ON THE MAGNETIC ORDER OF ULTRATHIN MN LAYERS ON FE(001)

Using an intra-atomic exchange integral J(Mn) as a fitting parameter i n a self-consistent tight-binding model calculation with 3d-orbitals o nly, we have studied the magnetic behaviour of ultrathin Mn films on F e(001) for parallel (P) and antiparallel (AP) coupling at the Fe/Mn in terface. For a single Mn monolayer on Fe(001) we find a sensitive depe ndence of the magnetic moment on J(Mn). In the AP case, there is a rat her sharp, but continuous transition from a low-spin state with mu(Mn) approximate to 0.4 mu(B) for J(Mn) < J(c) to a high-spin state with m u(Mn) approximate to 4 mu(B) for J(Mn) > J(c). The experimental value of similar to 2.9 mu(B) lies in the transition region of the energetic ally favoured P coupling which exists only in the high-spin state.