Magnetic interactions in TDAE-C-60

We have introduced the two-channel Sherrington-Kirkpatrick (SK) model to account for the temperature dependency of the magnetization of TDAE-C-60 measured under very small magnetic field of order of 0.1 Oc. The two-channel SK model includes another glassy degree of freedom than spins. The second glassy degree of freedom couples to spins and hence has influence on the magnetic properties. This model is successful in explaining the rapid increase of the field cooling (FC) magnetization in the low-temperature region below the freezing temperature as well as the onset of the remanence, the difference between the FC and zero-field cooling magnetization, found in the experiment, both of which are difficult to explain simultaneously by the standard spin-glass models or ferromagnetic domains. While the phase in the two-channel SK model we found relevant for the experiment is quite different from the standard spin-glass models in the meaning described above, it has a similarity with the mixed phase of the SK model, in the meaning that both the Edward-Anderson order parameter and the spontaneous magnetization have nonzero values. This does not contradict the muon-spin-relaxation experiment, which shows the existence of the spontaneous magnetization in TDAE-C-60. We have also discussed the possible microscopic origin of the second glassy degree of freedom.