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

Abstract

The critical temperature of thin Fe layers on Ir(100) is measured through M\"ossbauer spectroscopy as a function of the layer thickness. From a phenomenological finite-size scaling analysis, we find an effective shift exponent $\ensuremath{\lambda}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}3.15\ifmmode\pm\else\textpm\fi{}0.15$, which is twice as large as the value expected from the conventional finite-size scaling prediction $\ensuremath{\lambda}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}1/\ensuremath{\nu}$, where $\ensuremath{\nu}$ is the correlation length critical exponent. Taking corrections to finite-size scaling into account, we derive the effective shift exponent $\ensuremath{\lambda}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}(1+2{\ensuremath{\Delta}}_{1})/\ensuremath{\nu}$, where ${\ensuremath{\Delta}}_{1}$ describes the leading corrections to scaling. For the 3D Heisenberg universality class, this leads to $\ensuremath{\lambda}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}3.0\ifmmode\pm\else\textpm\fi{}0.1$, in agreement with the experimental data. Earlier data by Ambrose and Chien on the effective shift exponent in CoO films are also explained.