Application of Mössbauer spectroscopy in magnetism

An overview is provided on our recent work that applies 57Fe Mössbauer spectroscopy to specific problems in nanomagnetism. 57Fe conversion electron Mössbauer spectroscopy (CEMS) in conjunction with the 57Fe probe layer technique as well as 57Fe nuclear resonant scattering (NRS) were employed for the study of various nanoscale layered systems: (i) metastable fct-Fe; a strongly enhanced hyperfine magnetic field Bhf of ∼39 T at 25 K was observed in ultrahigh vacuum (UHV) on uncoated three-monolayers thick epitaxial face-centered tetragonal (fct) 57Fe(110) ultrathin films grown by molecular-beam epitaxy (MBE) on vicinal Pd(110) substrates; this indicates the presence of enhanced Fe local moments, μFe, as predicted theoretically; (ii) Fe spin structure; by applying magnetic fields, the Fe spin structure during magnetization reversal in layered (Sm–Co)/Fe exchange spring magnets and in exchange-biased Fe/MnF2 bilayers was proven to be non-collinear and depth-dependent; (iii) ferromagnet/semiconductor interfaces for electrical spin injection; CEMS was used as a diagnostic tool for the investigation of magnetism at the buried interface of Fe electrical contacts on the clean surface of GaAs(001) and GaAs(001)-based spin light-emitting diodes (spin LED) with in-plane or out-of-plane Fe spin orientation; the measured rather large average hyperfine field of ∼27 T at 295 K and the distribution of hyperfine magnetic fields, P(Bhf), provide evidence for the absence of magnetically “dead” layers and the existence of relatively large Fe moments (μFe ∼ 1.8 μB) at the ferromagnet/semiconductor interface. - Finally, a short outlook is given for potential applications of Mössbauer spectroscopy on topical subjects of nanomagnetism/spintronics.