  Electric-field manipulation of magnetic order has proved of both fundamental
and technological importance in spintronic devices. So far, electric-field
control of ferromagnetism, magnetization and magnetic anisotropy has been
explored in various magnetic materials, but the efficient electric-field
control of spin-orbit torque (SOT) still remains elusive. Here, we report the
effective electric-field control of a giant SOT in a Cr-doped topological
insulator (TI) thin film using a top-gate FET structure. The SOT strength can
be modulated by a factor of 4 within the accessible gate voltage range, and it
shows strong correlation with the spin-polarized surface current in the film.
Furthermore, we demonstrate the magnetization switching by scanning gate
voltage with constant current and in-plane magnetic field applied in the film.
The effective electric-field control of SOT and the giant spin-torque
efficiency in Cr-doped TI may lead to the development of energy-efficient
gate-controlled spin-torque devices compatible with modern field-effect
semiconductor technologies.
