Mössbauer effect study of face-centered-cubic-like Fe on Cu(001)

Abstract

Epitaxial face-centered-cubic (fcc)-like Fe films have been investigated in situ in ultrahigh vacuum by 57Fe conversion-electron Mössbauer spectroscopy (CEMS). A broad distribution of hyperfine magnetic fields, P(Bhf), with an extrapolated most-probable field of 32(2) T at magnetic saturation has been observed in ∼3 monolayers (ML) thick films grown at ∼90 or 300 K, and in ∼7 ML thick films grown at ∼90 K. Such films are in a ferromagnetic high-spin state. Their local structure is characterized by an electric quadrupole interaction, eQVZZ/4, of +0.114±0.05 mm/s from which we infer an anisotropically expanded fcc (fct-like) structure with c/a≊1.06. Approximately 5–7 ML thick films grown at 300 K are observed to be in a low-spin antiferromagnetic state below TN∼70 K, and are fcc (c/a=1) above TN. Site-selective CEM spectra taken on such films provide direct evidence for a magnetically ‘‘live’’ surface layer. The fcc→bcc transformation occurring in 35 ML thick films deposited at 300 K was observed to be incomplete.