Static and Dynamic Critical Phenomena in Ultrathin Films of Iron on W(110)

Abstract

<p>The critical properties of Fe/W(110) ultrathin films with thickness between 1.5 and 2.0ML have been studied using magnetic ac-susceptibility Xm. Using a careful statistical fitting routine that allows simultaneous extraction of the critical exponent Υ and the transition temperature Tc , the Fe/W(110) films were found to belong to the 2d Ising universality class. Measuring the 2d Ising Υ value of 7/4 from the data appears to be dependent on how close to Tc the data allows fitting. This in turn is dependent upon film thickness, likely through changes in film uniformity. For measurements of the susceptibility that show power-law scaling below a reduced temperature value of 4.75x10⁻³, the average value of Υ= 1.75±.02. Further analysis of the complex susceptibility allows the extraction of the critical slowing down exponent z. It has been found that bilayer films that exhibit a static critical exponent Υ near 1. 75 show a value of z = 2.09±.06 (95% confidence). This finding represents the first experimental measurement of the critical slowing down exponent which supports the current theoretically predicted value for a 2d Ising system. Further analysis also allows insight into various saturation processes that affect the magnetic ac-susceptibility near Tc and the effect that oxygen doping of the surface has on the saturation.</p>