  Spin transistors (whose on-off operation is achieved by
electric-field-controlled spin orientation 1), if realized, can revolutionize
modern electronics through the implementation of a faster and a more
energy-efficient performance as well as non-volatile data storage 2, 3. The
original proposal by Datta and Das 1 that relies on electric-field-controlled
spin precession in a semiconductor channel faces significant challenges
including inefficient spin injection, spin relaxation and spread of the spin
precession angle 4, 5. Recent demonstration of electric-field switching of
magnetic order 6-8 and spin filtering 9-12 in two-dimensional magnetic
insulator CrI3 has inspired a new operational principle for spin transistors.
Here we demonstrate spin field-effect transistors based on dual-gated
graphene/CrI3 tunnel junctions. These devices show an ambipolar transistor
behavior and tunnel magnetoresistance widely tunable by gating when the CrI3
magnetic tunnel barrier undergoes an antiferromagnetic-ferromagnetic spin-flip
transition. Under a constant magnetic bias in the vicinity of the spin-flip
transition, the gate voltage can repeatedly alter the device between a high and
a low conductance state with a large hysteresis. This new spin transistor
concept based on the electric-field-controlled spin-flip transition in the
magnetic tunnel barrier is immune to interface imperfections and allows spin
injection, control and detection in a single device.
