Exchange interaction studies using epitaxially stabilized expanded fct-Mn(0 0 1)

It is demonstrated experimentally that expanded face centred tetragonal (e-fct) Mn, which is characterized by an axial ratio c/a > 1, can be stabilized by epitaxial growth on ferromagnetic (FM) fct Co(0 0 1) films. At room temperature this new metastable Mn phase is antiferromagnetically (AFM) ordered for thicknesses above the 2.5 monolayer, as inferred from AFM/FM magnetic exchange interaction studies. This critical thickness does not depend on the magnetization direction of the FM layer. Even though for out-of-plane magnetized FM layers the coercivities are distinctly enhanced by the exchange interaction, no exchange bias can be detected. On the other hand, both coercivity enhancement and exchange biasing is observed for the in-plane magnetized FM/e-fct Mn bilayer. These results provide experimental evidence that the AFM spin structure of e-fct Mn at the AFM/FM interface is confined to the film plane