Magnetic stray field mapping of stainless steel sheets using spin Hall magnetoresistance sensor

Recently, we have developed a spin Hall magnetoresistance (SMR) sensor featuring high-sensitivity, low-noise, zero-offset, and negligible hysteresis. Here, we demonstrate that the SMR sensor can be used to map the self-magnetic leakage field (SMLF) of stainless steel sheets. The SMLF serves as an effective knob for probing magnetism in steel sheets induced by either stress or composition inhomogeneity, which, in turn, affects its mechanical properties and corrosion resistance. However, the SMLF is typically quite weak, and thus the high-sensitivity and low-noise SMR sensor is uniquely suited for this application. The self-magnetic flux leakage mapping experiments have been conducted on SUS304 steel sheets with emphasis on the lift-off effect. Both analytical model and finite element modeling have been used to account for the experimental results. Although the SMLF mapping alone is unable to pinpoint the root cause of magnetism, i.e., whether it is due to stress or composition inhomogeneity, it does provide an efficient way for pre-screening of steel sheets to prevent defect formation at early stages.