Superparamagnetic field sensing devices

A ferromagnetic thin-film based magnetic field sensor, said sensor comprising:

• an electrically insulative intermediate layer, said intermediate layer having two major surfaces on opposite sides thereof;
• an initial thin-film of an anisotropic ferromagnetic material on one of said intermediate layer major surfaces;
• and
• a small hysteresis thin-film on that remaining one of said intermediate layer major surfaces of a ferromagnetic material having any retentivity measured along any lateral extent thereof parallel to said intermediate layer major surfaces being less than five percent of those values of magnitization occurring at initial magnetization saturation of said small hysteresis thin-film measured along that lateral extent for said small hysteresis thin-film also exhibiting substantially equal magnetization coercivities in either direction along that lateral extent.