Stress-Dependent Magnetization Processes in Cobalt-Based Amorphous Microwires

Soft magnetic materials with high magnetic susceptibility in response to the influence of alternating magnetic fields, generate an inductive electric voltage in the receiving coil, the spectrum of which contains higher harmonics. This is due to the nonlinear dependence of magnetization on the magnetic field, and the amplitudes of higher harmonics make a significant contribution to the overall signal if an external field leads to magnetic saturation. Magnetic susceptibility and saturation field are largely determined by magnetoelastic interactions in amorphous ferromagnets, respectively, the amplitudes of higher harmonics should depend on external mechanical stresses. In this work, we study the processes of magnetization reversal in amorphous microwires of two compositions: Co₇₁Fe₅B₁₁Si₁₀Cr₃ and Co_66.6Fe_4.28B_11.51Si_14.48Ni_1.44Mo_1.69 under the action of external tensile stresses. For the first composition, mechanical stresses exceeding a certain limit (higher than 350 MPa) lead to the transformation of the magnetic hysteresis from a bistable type to an inclined one. In this case, a sharp change of the harmonic spectrum is observed. In microwires of the second composition with an initially inclined loop, external stresses cause a monotonous increase in the slope of the hysteresis loop (a decrease in susceptibility). In this case, the amplitudes of higher harmonics change significantly at low stresses, lower than 100 MPa. The results were obtained by magnetization reversal of microwire samples using a system of flat coils, which demonstrates the potential of using these materials as wireless sensors of mechanical stresses with remote reading.