Single trilayer spin valves consisting of uncapped FeNi(60 angstrom)/C
u(60 angstrom)/Co(40 angstrom) have been grown using ultrahigh vacuum
(UHV) electron beam evaporation methods. Room temperature magnetoresis
tance (MR) measurements exhibit well defined plateaux corresponding to
the full antiparallel alignment of the FeNi and Co magnetizations. Th
is sharp switching behavior and precisely defined antiferrimagnetic st
ate is in contrast with the corresponding behavior reported for FeNi/C
u/Co multilayers.