Hyperfine interactions in amorphous Tm-Cu Alloys

Hyperfine interactions in sputtered amorphous Tm_xCu_1?x, with x=0.70, 0.50, and 0.33, have been measured over a temperature range from 1.7 K to room temperature using the Mössbauer effect in¹⁶⁹Tm. At low temperatures each spectrum shows a well resolved six-line hyperfine pattern indicative of magnetic order and a superimposed quadrupole doublet. The relative spectral weight of the magnetic component increases with increasing Tm concentration and decreases with increasing temperature. The magnetic component persists at unexpectedly high, temperatures with no decrease in overall splitting and no evidence of electronic relaxation. For all three concentrations, the magnetic splitting is the same as that of Tm metal at low temperatures, nearly the free-ion limit. The electric quadrupole shift of the magnetic component is the same for the three samples, but is significantly less than that of Tm metal (hexagonal) and much larger than that of crystalline TmCu (cubic). The non-magnetic doublets have quadrupole splittings that are very nearly the same for the three concentrations and show considerable asymmetry, a typical effect of electronic relaxation, which persists at temperatures above where the magnetic component disappears.