Single-phase, single-crystal Fe16N2(001) films and Fe-11 at. %N martensite films of 200-900 Å thickness have been epitaxially grown on In0.2Ga0.8As(001) substrates by evaporating Fe in an atmosphere of mixed gas of N2 and NH3, followed by annealing. The saturation magnetizations 4πMs's for Fe 16N2 and Fe-N martensite films have been measured to be around 29 and 24 kG at room temperature, respectively, and almost constant in the above thickness range by using a vibrating sample magnetometer. 4πM s for Fe-N martensite films has been increased with ordering of N atoms caused by annealing and finally reached around 29 kG for Fe 16N2. Mössbauer spectra have been measured for those films. The spectrum for Fe-N martensite films was a superposed one with hyperfine fields of 360, 310, and 250 kOe, similar to those previously reported for martensite. While the spectrum became simpler with ordering, finally reaching a single hyperfine field of 330 kOe for Fe16N2. 4πMs of 29 kG for Fe16N2 (3.2 μB/Fe atom) and 4πMs of 24 kG for martensite (2.6 μB/Fe atom) has not been explained based on the conventional band theory of 3d metal magnetism. Behaviors of Mössbauer spectra could not be understood based on the conventional concept either. Thus a new physical concept is likely to be needed for clarification of giant magnetic moments and Mössbauer spectra for Fe16N2 and Fe-N martensites.
ASJC Scopus subject areas
- Physics and Astronomy(all)