Spin-valve film for sensitive giant magnetoresistive sensor using AC bias magnetic field

A giant magnetoresistive material for a new sensitive magnetic sensor eleme nt was developed by a NiO spin-valve film. The magnetic sensor is composed of a multilayered structure that includes the spin-valve element and a bias current line. High sensitivity is obtained by using only the (rising or fa lling) edge of the magnetoresistive (MR) loop. hn AC bias magnetic field in duced by a square-wave bias current (plus or minus) is applied to the spin- valve element. The bias magnetic field is set to be slightly smaller than t he rising field. The resistance of the spin-valve element is constant, if a n external magnetic field is not applied. The output signal synchronizes wi th the input bias current, if the bias field is made to cross the rising ed ge of the MR loop by applying an external magnetic field. The spin-valve fi lm: [NiO/NiFeCo/Cu/NiFeCo] exhibits the appropriate properties for the sens or element, such as an MR ratio of 5.1%, a sensing field of 0.2 kA/m, a dri ving field of 1.4 kA/m, an element destroying field of 32 kA/m and a high c orrosion resistance. Moreover, the spin-valve element, patterned to a micro scopic size, exhibits a step-shaped MR loop in which a free-layer magnetiza tion switches like a single domain. The magnetic sensor using this spin-val ve film detects an external field change of 0.04 kA/m, and operates at 30 n s.