The critical phase transition in ferromagnetic ultrathin Fe/W(110) films has been studied using the magnetic ac susceptibility. A statistically objective, unconstrained fitting of the susceptibility is used to extract values for the critical exponent γ, the critical temperature Tc, the critical amplitude χo and the range of temperature that exhibits power-law behaviour. A fitting algorithm was used to simultaneously minimize the statistical variance of a power law fit to individual experimental measurements of χ(T). This avoids systematic errors and generates objective fitting results. An ensemble of 25 measurements on many different films are analyzed. Those which permit an extended fitting range in reduced temperature lower than approximately 4.75 × 10 −3 give an average value γ=1.76 ±0.01. Bilayer films give a weighted average value of γ = 1.75 ± 0.02. These results are in agreement with the 2-dimensional Ising exponent γ= 7 4 . Measurements that do not exhibit powerlaw scaling as close to Tc (especially films of thickness 1.75ML) show a value of γ higher than the Ising value. Several possibilities are considered to account for this behaviour.

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The electron-hole excitations with different spin con6gurations have been separated and studied experimentally in iron, with use of spin-resolved electron-energy-loss spectroscopy with both a source and detector of spin-polarized electrons. The data are interpreted using a two-particle, exchange scattering model, and analyzed in the 4&(4 product spin space of the incident and target electrons. Stoner excitations in the form of majority-hole-minority-electron pairs are found to comprise up to one-third of the total electron-hole excitations in off-specular scattering, and exhibit a clear, broad peak due to excitations within the exchange-spht d bands of iron. The width and energy loss at which this peak occurs increase with increasing wave vector of the Stoner excitation. These trends are also observed in the calculated Stoner density of states for iron.