized due to the lattice misfit. The thickness range is consistent with the strained region of the films. This depth-dependent saturation magnetization analysis can shed a light to help understand the previous magnetization reports by classical magnetometry methods for the samples prepared using the same underlayer.
- facing target sputtering
- giant saturation magnetization
- iron nitride
- polarized neutron reflectometry