Crystal distortion and the magnetic moment of epitaxially grown alpha ''-Fe16N2

The magnetic moment of alpha "-Fe16N2 has been explored for epitaxial Fe-N thin films grown on Fe and Ag(001) single-crystal underlayers. Clear eviden ces for multiple states which have strong correlation with the crystal stru cture of alpha "-Fe16N2 are obtained by the measurements of ferromagnetic r esonance, the phase transition temperature, and the lattice constants. The magnetic moment of the films was found to have a strong correlation with th e unit cell volume of alpha "-Fe16N2. The (alpha " + alpha')-Fe16N2 with a large unit cell volume around 205.8 Angstrom(3), which is equal to the valu e reported by Jack, exhibits very high average magnetic moment of about 2.8 mu(B)/Fe atom, and the moment increases with the degree of N site ordering . On the other hand, (alpha " + alpha')-Fe16N2 with a smaller unit cell vol ume of around 204 Angstrom(3) obviously Shows lower average magnetic moment of 2.5 mu(B)/Fe atom, and the moment is independent. It is highly possible that the large discrepancy of magnetic moment of alpha "-Fe16N2 reported s o far is due to the difference of unit cell volume of alpha "-Fe16N2, which sensitively depends on sample preparation conditions, him thickness and so on. The present study has also clarified the phase transformation process of alpha "-Fe16N2 to gamma'-Fe4N, and this process is well explained by the Usikov's model. (C) 2000 Published by Elsevier Science B.V. All rights res erved.