  Application of an electric stimulus to a material with a metal-insulator
transition can trigger a large resistance change. Resistive switching from an
insulating into a metallic phase, which typically occurs by the formation of
conducting filaments parallel to the current flow, has been an active research
topic. Here we present the discovery of an opposite, metal-to-insulator
switching that proceeds via nucleation and growth of an insulating barrier
perpendicular to the driving current. The barrier formation leads to an unusual
N-type negative differential resistance in the current-voltage characteristics.
Electrically inducing a transverse barrier enables a novel approach to
voltage-controlled magnetism. By triggering a metal-to-insulator resistive
switching in a magnetic material, local on/off control of ferromagnetism can be
achieved by a global voltage bias applied to the whole device.
