Temperature Dependence of Giant Magnetoimpedance in Amorphous Microwires for Sensor Application

Temperature dependence of giant magnetoimpedance (GMI) amorphous wires has been investigated in a quasi-industrial temperature range of [-20 degrees C; 120 degrees C]. Co-rich amorphous microwires, from Unitika Ltd, of 100 mu m diameter and about 50 mm length were placed inside a regulated temperature chamber. The impedance modulus, as a function of the magnetic field, was measured using an impedance analyzer. The excitation current of the GMI wire was about 3 mA of amplitude and 1 MHz of frequency. In addition to the GMI ratio, particular attention was paid to the behavior of the intrinsic sensitivity and the offset, which are the most relevant quantities in a real GMI sensor implementation. The experimental results have showed that the impedance curve was changed with the temperature. The maximum sensitivity and the GMI ratio increased with temperatures ranging from -20 to 80 degrees C. Then, beyond 80 degrees C, the trend seemed to be reversed. Over the considered temperature range, and at typical bias field of H = 35 A/m, the intrinsic sensitivity varied with a temperature coefficient of 0.4%/degrees C, while the temperature coefficient of the offset was about 200 nT/K.