Scanning Hall probe microscopy of residual magnetic fields around plastic deformation of Vickers indentations in carbon tool steel (JIS, SKS93)

• We developed a scanning Hall probe microscope equipped with a GaAs film sensor.
• We observe the magnetic flux density at the steel from several lift-off distance.
• The reduction of lift-off distance is effective to observe the magnetic fields.
• It is possible to observe the magnetization caused by plastic deformation.

In this paper, improvement of the magnetic field detection accuracy of Scanning Hall probe microscopy (SHPM) by reducing the lift-off distance was studied. The distribution of the three dimensional residual magnetic flux density components was observed around the magnetization point on the surface of carbon tool steel at several lift-off distances ranging from 350 μm to 1500 μm. The observation at 350 μm lift-off distance achieved more 2.7 times intensity than at 1500 μm lift-off distance and a correlation between the magnetic flux density and the lift-off distance was found. Based on the 350 μm lift-off observation, a successful observation of magnetization caused by plastic deformation around the Vickers indentation was succeeded to be performed.