Critical behaviour of coupled organic ferromagnet chains

The interchain coupling in a model, which is most relevant to organic ferromagnets, is studied by a kind of mean field theory. A full phase diagram is given for this model. It is shown that the interchain coupling dramatically affects the ferromagnetic order in the ground state. When the interchain coupling reaches a critical value, the high-spin ground state disappears and the system may transit from ferromagnetic phase into Kondo-singlet phase.