Thor vs Magneto
This is from JOURNEY INTO MYSTERY# 109, back in October 1964. Script by Stan Lee, art by Jack Kirby (with Chic Stone inking). I want to put up the whole story with annotations because it has some interesting aspects.
One aspect of Kirby that I don't really like is that he gave his heroes new abilities left and right as needed. Here Thor draws out Magneto's force field with his hammer. In one story (with the Tomorrow Man) Thor used his hammer to channel "the magnetic forces off the galaxy" to bring down a robot, focus the "alpha rays in the atmosphere" to break up some guns, and put people in a hypnotic trance by catching sunlight on the polished faceof Mjolnir. He never used the abilities before or since. I love Kirby's art and storytelling, but as a rule it's not a good idea to give your hero unexplained powers for a one-time use.
Magneto in some stories could affect people by using magnetism on the iron content of their blood. I don't think so. We do have iron in our blood but it's not in a state where magnetism affects it. Otherwise, when you go into an MRI, you'd be ripped apart. But comics do regard the laws of physics as mere suggestions.