A new frequency-modulation-type MI sensor

A new frequency modulation-type magneto-impedance (MI) sensor was developed, in which the Fe-based nanocrystalline MI element works as an inductive element. The amorphous Fe/sub 73/Cu/sub 1/Nb/sub 1.5/V/sub 1/Si/sub 13.5/B/sub 9/ ribbons were fabricated by single-roller quenching technique. Samples were annealed under different tensile stress from 0 and 245 MPa at 540/spl deg/C for 30 minutes and were cooled down to room temperature in the nitrogen atmosphere. The sample with the length of 4 cm was placed in a small solenoid, forming a MI element. The magnetic property was characterized by the dynamic hysteresis and the corresponding Ml curves were measured. A maximal sensitivity of 42%/Oe has been achieved using the ribbon sample annealed under 16.7 MPa. The oscillation frequency can be linear with dc external magnetic field in larger range by changing the transverse magnetic anisotropy. A 4 Oe linear region of dc magnetic field was obtained for the sample annealed under 59.8 MPa.