Internal Friction of Ferromagnetic Materials

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Abstract
It is common knowledge that in cyclically stressed ferromagnetic materials an energy loss due to internal friction is observed; this part of loss disappears when the material is brought to saturation or above the Curie temperature. It is also known that a stress, applied to a ferromagnetic material, produces a motion of Weiss domains from their rest position. The scope of this paper is to verify experimentally the following hypothesis: in cyclically stressed ferromagnetic materials, energy loss because of magneto‐elastic internal friction is induced by a domain motion due to the applied stress itself. The ratio Ir/Is (where Ir=residual induction, and Is=saturation intrinsic induction) has been chosen as an index of the domain position; its measure has been carried out by normal ballistic method on a permeameter rigged with a torsion applying device. Energy loss was measured by means of a torsion pendulum; a coil allowed the saturation of specimen in order to separate magneto‐elastic from purely mechanical losses. Plotting curves of Ir/Is and of magneto‐elastic losses as a function of applied stress and comparing them for each tested material, it has been found that they, besides having the same shape, show abrupt slope variations at practically the identical value of stress. It has further been observed that a specimen presenting only a low percent variation of Ir/Is ratio (i.e., in which domains had slightly moved from their rest position) showed also moderate magneto‐elastic losses. These results appear to confirm assumptions made about the magneto‐elastic internal friction in ferromagnetic materials. The reason why motion of domains takes place in an essentially irreversible way still remains unknown.

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