Magnetic field cameras exist:
https://matesy.de/en/products/cmos-magview
https://en.wikipedia.org/wiki/File:Visualization_of_magnetic...
Magnetic field cameras exist:
https://matesy.de/en/products/cmos-magview
https://en.wikipedia.org/wiki/File:Visualization_of_magnetic...
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Could you use them on a hard disk platter? Is there software out there for recovery of data from a set of platters taken from a bad HDD for which replacement heads / doner drives are not longer available?