Statics and Dynamics of the Surface of AN Epitaxial Iron Film.

The temperature dependence of the magnetization at the surface of effectively semi-infinite epitaxial {110} iron samples was determined by Mossbauer spectroscopy. The Fe films, grown on epitaxial {111} Ag in ultra-high vacuum by vapor deposition, consisted of 30-70 atomic layers of isotopically pure ^ {56}Fe--except for the last two or three atomic layers, which were grown from the Mossbauer isotope ^{57}Fe. Covering each film was a thick layer of one of several non-diffusing, non-alloying, chemically non-interacting materials (Ag, MgO, MnF_2, MgF_2 ); these non-magnetic substances (except MnF _2, a weak antiferromagnet at low temperatures) exhibited different interactions with the moment and charge density at the Fe interface. The hyperfine field H_{rm HF} at the probe layer of each interface was measured at temperatures ranging from 4.2 K to 296 K. The Fe-Ag and Fe-MgO interfaces exhibited Bloch T^ {3/2} Law behavior, with a B factor of 3.4B_{rm Bulk} and 2.1B_{rm Bulk}, respectively. Also, the Fe-Ag interface showed a 3% increase of H_{rm HF} over bulk at 4.2 K, and a decrease of H_{ rm HF} at room temperature; while the Fe-MgO interface had H_{rm HF } decreased 3% from bulk at 4.2 K, and a comparable decrease at 296 K. The Fe-MnF_2 interface showed that H_{rm HF } increased greatly from bulk at all temperatures (7.6% at 4 K), as well as a definite quasilinear temperature dependence. The experiments show that our results are in accordance with recent theoretical calculations relating surface magnetization to H_{rm HF} and to the ionicity (or lack of it) of the covering material. The temperature dependence of each interface is explained using the semiclassical treatment of Rado. Evidence is also presented to confirm the localization of surface interactions near the interface.