Invar behavior of fccFe1−xNixthin films

From measurements of the thermal expansion and magnetization on uhv evaporated fcc Fe-Ni alloy films we show that the deviation of the average magnetic moment from the Slater-Pauling curve, observed in Fe-Ni bulk alloys around ${\mathrm{Fe}}_{65}$ ${\mathrm{Ni}}_{35}$, is not a necessary condition for the occurrence of the Invar effect. The results also address the long-debated issue of why in bulk Invar alloys the spin-wave stiffness is high when determined by inelastic neutron scattering, but low when a Bloch law is fitted to the low-temperature magnetization dependence.