Transition from ferromagnetic insulator

T12MU207, while not a GFM, is remarkable in that it shows a transition from an insulating to a ferromagnetic, metallic state at 121Shortly after this report, CMR was discovered in this material, which was shown to contain only Mn" + and, thus, the mechanism must be very different from that causing CMR in the perovskite manganates. This mechanism is still not well understood. 

Fig. 13.3. The phase diagram of Ao.33A o.67Mn03 (A = divalent cation, A = rare earth) as a function of temperature and the global instability index of the idealized perovskite structure. The points show the observed transition temperatures in various compounds. FMM = ferromagnetic metal, PMI = paramagnetic insulator, FMI = ferromagnetic insulator (from Rao et al. 1998).

Fig. 8 Variation of the ferromagnetic Tc or the metal-insulator transition temperature, Tim, in Lnj.xAxMn03 with weighted average radius of the A site cations, [from Rao (reproduced with permission from ref. 8)].

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