INTERPLAY BETWEEN THE MAGNETIC AND TRANSPORT-PROPERTIES IN THE III-V DILUTED MAGNETIC SEMICONDUCTOR GA1-XMNXAS

Using a low-temperature molecular-beam epitaxy growth procedure, Ga1-x MnxAs-a III-V diluted magnetic semiconductor-is obtained with Mn conce ntrations up to x similar to 9%. At a critical temperature T-c (T-c ap proximate to 50 K for x=0.03-0.05), a paramagnetic to ferromagnetic ph ase transition occurs as the result of the interaction between Mn-h co mplexes. Hole transport in these compounds is strongly affected by the antiferromagnetic exchange interaction between holes and Mn 3d spins. A model for the transport behavior both above and below Tc( )is given . Above T-c, all materials exhibit transport behavior which is charact eristic for systems near the metal-insulator transition. Below T-c, du e to the rising spontaneous magnetization, spin-disorder scattering de creases and the relative position of the Fermi level towards the mobil ity edge changes. When the magnetization has reached its saturation va lue (below similar to 10 K) variable-range hopping is the main conduct ion mechanism. The negative magnetoresistance is the result of the exp ansion of the hole wave functions in an applied magnetic field.