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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Power-law scaling of the relaxation time associated with critical slowing down has been experimentally measured in the dynamics of the magnetization of a bilayer of iron grown on top of a W͑110͒ substrate using the complex magnetic ac susceptibility ͑T͒. The observed value of the critical exponent for the slowing down above the Curie transition of this two-dimensional Ising ferromagnetic system is z = 2.09± 0.06 ͑95% confidence͒, in agreement with most contemporary theories and simulations. Further analysis reveals that dynamical effects cause ͑T͒ to deviate from power-law scaling as the temperature is decreased towards T c , whereas the saturation of the correlation length due to finite-size effects ͑on the order of 500 lattice spaces͒ limits the divergence of .

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.

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Brillouin scattering and diffracted magneto-optical Kerr effect from arrays of dots and antidots (invited)Angular resolved Auger electron studies were carried out for Fe whisker/Cr͑001͒ interfaces which were prepared at 100, 180, 246, and 296°C. The Cr atoms penetrate progressively into the second ͑counting from the surface͒ atomic layer at 100, 180, and 246°C. At 296°C the Cr atoms enter the third atomic layer. No noticeable fraction of the Cr atoms was found in the fourth atomic layer. The exchange coupling was studied in Fe whisker/Cr/Fe͑001͒ films which were grown in a nearly perfect layer by layer mode. Magneto-optic Kerr effect and Brillouin light scattering measurements showed that the measured change in the phase of the short wavelength oscillations, the presence of a slowly varying exchange coupling bias, and the small measured values of exchange coupling are caused by the same mechanism: interface alloying. The exchange coupling in Fe whisker/Cr/nFe specimens, for nϭ10, 20, 30, and 40 ML, showed no obvious dependence on the Fe layer thickness.