Technics apparently made a couple of cassette decks with hall effect playback heads. A brief search turned up this thread from a couple of years back from another forum:
http://www.tapeheads.net/showthread.php?t=28418
I remember reading about it in one of those 'which tape recorder to buy' type magazines at the start of the 1980s. One advantage was that the low end frequency response extended very far down; in essence the head by virtue of its design could read pure DC from the tape.
... except that reading more, it seams the head was based on MR ('magnet resistive' according to the owner's manual), which is not the same thing as the hall effect. Ah well, at any rate it was not a run-of-the-mill coil, laminations and gap type head.
Yet more detail on this type of head and the connection with Philips and DCC here:
https://www.tapeheads.net/showthread.php?t=8817