Magnetotransport properties of ferromagnetic Ga1-xMnxAs layers on a (100) GaAs substrate.

The magnetotransport properties of ferromagnetic Ga_1-xMn_xAs epilayers with Mn mole fractions in the range of x≈2.2%–4.4% were investigated using Hall effect measurements. The temperature-dependent Hall carrier concentration for a metallic sample with x≈2.2% was analyzed assuming an activation energy from two acceptor levels. It was found that the two acceptor levels with activation energies of 129.4 and 31.6 meV at B=0 Oe decreased to 87.6 and 30.7 meV, respectively, at B=5 kOe. The decrease in acceptor activation energy from 129.6 to 87.6 meV was due to the spin splitting of the Mn acceptor level in the ferromagnetic region, and was responsible for the increase in carrier concentration. From magnetic-field-dependent Hall resistance data, the Curie temperature was estimated to be T_C=60 and 70 K for Ga_1-xMn_xAs samples with x≈2.2 and x≈4.4%, respectively. The magnetoresistance measurements confirmed that the anomalous Hall effect existed in these samples that showed metallic and insulating behavior, respectively. [ABSTRACT FROM AUTHOR]