CONICET | Buscador de Institutos y Recursos Humanos

The evaluation of the magnetostriction in amorphous alloy materials, particularly in the shape of microwires, has been performed typically making use of indirect methods through the inverse magnetoelastic effects (e.g., the Small Angle Magnetization Reversal, SAMR) that in some cases is not fully reliable (e.g., samples with positive magnetostriction) [1]. Here, we report first direct magnetostriction measurement by direct detection of the magnetostrictive elongation produced by the magnetization rotation under applied axial magnetic field, H. For that, we use a home-made equipment with suitable induction and pickup coils, mechanical system to apply tensile stress and a high-accuracy Linear Variable Differential Transformer, LVDT, to evaluate the microwire elongation, l/l [2]. Measurements were performed on three different types of amorphous microwires: a) Highly magnetostrictive: i) Two in-water-quenched Fe75Si10B15 microwire (diameters, D= 145 μm and 85 μm, respectively), and ii) Pyrex-coated Fe79Si8B9C4 microwire (D= 16 m), and b) Vanishing magnetostriction: iii) Co-based microwires, (Co94Fe6)15Si15B10, and (Co95Fe5)15Si15B10, with D= 155 m. The results are studied together with magnetization, M, measurements under the same mechanical stress, . The figures show representative data where the high-sensitivity of the equipment to quantify direct magnetostrictive elongation is observed (down to l/l=10-8). Data are analysed considering the stress dependence of the fractional volume of transversely magnetized domains, the only truly involved in the magnetostrictive elongation which is particularly relevant in the case of highly-magnetostrictive bistable microwires. This method to properly quantify the magnetostriction of amorphous microwires is of particular relevance as required in sensing elements of various mechanical sensor devices.

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