  Controlling magnetism by purely electrical means is a key challenge to better
information technology1. A variety of material systems, including ferromagnetic
(FM) metals2,3,4, FM semiconductors5, multiferroics6,7,8 and magnetoelectric
(ME) materials9,10, have been explored for the electric-field control of
magnetism. The recent discovery of two-dimensional (2D) van der Waals
magnets11,12 has opened a new door for the electrical control of magnetism at
the nanometre scale through a van der Waals heterostructure device platform13.
Here we demonstrate the control of magnetism in bilayer CrI3, an
antiferromagnetic (AFM) semiconductor in its ground state12, by the application
of small gate voltages in field-effect devices and the detection of
magnetization using magnetic circular dichroism (MCD) microscopy. The applied
electric field creates an interlayer potential difference, which results in a
large linear ME effect, whose sign depends on the interlayer AFM order. We also
achieve a complete and reversible electrical switching between the interlayer
AFM and FM states in the vicinity of the interlayer spin-flip transition. The
effect originates from the electric-field dependence of the interlayer exchange
bias.
