Mössbauer Effect Study of Magnetism and Structure of fcc-like Fe(001) Films on Cu(001)

Magnetic and electric hyperfine interactions observed in situ by conversion-electron Mössbauer spectroscopy in 3 and 7 monolayers thick Fe films grown epitaxially in UHV on Cu(001) at 300 K provide microscopic evidence for a thickness-dependent transition from a high-moment ferromagnetic state with an anisotropically expanded fcc (fct-like) structure $\left(c/a>\mathrm{}1\mathrm{}\right)$ to a low-moment antiferromagnetic isotropic fcc state. In similar films grown at $\sim 90$ K and annealed to 300 K, however, this high-moment fct-like phase was found to exist at both thicknesses. We conclude that the high-moment ferromagnetic state can exist in fct-like Fe only, but not in fcc Fe.