Orientational Order in A3C60: Antiferromagnetic Ising Model for the fcc Lattice

I.I. Mazin, A.I. Liechtenstein, O. Gunnarsson, O.K. Andersen, V.P. Antropov, and S.E. Burkov
Max-Planck-Institut für Festkörperforschung, Stuttgart

By analysis of the electronic contribution to the binding in A3C60, we show that the problem of orientational ordering can be mapped onto the fcc nearest-neighbor antiferromagnetic Ising model with J at the order of 100 K. For T<1.76J, the system should be found in a state which is antiferromagnetically ordered in two dimensions and disordered in the third. This is not inconsistent with present x-ray powder data. We find that the low temperature conduction-band structure closely resembles that of the simplest antiferromagnetically ordered (so-called bidirectional) crystal.

Phys. Rev. Lett. 70, 4142 (1993).

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