Yes. Urobuchi said that he's a big fan of Steins;Gate.
And in my opinion, I don't like Madoka Magica because it's filling up with troll contents. It's nothing but OTAKU magnet.
Nevertheless, I don't want to say that Madoka Magica is ripoff, easily. Because a novel which has time travel factor is existed from about 300 years ago.
Well, even if it's no problem officially because Urobuchi is a member of Nitro+, they should've made Madoka Magica later.
Either way, it's obvious that Steins;Gate is one of the most elaborated story about time travel and Madoka Magica is
not original anime series, definitely.
Oh, and I don't know "attractor field theory" is really correct as the term. Because there is a Japanese version only.