Dimensional Cross-Over in Thin Film Spin-Glasses

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Abstract
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 Tf. 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.