Sulla relazione tra effetto Barkhausen e legge di Rayleigh

Riassunto

L'A verifica sperimentalmente, sui vari tipi di materiali magnetici, che la legge diRayleigh, relativa al comportamento dei materiali magnetici sottoposti a valori di campo bassi rispetto al valore del campo coercitivo massimo, cessa di avere validità a quel valore di campo per il quale compare l'effettoBarkhausen. Si verifica così che l'ipotesi fondamentale, sullá quale si basa l'interpretazione data daNéel alla legge diRayleigh, è esatta.

Summary

The author experimentally prooves that theRayleigh law, referring to the behaviour of magnetic materials subjected to magnetic force values low in comparison of the values of the maximum coercive force, ceases being valid at that force value by which theBarkhausen effect takes place. Such test have been performed on ordinary soft iron, commercial pure iron, carbon steel, hard and annealed nickel, Hipernik (50 Ni, 50 Fe). For silicon steel too, whose anomalous behaviour as to theRayleigh law is well known it is possible to find, on the plot of the permeability against the magnetic force, a characteristic point which identifies itself with the force value by which the threshold of theBarkhausen effect is got: the point at which the concavity towards the abscissa's axis ends.

The number of the examined materials is slight if compared with the total number of magnetic materials, but, since they belong to substantially different types, the following conclusion does not seem arbitrary: the validity of the law up to that force value by which theBarkhausen effect begins to take place is a general property of magnetic materials.

Néel has lately given a theoretic interpretation of theRayleigh law. The fundamental hypothesis on which such theory relies is that the magnetic force value, to which the fragment of material is subjected, must be little enough not to cause reversals or changes of directions of magnetization inWeiss domains. The referred tests confirm the validity ofNéel's hypothesis.