The influence of interfacial interdiffusion on the magnetic order in ultrat
hin epitaxial Cr films on a Fe(001) substrate was studied by means of elect
ronic structure calculations. The total coverage of the films was assumed t
o be one, two, and six monolayers of Cr while the interdiffusion was simula
ted by two-dimensional Cr-Fe alloys in the two atomic layers forming the Cr
/Fe interface. Two limiting cases were considered: (i) perfectly ordered al
loys, described in terms of a semiempirical tight-binding method using the
recursion technique, and (ii) substitutionally disordered alloys, whose ele
ctronic structure was determined ab initio using the tight-binding linear m
uffin-tin orbital method and the coherent-potential approximation. In both
cases, the magnetic coupling of the Cr overlayer to the ferromagnetic Fe su
bstrate exhibits similar transitions (pi phase shifts) due to varying compo
sitions at the interface. The calculated results provide additional support
for recent interpretations of experiments on Fe/Cr/Fe(001) trilayers.