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 mobility 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 were recorded after magnetization. Second, in the current-voltage characteristic, we observed a variation of the Coulomb gap width depending on whether the magnetic field was applied or not. The gap width with +/- 5000 G application decreases down to less than half width 0 G. To consider the origin of those transport features, magnetic force microscopy (MFM) measurements have been performed for the embedded Ni dot samples. In some cases, we found the domain wall formation inside the dot before magnetization. It disappeared after magnetization, which implies a single-domain formation in the entire dot. The domain wall formation in the dot are closely related to the transport results. (C) 1998 Elsevier Science B.V. All rights reserved.