Long-range ferromagnetic interaction in Ge1-x Mn x Te with high x

The ferromagnetic properties of Ge1-x Mn x Te with high x (x>0.85) are investigated. Even for high x, carrier-induced ferromagnetism is observed: the spontaneous magnetization and the Curie temperature increase with the hole concentration. The magnetic phase transition from ferromagnetic to paramagnetic is second order. The critical exponents are deduced from the modified Arrott plots and scaling behavior. The exponents are in good agreement with those theoretically for the mean field model, suggesting that the ferromagnetic exchange interaction is of long-range type