Suppression of electron channelling in microscopic magnetic waveguides

We investigate the magnetoresistance of two-dimensional electrons confined by a strong gradient of magnetic field in a hybrid semiconductor/ferromagnet structure. Ferromagnets with increasingly large saturation magnetization are used to systematically study the dependence of the recently reported resistance resonance peak [Nogaret et al., Phys. Rev. Lett. 84, 2231 (2000)] on the amplitude of the magnetic modulation. We report the collapse of snake orbit channelling at the Curie temperature of dysprosium while above T-c, a weaker structure is observed that is well explained by the magnetic properties of helical dysprosium. These results allow us to identify two separate contributions in the magnetoresistance: one arising from 2D electrons magnetically confined in snake orbits and a second one, much weaker, arising from the field dependence of the magnetization.