70 faranheit= 21celcius.gadi's transition is 16 celcius.maybe you've got the para-magnetic properties going there.put in some warm water to warmup and chek if it still does this

Or bring the whole setup near the kitchen toaster,oven or lounge heater and chek if it still does this..

So measure ohms across the face of the coin?

Hold on.did you check if the magnets still hold near the oven

This may be important