CRITICAL SPIN FLUCTUATIONS AND CURIE TEMPERATURES OF ULTRATHIN NI(111)/W(110) - A MAGNETIC-RESONANCE STUDY IN ULTRAHIGH-VACUUM

Ferro- and paramagnetic resonance is performed in situ in ultrahigh vacuum on 15- to 40- thin Ni(111) films from 300 to 630 K. As a function of temperature a huge peaklike broadening of the linewidth Hpp is observed. From the thickness dependence of this peak we deduce the Curie temperatures Tc(d) of the respective films with thickness d, e.g., Tc(15) =512 K=0.81Tc(bulk). The shift exponent of the thickness dependence of Tc is determined to be 1.42±0.3. The temperature dependence of Hpp below Tc is analyzed in terms of Hpp(1-T/Tc)-, with the critical exponent of the spontaneous magnetization. ranges from 0.38 for bulk Ni to 0.29 for 15- film. © 1990 The American Physical Society.