Effect of Applied Mechanical Stressses on the Impedance Response in Amorphous Microwires with Vanishing Magnetostriction

Abstract

The effect of external (torsion and tensile) stresses on the electrical impedance of nearly-zero magnetostrictive amorphous microwires (conventional and glass covered) is reported. Glass coated Co 68.5 Mn 6.5 Si 10 B 15 microwire exhibits a maximum relative change in magnetoimpedance ratio up to around 130% at a frequency of 10 MHz, magnetic dc field of about 180 A/m and under tension of 60 MPa. This giant magnetoimpedance (GMI) effect of the microwire is affected by the magnetoelastic anisotropy induced in the sample by applying tensile stress. In addition, from the linear variations of the magnetic field H m corresponding to the maximum DZ/Z ratio, with the applied tensile stress, that is the H m (s) curve, the magnetostriction constant of this amorphous microwire (l s % --2 Â 10 --7 ) is estimated. The torsion giant impedance (TGI) ratio (DZ/Z) x has been investigated in as-cast and annealed (Co 0.94 Fe 0.06 ) 72.5 B 15 Si 12.5 conventional amorphous microwire.As-cast conventional microwire shows a slightly asymmetric Torsion Giant Impedance (TGI) and such asymmetry can be eliminated by current annealing or enhanced by current annealing under torsion. The asymmetry of (DZ/Z) x in the as-cast state and after torsion annealing could be ascribed to the spontaneous or induced helical magnetic anisotropy, which can be compensated by the application of certain torsional stress.

Improvement of giant magneto impedance of Co-rich melt extraction wires by stress-current annealing

“…As to the as-cast wires, the distribution of residual stress is inhomogeneous, which induces inhomogeneous anisotropy field. Any fluctuation in local magnetic anisotropy may change the orientation of the easy magnetization axis and substantially deteriorate the GMI magnitude [19][20]. As shown in Fig.…”

Magnetoimpedance and Field Sensitivity of CoFeSiB Amorphous Ribbons under Applied Tensile Stress

“…But the effect of tensile stress on Co-based amorphous ribbons despite of the outstanding impedance responses and the acceptable field sensitivity has been given little attentions. Gonzalez et al [13] found that the MIR in glass-covered Co-rich wires was little increased when axial tensile stress less than 100 MPa was applied, but its improvement was not significant, and a maximum value as high as 130 % at 10 MHz was observed when the tension was about 60 MPa [14]. It is known that application of an external tensile stress increases the inner core domains under stress-induced magnetoelastic field, develops an axial anisotropy, and hence reduces the MI effect [15].…”

Caracterização de materiais amorfos, através de medidas de GMI e GMI-FORC

“…Outro parâmetro que tem sido considerado para estudar a dependência da resposta GMI com o campo magnético externo é a aplicação de tensão mecânica na amostra. Por exemplo, num microfio amorfo de composição Co 68.5 Mn 6.5 Si 10 B 15 (com magnetostrição negativa e próxima a zero), com uma corrente de frequência de 10 MHz [77], aplicou-se uma tensão de 60 MPa obtendo-se um máximo de GMI de 130%, para um campo magnético de 180 A/m. Com a aplicação da tensão mecânica, foi induzida uma anisotropia transversal, que ajuda ao aumento da razão GMI.…”