Why did the material at the center of earth's core congregate there during the creation of the solar system? Would those certain materials have a tendency to rotate around the early sun in the planet's development for a certain reason?

I would need some help. I am looking for an article concerning creating an electromagnetic field by a rotating metal. In this article is mentioned, that the effect was much higher than expected. Also Einstein is mentioned. While Einstein described this effect as negligible, the study achieved a higher value. Does anybody know, where i can find this article?