Magnetocrystalline anisotropy for α´-Fe-C and α´-Fe-N films

Structural and magnetic analyses were made for α´-Fe-C (0-12 at.%C) and α´-Fe-N(0-12 at.%N) films. The results are summarized as follows: (1) epitaxial Fe-C films consisting of an α´-Fe-C single phase with a C content up to 12 at.% can be synthesized on MgO single crystal substrates by sputtering. (2) The change in lattice constants, a and c, as a function of the C content for the α´-Fe-C phase was found to be the same as that of the α´-Fe-N against the N content. (3) The saturation magnetization for the α´-Fe-C films maintains a constant value of about 210 emu/g (≈2.1 T) up to 8 at.%C. (4) The easy axis of magnetization of α´-Fe-N corresponds to the c-axis of the bct structure. Even though the α´-Fe-C phase has the same bct structure as the α´-Fe-N, the easy axis of magnetization lies in the (001) plane, (5) the value of the uniaxial magnetocrystalline anisotropy, K, for α´-Fe-C is -2×10⁹ erg/cm³ independent of the C content, and the magnetocrystalline anisotropy constant, K₃ decreases with increasing C content and is about 3×10⁵ erg/cm³ at 12 at.%C. (6) the value of the coercive force for the α´-Fe-C films with C content more than 4 at.% is about 2 Oe. From this study, it is found that the α´-Fe-C films with 4-8 at.%C are promising candidates for use as writing head material