Direct Evidence for Perpendicular Spin Orientations and Enhanced Hyperfine Fields in Ultrathin Fe(100) Films on Ag(100)

Abstract

Conversion-electron M\"ossbauer measurements have been used to study hyperfine fields in Fe/Ag(100) single-crystal multilayer films at temperatures down to 15 K. The Fe layer thicknesses corresponded to 1.0, 2.4, and 5.5 monolayers (ML). From the relative intensity of the M\"ossbauer lines we show conclusively that the orientation of the magnetic moment of the 1.0- and 2.4-ML films in zero applied field is perpendicular to the film plane while the orientation of the 5.5-ML sample is in plane at room temperature and partially out of plane at low temperatures. The low-temperature hyperfine fields are enhanced compared to bulk Fe.