Frequency selectivity of spin Hall magnetoresistance sensor and its applications in eddy current testing

Recently, we have developed a spin Hall magnetoresistance (SMR) sensor using the spin–orbit torque effective field as the built-in linearization mechanism, which allows us to achieve a linear, zero-offset, and low-noise magnetic field sensor without any dedicated magnetic bias. In this work, we examine the response of the SMR sensor to a time-varying magnetic field and demonstrate that its inherent frequency selectivity makes it uniquely suited for applications in eddy current testing. By applying a square wave current to both the coil and the sensor, and with the help of principal component analysis, we show that it is possible to detect surface cracks on an aluminum plate with dimensions down to 0.2 mm, without the need to use any sophisticated detection circuitry.