The magnetization process in a square dot of permalloy having a size of 20
mu m and 80 nm thickness has been investigated with a focused magneto-optic
al hysteresigraph. With this apparatus, it is possible to measure in a few
seconds the hysteresis loop with a signal-to-noise ratio adequate for the o
bservation of Barkhausen jumps also in such a small magnetic sample. From a
sequence of 6000 loops, systematic data on the statistical properties of t
hese jumps have been extracted. The observed behavior shows strong deviatio
ns with respect to the available data on bulk samples and thin films. (C) 2
000 American Institute of Physics. [S0003-6951(00)03017-5].