Sensitive Giant Magnetoresistive Sensor Using AC Bias Magnetic Field

Abstract

In this paper, we propose a new sensitive magnetic sensor consisting of a multilayered structure that includes a NiO spin-valve element and an AC bias current line. The spin-valve element, patterned to a microscopic size, exhibits a step-shaped magnetoresistive (MR) loop in which a free-layer magnetization switches like a single domain. High sensitivity is obtained by using only the (rising or falling) edge of the MR loop. An AC bias magnetic field induced by a square-wave bias current (plus or minus) was applied to the spin-valve element The bias magnetic field was set to be slightly smaller than the rising field. The resistance of the spin-valve element is constant, if an external magnetic field is not applied. The output signal synchronizes with the input bias current, if the bias field is made to cross the rising edge of the MR loop by applying an external magnetic field. Our magnetic sensor detects an external field change of 0.5 Oe. A high-performance magnetic sensor can be obtained by monitoring the switching value change in a ramp-shaped bias current in which the strength continuously changes. The direction and value of the slight change in the external magnetic field were measured with high resolution.