DIRECT EVIDENCE FOR INTERFACE-INDUCED PERPENDICULAR SPIN ORIENTATION AND SPIN REORIENTATION IN TERBIUM-COATED THIN IRON FILMS

Conversion-electron Mossbauer spectroscopy in ultrahigh vacuum has bee n employed to study in situ the average Fe-spin orientation and hyperf ine fields in zero external field in uncoated and Tb-coated Fe-57 film s deposited either onto a clean Tb(0001) single-crystal surface or ont o (bulklike) polycrystalline Th or Ag films. At 30 K, the spectra of 1 5-angstrom-thick uncoated Fe films on Tb(0001) indicate structurally d isordered (amorphous) Fe layers, whereas spectra of 30- or 35-angstrom -thick uncoated and coated Fe films are typical for bcc Fe. We show th at the orientation of Fe spins in 30-35-angstrom-thick uncoated Fe fil ms is preferentially in the film plane for temperatures ranging from 3 0-300 K for all substrates used. In striking contrast to uncoated film s Tb-coated 30-35-angstrom-thick Fe films exhibit a preferential Fe-sp in orientation perpendicular to the film plane at approximately 30 K i rrespective of the substrates used. This demonstrates (i) that the per pendicular spin orientation in these films originates from an interfac e magnetic anisotropy and (ii) that the dominant effect in inducing pe rpendicular spin direction originates from the interface formed by the Th-coating layer and the Fe film and to a smaller exent to the Fe/Tb- substrate interface. A temperature-dependent reversible Fe-spin reorie ntation was observed near 150-200 K which is qualitatively compatible with recent models including spin fluctuations.