Not exactly. The material used is still up for debate. It could be metal, it could be a rock, it could be a crystal or it could be a mix. Even if it was pure metal, the shields would prevent Mags from taking it off. Furthermore, if he did manage to get it off, the GL can just will it right back to him/herself.
lol. what IS that,
anyway, magneto can control all matter with his magnetism, anythin, even a green lantern ring, its made of matter right, its only the power thas infused INTO the ring that makes it strong, ofcourse gl could try n use his own mental power to counter any type of physical force prodused by mags, but i doubt any green lantern can produce enough power to actually resist the level that magneto produces.