Giant magnetoresistance and possible miniband effects in periodic magnetic fields

We have investigated the magnetoresistance (MR) of high mobility, near surface two-dimensional electron gases that are subject to a periodic magnetic field of amplitude up to 0.3 T. The fields are produced by sub-micron arrays of ferromagnetic stripes on the surface of the heterostructures. For small applied external magnetic fields we observe an MR of up to 1500% in applied fields of similar to 100 mT. At low temperatures we observe both commensurability and Shubnikov-de Haas oscillations in the same field range. The SdH oscillations are strongly modulated by the 1D periodic magnetic potential. The observed behaviour is not consistent with semiclassical models. A new type of MR is observed on increasing the amplitude of the modulation. In this case, the MR amplitude increases as T-2. This provides evidence of an electron-electron scattering contribution to the resistivity possibly due to the presence of minibands. (C) 1998 Elsevier Science B.V. All rights reserved.