I remember the first time that I heard of a micro (or quantum) black hole. It was in the short story "The Hole Man" written by Larry Niven in the early seventies. I think I read it in the late seventies. A quantum black hole is held in a containment field found in an abandoned alien artifact on Mars. The protagonist shuts off the containment field as the antagonist is passing under it, the black hole dropping through him, killing him and ultimately dooming the planet to eventual destruction as the hole now continuously orbits Mars' interior destroying everything in its path one molecule at a time.
The artifact was (if I remember correctly) thought to be some kind of alien communication device, one that transmitted gravity waves.
Anyway, you could make a tractor beam with magnetism but anything sufficiently strong enough to exert the required pull on a craft would almost certainly mess up the biologicals on board. That's why I thought that gravity would be better. The containment and focusing would be the trick. Too much gravity would be as bad as too great a magnetic field, killing the occupants with tidal forces.
Anyway, Niven had lots of great concepts like that when he was in his prime. If you are at all inclined toward scifi you could do a lot worse than to start out with Niven's Known Space series of short stories and novels which culminates with the multi-award winning Ringworld.