Abstract:
We have grown ultrathin CoₓNi₁₋ₓ and FeₓNi₁₋ₓ films on Cu(100) with varying stochiometry x. We find
that these alloy films grow in a fcc phase on Cu(100). With the surface magneto-optic Kerr effect we measured
the variation of the Curie temperature T_c as a function of the film thickness n in monolayers. Fitting an
empirical scaling curve to our results we are able to extrapolate the value T_c(n=[infinity])for samples with different
stochiometry. We use this framework in order to determine T_c(n=[infinity]) for FeₓNi₁₋ₓ alloy films, in particular
for concentrations close to 65% Fe content. Bulk Fe₆₅Ni₃₅ shows a collapse of magnetic long-range order and
a fcc-to-bcc structural transition, which is the so-called Invar effect. In ultrathin Fe₆₅Ni₃₅ films, we observe a
‘‘quenching’’ of the Invar effect, because growth on a Cu(100) substrate forces the film to adopt the Cu lattice
spacing thereby suppressing the structural relaxation.
