  Magnetic layered van der Waals crystals are an emerging class of materials
giving access to new physical phenomena, as illustrated by the recent
observation of 2D ferromagnetism in Cr2Ge2Te6 and CrI3. Of particular interest
in semiconductors is the interplay between magnetism and transport, which has
remained unexplored. Here we report first magneto-transport measurements on
exfoliated CrI3 crystals. We find that tunneling conduction in the direction
perpendicular to the crystalline planes exhibits a magnetoresistance as large
as 10 000 %. The evolution of the magnetoresistance with magnetic field and
temperature reveals that the phenomenon originates from multiple transitions to
different magnetic states, whose possible microscopic nature is discussed on
the basis of all existing experimental observations. This observed dependence
of the conductance of a tunnel barrier on its magnetic state is a new
phenomenon that demonstrates the presence of a strong coupling between
transport and magnetism in magnetic van der Waals semiconductors.
