Finite-Size Scaling in Thin Fe/Ir(100) Layers

The critical temperature of thin Fe layers on Ir(100) is measured through Mössbauer spectroscopy as a function of the layer thickness. From a phenomenological finite-size scaling analysis, we find an effective shift exponent $\lambda =3.15\mathrm{}\pm 0.15$, which is twice as large as the value expected from the conventional finite-size scaling prediction $\lambda =1\mathrm{}/\nu$, where $\nu$ is the correlation length critical exponent. Taking corrections to finite-size scaling into account, we derive the effective shift exponent $\lambda =(1+2{\Delta }_1)/\nu$, where ${\Delta }_1$ describes the leading corrections to scaling. For the 3D Heisenberg universality class, this leads to $\lambda =3.0\mathrm{}\pm 0.1$, in agreement with the experimental data. Earlier data by Ambrose and Chien on the effective shift exponent in CoO films are also explained.