An ${\mathrm{FeBO}}_3$ single crystal was studied from 291 K up to the Néel temperature $T_N=348.35\mathrm{}\mathrm{K}$ by depth selective conversion electron Mössbauer spectroscopy in ultrahigh vacuum $\left({10}^{-9\mathrm{}}\mathrm{mbar}\right)$. A new magnetic near-surface phase was found. Its thickness $D$ diverges on approaching $T_N$ and gives a critical exponent for the correlation length of $\nu =0.59\mathrm{}\left(4\right)$. The phase boundary between the bulk and near-surface phase could be identified.

• Received 22 October 1999

DOI:https://doi.org/10.1103/PhysRevLett.84.5632