Magnetoimpedance of magnetic amorphous alloys, measured by a contactless technique

The strong magnetoelastic (ME) coupling in magnetic amorphous alloys (MAA) have been exploited for measuring a variety of physical parameters, such as mass, density, viscosity, humidity, or temperature. When a longitudinal magnetic field is applied, a ribbon of MAA also changes its length. If the magnetic field is then oscillated with variable frequency, a strong induced electromagnetic response (emf) can be detected in a pick-up coil when the oscillating frequency matches the mechanical resonance of the ribbon. The implications on the magnetoimpedance of MAA ribbons have not been explored much, possibly due to the challenge associated with losses through the contacts. Here, we first show that, using a radiofrequency (rf) resonator technique, the rf-impedance can be measured without the need for contacts. Then, we show that magnetoimpedance shows strong and unusual field dependence, both at room and cryogenic temperatures. We will discuss possible origins of our findings and propose new sensing applications of MAA materials.