Engineering of Magnetic Softness and Domain Wall Dynamics of Fe-rich Amorphous Microwires by Stress- induced Magnetic Anisotropy

Abstract

We observed a remarkable improvement of domain wall (DW) mobility, DW velocity, giant magnetoimpedance (GMI) effect and magnetic softening at appropriate stress-annealing conditions. Beneficial effect of stress-annealing on GMI effect and DW dynamics is associated with the induced transverse magnetic anisotropy. An improvement of the circumferential permeability in the nearly surface area of metallic nucleus is evidenced from observed magnetic softening and remarkable GMI effect rising. We assumed that the outer domain shell with transverse magnetic anisotropy associated to stress-annealing induced transverse magnetic anisotropy affects the travelling DW in a similar way as application of transversal bias magnetic field allowing enhancement the DW velocity. Observed decreasing of the half-width of the EMF peak in stress-annealed microwires can be associated to the decreasing of the characteristic DW width. Consequently, stress annealing enabled us to design the magnetic anisotropy distribution beneficial for optimization of either GMI effect or DW dynamics.

Optimization of magnetic properties and GMI effect of Thin Co-rich Microwires for GMI Microsensors

“…However, as mentioned above, in the case of studied microwires, higher T ann and σ (as compared to Fe-rich microwires) are requested to observe considerable transverse magnetic anisotropy [41][42][43][44][45][46][47][48][49]. Therefore, observed stress-annealing-induced anisotropy can present similar origins for the case of Fe-rich microwires, i.e., either back stresses or topological short-range ordering [41][42][43][44][45][46][47][48][49]. The particularity of glass-coated microwires is that they are essentially composites consisting of metallic alloy nucleus and glass-coating that induces strong internal stresses [35][36][37][38][39].…”

“…For intermediate Tann and σ values, stress-annealed microwires present lower coercivity (20 ≤Hc ≤ 25 A/m for 200 °C≤Tann≤ 350 °C and σ ≤ 354 MPa) and higher squareness ratio (Mr/Mo≈0.97 for 200 °C≤Tann≤ 350 °C and σ ≤ 354 MPa). For comparison, remarkable transversestress-annealing-induced magnetic anisotropy has been reported for Fe75B9Si12C4 microwire annealed at Tann =300 °C (σ =380 MPa) or Tann =325 °C (σ =190 MPa) [49].…”

“…The origin of stress-induced anisotropy in amorphous materials is still not clear, although it is discussed in numerous publications [60][61][62]. The most common origin of stress-annealing-induced anisotropy is either "back stresses" or directional pair (chemical or topological) ordering [41][42][43][44][45][46][47][48][49][60][61][62]. Annealing:…”

“…The schematic picture of the experimental setup is provided in Figure 1. The electromotive force, , in the pick-up coil with N turns produced by the change of magnetic flux, φ, is given by the following equation [29,49]: The microwire occupies a small part of the coil cross-section. Therefore, the magnetic flux produced by the external field can be essentially relevant, and hence it is necessary to consider both parts of magnetic flux, originating from the sample magnetization, M, and from the magnetic field, H: The microwire occupies a small part of the coil cross-section.…”

“…Hysteresis loops can be represented as the normalized magnetization, M/M o , versus the applied magnetic field, H, where M o is the magnetic moment of the sample at the maximum magnetic field amplitude, H o [49].…”