Magnetic and transport properties of Ga_1-xMn_xAs, a new III-V diluted magnetic semiconductor

摘要

Ga_1-xMn_xAs is a new III-V diluted magnetic semiconductor that can be grown by MBE with Mn concentrations up to x approx approx 0.09. Below a critical temperature T_c, determined by the Mn concentration (about 50 K for x=0.05) the material becomesferromagnetic. This is attributed to the magnetic long-range order of Mn-hole complexes, the latter being the result of the strong antiferromagnetic interaction between the holes and Mn 3d spins. Transport and magnetic propertiesof the Ga_1-xMn_xAs system are strongly correlated. Above T_c, all samples show transport behaviour characteristic for materials near the metal insulator transition. Below T_c, resistivity decreases as the magnetic ordering sets in. When the magnetisation has reached its saturation value (below approx 20 K), variable range hopping is the main transport mechanism. Also, a negative magnetoresistance is observed below T_c.