MAGNETIC AND PHYSICAL MICROSTRUCTURE OF FE16N2 FILMS GROWN EPITAXIALLY ON SI(001)

Epitaxial Fe16N2 films were grown on Si(001) substrates with an Ag und erlayer by reactive sputtering in nitrogen. Pure alpha'-Fe8N films wer e obtained which on subsequent annealing resulted in mixtures of alpha '-Fe8N (54%) and alpha ''-Fe16N2 (46%). An average moment of 1780 emu/ cc, considerably larger than that of pure alpha-Fe (1714 emu/cc), was measured for both samples. Plan-view transmission electron microscopy of the films confirms the orientation relationship Fe16N2(001)parallel to Ag(001)parallel to Si(001) and Fe16N2[100]parallel to Ag[110]paral lel to Si[100], and a small grain size (similar to 100 Angstrom), whil e electron energy-loss spectroscopy confirms an average composition of Fe8N for both samples. Electron diffraction patterns indicate that th e as-deposited alpha' films already contain very small regions of orde red alpha '' which were not previously detected by x-ray diffraction m easurements. Mossbauer spectroscopy performed at both 300 and 16 K gav e three hyperfine fields corresponding to three different iron sites f or both the unannealed alpha' and the annealed alpha'/alpha '' mixture s. Lorentzian fitting of the three iron components for the alpha'/alph a '' spectrum obtained at room temperature gave an intensity ratio of 1:2:1 (FeI:FeII:FeIII) corresponding to the expected occupancy for the three Fe sites in the Fe16N2 structure. Moreover, the pure alpha' fil m at 300 K and both samples at 16 K showed deviation from this distrib ution. The three components show notable differences in the temperatur e dependence of their occupancies; however, all three magnetic compone nts deviate similarly from the surface normal. (C) 1997 American Insti tute of Physics.