As Magneto has control of magnetism, can he create darkness? Light itself is an electromagnetic wave, and eliminating the magnetic part of light might cause it to be “invisible” to the human eye.
First of all, you can't "eliminate the 'magenetic' part of light". That's not how physics works. You can ask on Physics.SE for extended details. Having said that, light is an electromagnetic phenomenon, and as such can be manipulated by Magneto according to canon:
He can also generate electromagnetic pulses of great strength and generate and manipulate electromagnetic energy down to photons. He can turn invisible by warping visible light around his body. - via Wikipedia, with ukltimate source Vision and the Scarlet Witch #4 (February 1983)
The short answer is yes. In the comic-book canon, Magneto demonstrates a wide range of powers that aren't seen in the films including a force-field strong enough to block the she-hulk and the ability to fly (whereas he only has the ability to influence metal in the films).
In "Vision and the Scarlet Witch : Vol 1 #4" we see him 'wrapping himself in a cocoon of metal' which he then uses to bend light around him;
The same cocoon apparently allows him to 'traverse vast distances of empty space' without a space suit.
Sort of. Maybe.
If we assume some semblance of physics as we currently know it, then Magneto cannot "create darkness", because darkness is not a "thing" one "creates". But he could prevent light from entering some space, which would then appear dark to people inside it. Or he could prevent light from leaving some space, which would then appear dark to people outside. Neither of these is quite the same thing as what you asked, but they might achieve similar purposes.
Then again, we're also talking about comic book superheroes. "Physics as we currently know it" may not be a very safe assumption.
Just as Magneto can't control electricity, he can't control light. His abilities are strictly to metal. But he can still use metal to reflect the light.