  Time-dependent rotational electric polarizations have been proposed to
generate temporally varying magnetic moments, for example, through a
combination of ferroelectric polarization and optical phonons. This phenomenon
has been called dynamical multiferroicity, but explicit experimental
demonstrations have been elusive to date. Here, we report the detection of a
temporal magnetic moment as high as 1.2 mu_B/atom in charge-doped thin film of
silicon under flexural strain. We demonstrate that the magnetic moment is
generated by a combination of electric polarization arising from a
flexoelectronic charge separation along the strain gradient and the deformation
potential of phonons. The effect can be controlled by adjusting the external
strain gradient, doping concentration and dopant, and can be regarded as a
dynamical multiferroic effect involving flexoelectronics polarization instead
of ferroelectricity. The discovery of a large magnetic moment in silicon may
enable the use of non-magnetic and non-ferroelectric semiconductors in various
multiferroic and spintronic applications.
