QUANTUM TRANSPORT IN FERROMAGNETIC DOT STRUCTURE EMBEDDED IN SEMICONDUCTOR QUANTUM WIRES

We have made a ferromagnetic-(Ni) dot structure embedded in split-gate quantum wires on AlGaAs/lnGaAs/GaAs pseudmorphic high electron mobili ty transistor (PM-HEMT) by two-step surface modification with scanning tunneling microscope (STM). In low-temperature transport measurements , we observed interesting two magnetization-dependent features. First, aperiodic conductance oscillations were observed against gate voltage before magnetization, while periodic and reproducible oscillations we re recorded after magnetization. Second, in the current-voltage charac teristic, we observed a variation of the Coulomb gap width depending o n whether the magnetic held was applied or not. The gap width with +/- 5000 G application decreases down to less than half width 0 G. To con sider the origin of those transport features, magnetic force microscop y (MFM) measurements have been performed for the embedded Ni dot sampl es. In some cases, we found the domain wall formation inside the dot b efore magnetization. It disappeared after magnetization, which implies a single-domain formation in the entire dot. The domain wall formatio n in the dot are closely related to the transport results. (C) 1998 El sevier Science B.V. All rights reserved.