Barkhausen jumps in a magnetic microstructure

Abstract

The magnetization process in a square dot of permalloy having a size of 20 μm and 80 nm thickness has been investigated with a focused magneto-optical 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 observation of Barkhausen jumps also in such a small magnetic sample. From a sequence of 6000 loops, systematic data on the statistical properties of these jumps have been extracted. The observed behavior shows strong deviations with respect to the available data on bulk samples and thin films.

Barkhausen noise and size effects in magnetic microstructures

“…The statistical properties of p(M i ,⌬M ) in a square dot of 20 m have been already discussed 15 for a sample having a thickness of 80 nm at variance with those discussed in the present article where the thickness is 160 nm. The most significant features for the small dot, however, are basically the same and therefore we will summarize them for the following discussion.…”

“…6,8,11,12 Recently, we proposed an experimental approach for the experimental investigation of the BN, based on a special magneto-optical ellipsometer. 13 This approach permitted us to study the BN of continuous Fe thin films 14 and to make the first measurements of the BN in a single magnetic microstructure, 15 a permalloy square dot of 20ϫ20 m. In this microstructure the statistical properties of the observed BN appear to be substantially different with respect to the usual behavior of continuous samples. In particular, the amplitude distribution of the Barkhausen jumps does not follow a power law behavior but is characterized by the presence of well defined peaks indicating that certain jumps are favored.…”

Negative Barkhausen jumps in permalloy thin-film microstructures

“…Both distributions manifest cutoff behavior associated with the sample size ͑large beam, positive jumps͒ or the beam size ͑small beam, negative jumps͒ as well as structure for large jump amplitudes attributed to the relatively small number of domain configurations that can be achieved in a microstructured thin-film sample ͑breakdown of power-law scaling resulting from finite size effects͒. 17,18 Jump-size distributions for smaller values of ⌬M x ͑for both positive and negative jumps͒ show evidence of the uniform power-law scaling observed in jump-size probability distributions in bulk 4 and larger area thin-film samples. 9 The straight lines in Fig.…”

Temperature dependent criticality of Barkhausen noise in thin Fe films

“…[3] for a complete description of the apparatus. This technique has been already used for room temperature investigations of Barkhausen noise in thin films [4] and microstructures [5].…”