Abstract
Mossbauer absorption measurements on the 84.25 keV gamma ray of 170Yb in YbAl3 have been made from 1.2K to 130K in applied magnetic fields up to 75 kOe. The isomer shift measurements show that Yb has a temperature independent valency of 2.7+or-0.3. An excess hyperfine field, induced by an applied magnetic field, is explained in terms of an ionic orbital hyperfine field generated by a strongly correlated 4f electron band.