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We measured the statistical properties of Barkhausen noise in finemet films with nominal composition Fe73.5Cu1Nb3Si22.5B4 and variable thickness between 25 and 1000nm. Films have been sputtered on glass substrates and their structure is amorphous. The critical exponents of the power-law distributions for the jumps amplitude show a remarkable stability over the whole thickness range, whereas the other macroscopic magnetic properties undergo strong variations. The value of the critical exponent is about 0.8 between 50 and 500nm with a small increase up to 1.0 at 1000nm. These values are similar to those observed with the same experimental technique in other two-dimensional (2D) systems, but definitely smaller with respect to the values observed in truly three-dimensional (3D) systems. Our data therefore indicate that, in the investigated thickness range, the behavior remains typical of 2D systems. The small increase of the critical exponent at 1000nm might be an indication of a starting transition toward a 3D behavior.

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The probability distribution of the amplitude (ΔM) of Barkhausen jumps during magnetization reversal in thin films can be measured with optical techniques since each jump produces a variation (ΔI) of the laser beam intensity used to probe magnetization. Here we present a theoretical model which demonstrates that no distortion takes place if P(ΔM) is a power law [P(ΔM)=ΔM−α] with (α>=1.0). This prediction has been experimentally confirmed by measuring P(ΔI) in the same experimental conditions but in two different ways: first with a Gaussian and then with a constant intensity laser profile. In both cases the same power-law distribution has been observed with α=1.0.