Critical behavior of the uniaxial ferromagnetic monolayer Fe(110) on W(110)

The critical behavior of a ferromagnetic monolayer has been investigated experimentally for the case of the thermodynamically stable pseudomorphic monolayer Fe(110) on W(110). The nearly ideal monolayer samples were composed of monolayer Fe(110) stripes, grown by step flow from the atomic steps of the W(110) substrate, with a distribution of stripe widths around a mean value of 40 nm, and virtually infinite length. The magnetic properties were measured by spin-polarized low-energy electron diffraction, which could be done in weak magnetic fields up to 2 Oe. The monolayer samples show uniaxial magnetic anisotropy with the easy axis [$1\overline{1}0$] in the film plane. Magnetization tails above $T_c$ were shown to be a result of convolution of the critical power law with the monolayer stripe width distribution. Using an appropriate deconvolution, critical power laws could be established for both magnetization $M$ and susceptibility $\chi$, with critical exponents $\beta =(0.134\mathrm{}\pm 0.003)$ and $\gamma =(2.8\mathrm{}\pm 0.2)$, corresponding to predictions of a two-dimensional anisotropic Heisenberg model.