AC-susceptibility of Ni/W(110) ultrathin magnetic films: determination of the Curie temperature and critical behavior

The temperature dependence of the magnetic susceptibility of 6-8 ML Ni/W(1 1 0) is measured in situ in UHV by means of an AC-susceptibility mutual ind uctance bridge. At sufficient small driving magnetic fields less than or eq ual to 11A/m a susceptibility maximum and an interval of constant susceptib ility on the high temperature side of the peak are observed. The Curie temp erature is identified as the low temperature limit of this region of consta nt susceptibility. The appearance of the maximum at lower temperatures is i nterpreted as a ferro-magnetic response at T < T-C. The critical exponent g amma is extracted from a power law fit at T > Tc. For the smallest field of 3 A/m, the determined gamma of 1.26 (7) is consistent with gamma of the th ree-dimensional Ising model. For larger fields, the exponent depends on the field and presents an effective value. (C) 2001 Elsevier Science B.V. All rights reserved.