Highly Sensitive Direct Measurement of Magnetostriction and Stress Response in Near-Zero Magnetostrictive Microwires

The evaluation of magnetostriction in amorphous alloy materials, particularly in the form of microwires, has traditionally relied on indirect methods utilizing inverse magnetoelastic effects to determine the saturation magnetostriction constant, $\lambda _{\mathrm {s}}$ . In this study, we report direct magnetostriction measurements using a home-made apparatus capable of determining the engineering magnetostriction, $\lambda _{\mathrm {e}}$ , with high sensitivity down to than $\delta l/l_{o}= 10^{-9}$ as a function of the applied field, $\lambda _{\mathrm {e}}(H$ ), and its stress-dependent, $\lambda _{\mathrm {e}}(\sigma $ ), and magnetization, $\lambda _{\mathrm {e}}(M$ ), behaviors. Measurements were conducted on in-water-quenched amorphous microwires, including Co-based microwires with vanishing magnetostriction, as well as in a highly magnetostrictive microwire. In addition, the indirect method was used to calculate saturation magnetostriction constant, $\lambda _{\mathrm {s}}$ , using the complementary hysteresis loops under applied stress. For Fe-rich Fe75Si10 B15 microwires, $\lambda _{\mathrm {s}}= 31.2\times 10^{-6}$ was determined. In contrast, for Co-rich microwires, the (Co94Fe6)15Si15B10 alloy exhibited near-zero positive magnetostriction with $\lambda _{\mathrm {s}}= 9.7\times 10^{-8}$ , while (Co95Fe5)15Si15B10 displayed a slight negative magnetostriction $\lambda _{\mathrm {s}}= - 17\times 10^{-8}$ . The behavior of magnetostrictive strain under mechanical stress in near-zero magnetostrictive alloys, as observed from direct measurements, shows significant differences compared to indirect measurements found in the literature. Direct measurement of magnetostriction in amorphous microwires provides the magnetostriction value of the material according to its stress state, essential for accurately quantifying magnetostriction in sensors during operation, ensuring more precise and dependable results.