Ferromagnet-insulator-superconductor

In what follows we should bear in mind that the generation of a diamagnetic metallic state (irrespective of whether it is a superconductor or not) will not be favored by a half-filled band of electrons. Either a Peierls distortion or the generation of an antiferromagnetic insulating state will result, with a ferromagnet being less likely for the reasons discussed. Superconductivity in these materials is in fact only observed if electrons are removed, or (less commonly to date) added to the half-filled band. Considerable effort is underway to theoreti-... 

The manganates have the layered perovskite structure similar to that found in the YBCO superconductor (see Section 7.16). This similarity is particularly interesting and may lead to increased understanding of both types of material. The nature of the interactions in the manganites is complicated. They show a metal-insulator transition and a ferromagnetic-antiferromagnetic transition associated with CMR. 

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