Abstract
Magnetoimpedance (MI) effect in amorphous ferromagnetic microwires represents is the ideal base for sensing technology and is currently used to develop high sensitive sensors of weak magnetic fields with a resolution up to few micro−Oersteds. The effect of heat treatment on off−diagonal MI in glass coated ferromagnetic amorphous microwires has been studied in order to improve MI sensitivity and temperature stability. We have shown the dependence of sensor signal on temperature. The wires had Co−based composition and internal stress induced helical or circumferential anisotropy. We have demonstrated that annealing of the entire sensing element including the electric contacts and the detection coil may improve the sensitivity of the output signal to an external magnetic field by about 25% and decrease its temperature sensitivity almost twofold in the −30…+80 °C range. These improvements require strict control of the annealing parameters. The best results are obtained for annealing at 160 °C for 2−3 minutes. The experimentally observed changes are related with stress relaxation during annealing; in particular; relaxation of the stresses occurring during solidification due to the difference in the thermal expansion coefficients of the metal core and the glass sheet.
Highlights
Magnetoimpedance (MI) effect in amorphous ferromagnetic microwires represents is the ideal base for sensing technology and is currently used to develop high sensitive sensors of weak magnetic fields with a resolution up to few micro−Oersteds
The effect of heat treatment on off−diagonal MI in glass coated ferromagnetic amorphous microwires has been studied in order to improve MI sensitivity and temperature stability
We have demonstrated that annealing of the entire sensing element including the electric contacts and the detection coil may improve the sensitivity of the output signal to an external magnetic field by about 25% and decrease its temperature sensitivity almost twofold in the −30...+80 °C range
Summary
Магнитоимпедансный эффект в ферромагнитных аморфных микропроводах является идеальной основой для разработки высокочувствительных сенсоров слабых магнитных полей с разрешением до нескольких микроэрстед. В процессе изучения данного явления была разработана методика термической обработки датчиков на основе аморфных микропроводов и проведено исследование влияния режимов отжига на чувствительность и температурную стабильность недиагонального магнитоимпеданса в микропроводах. Магнитная структура аморфных микропроводов может быть модифицирована за счет изменения внутренних механических напряжений в результате различных тепловых обработок [8, 9]. Отжиг микропроводов состава Co66,94Fe3,83Ni1,44B11,57Si14,59Mo1,96 с общим диаметром 45 мкм и диаметром металлической жилы 42 мкм при температуре 200—300 °С в течение 5 мин приводит к изменению анизотропии с циркулярной на осевую, что подтверждается как поведением петли гистерезиса намагничивания провода, так и его МИ−характеристиками [9].
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