I would like to know who was the first using a magnet with this effect, and in what year that method was first used.

I just found out that the German magician Chess Litten described her method in using a magnet and a metal plate in the German MAGIE magazine in February 1991.

This doesn't surprise me. There are a number of pieces of magic that have been spotted overseas and then duplicated here. It actually goes both ways.

I've seen some German magic magazines, mainly local club newsletters, in which almost all the material was translated from books from other countries. Sometimes this was with credit, sometimes not.

Back when there were two Germanies, Punx was shocked to find his entire patter for "Kismet" in Setzt Euch zu meinen Füßen knocked off by Herbert M. Paufler (who made the original props for Punx) and published in an East German magic magazine under the name "Guru." The original Guru prop is in the possession of Alex Roemer.

So, we see that the American "originators" of the magnet and plate "originated" it much later than the Germans did.