Volumetrically scanning the structure of stray-fields above grain-oriented electrical-steel using a variably angled TMR sensor

A new versatile scanning hardware based on a Micromagnetics
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STJ-020 MgO-based tunnelling magnetoresistance (TMR) sensor has been developed to volumetrically scan the thin boundary layer above a given sample. An (x, y) planar scan of the surface of a 7.5 mm × 7.5 mm sample of grain-oriented (3% Si) electrical steel is presented. Stray fields normal to the surface between -116 and 272 A/m are measured. At 10 q, m/pixel domain and micro-domain structures are seen. At 5 q, m/pixel the micro-domain structures resolve into clear Lancet domains. The domain images presented have greater qualitative similarity with Kerr effect observations than with Bitter technique results. An (x, z) vertical scan along a 2.35 mm transect reveals the perpendicular extent of the stray fields, with the normal components shown to emanate from the domain bodies and extend approximately 40-100 q, m from the sample surface. With the aim of investigating how the stray fields close back onto the surface, the (x, z) transect is repeated with the sensor at 5, 10, 15 and 20 degrees from the vertical. For the first time, the stray fields from surface domains viewed by other techniques in only a planar (x, y) projection have been studied in the (x, z) plane perpendicular to the surface.