169Tm Mössbaüer spectroscopy and crystal field calculations in TmNi3 and TmCo3 intermetallics

The values of the magnetic moments and the electric field gradient in TmNi₃ and TmCo₃ are obtained from ¹⁶⁹Tm Mössbauer spectroscopy. These values are compared to those from crystal field model based on point charge calculations for these intermetallics.     

57Fe Mössbauer study in the ternary hydrides of ErFe3

The ternary hydride phases ErFe₃Hx (with x=1.5 and 2.7) has been studied by⁵⁷Fe Mössbauer effect. The spectra show that the spin reorientation temperature is increased by the presence of hydrogen in the ErFe₃ lattice and is independent of hydrogen concentration for the two hydrides investigated. A preferential filling of the interstitial sites in the RFe₃ structure is indicated by the data.Work supported in part by Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) and Financiadora de Estudos e Projetos (FINEP).     

57Fe Mössbauer investigation of the ternary hydride Pd3FeHx

Ordered alloys of Pd₃Fe are shown to readily absorbe hydrogen through electrolytic loading. The resultant ternary hydride phase is observed to retain the fcc structure of Pd₃Fe with approximately the same lattice constant. The ⁵⁷Fe hyperfine field determined by Mössbauer spectroscopy is found to be 30% smaller in the hydride compared to Pd₃Fe. The reduction appears to be associated with a perturbation of the Pd moment by hydrogen. The results suggest the occupation of one type of interstitial site in the structure. The absence of the site in disordered Pd₃Fe would explain the much smaller hydrogen capacity observed for this alloy.     

Low temperature scanning force microscopy of the Si(111)-(7x7) surface

A low temperature scanning force microscope (SFM) operating in a dynamic mode in ultrahigh vacuum was used to study the Si(111)- (7x7) surface at 7.2 K. Not only the twelve adatoms but also the six rest atoms of the unit cell are clearly resolved for the first time with SFM. In addition, the first measurements of the short range chemical bonding forces above specific atomic sites are presented. The data are in good agreement with first principles computations and indicate that the nearest atoms in the tip and sample relax significantly when the tip is within a few A of the surface.