Ferromagnetic percolation in Mn_xGe_(1-x) dilute magnetic semiconductor

摘要

We have studied the magnetic and magnetotransport properties of Mn-doped Ge grown by molecular-beam epitaxy. This group-IV dilute ferromagnetic semiconductor exhibits two magnetic transitions. An upper critical temperature T*_C(～112K for x～0.05) is evident from the extrapolated Curie-Weiss susceptibility and from the Arrott plot analysis of anomalous Hall effect data. The existence of a lower critical temperature T_C (～12 K for x～0.05) is established from ac susceptibility and magnetotransport data. The data are fully compatible with the existence of bound magnetic polarons or clusters below T*_C which percolate at T_C T*_C.