Papers by Keyword: Magnetic Bistability

Abstract: We have studied the influence of the thermal treatment on the stress dependence of the switching field during the devitrification of amorphous Fe_73.5Cu₁Nb₃Si_11.5B₁₁ microwires. The non-destructive test (NDT) method based on the magnetization reversal of ferromagnetic materials is sensible to changes in microstructural characteristics and the stress state of the material. The stress dependence has been explained considering the magnetoelastic contribution to the switching mechanism which is modified applying the tensile stresses and changing the magnetostriction constant and strength of the internal stresses distribution through thermal treatments. We show that by properly setting a frequency during the measurement and adequate treatment of the sample, it is possible to vary the sensitivity, magnitude and stress dependence of the sample. Keywords: Magnetic bistability, glass-coated microwires, switching field, stress sensor

Abstract: Glass coated microwires with two metallic nucleus compositions Co57Fe 6.1Ni10B15.9Si11 and Fe36,4Co41,7B11,8Si10,1 with 3 different glass coating compositions (Pyrex – 74.5% SiO2, 15% - B2O3, 3%- Na2O, 2%- Al2O3 1.5% -K2O; Nonex – 73% SiO2, 16.5% - B2O3, 6% - PbO 3 %-Na2O, 1.5% -K2O; and F1 – 70.2% SiO2, 27% - B2O3, 0.8 %-Na2O, 2%- LiO2 1% -K2O;) with very similar geometry (metallic nucleus diameter 7 µm, total diameter 19 µm) have been successfully fabricated and studied. Ferich microwires in as-prepared state show rectangular hysteresis loops, which is connected with the strong internal stresses induced by the fabrication process. Co-rich compositions show inclined hysteresis loop with smaller value of coercive field. The coercivity, Hc, of Co-rich microwires is the highest and of Ferich samples is the lowest in the case of Pyrex coated microwires. The Nonex coated microwires are in the intermediate position while the F1 coated Co-rich microwires have the lowest Hc while the Fe-rich samples have the highest Hc. The mechanical tests show that the best tensile strain yield is observed in samples coated by Nonex glass followed by Pyrex and F1. In this way the variation of the glass coating material allows to tailor both magnetic and mechanical properties of glass coated tiny microwires.