Ultrathin films (10 to 17 monolayers) of fcc Fe(100) grown epitaxially on Cu(100) are unambiguously found to be paramagnetic at 295 K by ${}_{}{}^{57}{}_{}{}^{}\mathrm{Fe}$ conversion-electron Mössbauer spectroscopy in UHV. Below $T_{\mathrm{N}}=65\mathrm{}\pm 5$ K, fcc-Fe films are magnetically ordered and show a small average hyperfine field, e.g., 1.1 T at 29 K for 10 monolayers, indicating a small atomic magnetic moment. This demonstrates that fcc Fe(100) stabilized at a lattice constant close to that of Cu has an antiferromagnetic ground state.

• Received 13 November 1987

DOI:https://doi.org/10.1103/PhysRevLett.61.475