magnet and mircrowaves

No.

As experiment you can place your big wooden speakers from the living room near the microwave oven in the kitchen, and you see that still can heat up your pizza.
:D

But the microwave oven is in an shield enclosure for the example you quote.

Electromagnetic waves don't interact with static electric or magnetic fields in regular dielectric media. Also with special media, you can't direct waves but some interaction exists:http://en.wikipedia.org/wiki/Faraday_rotation

Can you refrase your question?
you want to know a way to find the polarization of a microwave signal?