Dimensional Cross-Over in Thin Film Spin-Glasses

Measurements of the electrical transport in the presence of a magnetic field for very thin spin-glass films of AuMn, AgMn and AuFe alloys, are reported. The influence of the effective dimensionality on the spin-glass order is studied by varying the film thickness between 4nm and 40nm. Weak electron localization and spin-glass resistivity measurements only provide a qualitative picture of the transition from spin-glass to Kondo behaviour in the thinnest films. Measuring the temperature dependence of the Hall resistivity on the other hand directly reflects the thickness dependence of the freezing temperature T f . Our results clearly indicate that dimensionality effects as well as the reduced elastic mean free path influence the spin-glass transition. The experimental correlation length exponent v = 0.8 is smaller than the theoretically predicted value.