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 μB/atom in a 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 flexoelectronic polarization instead of ferroelectricity. The discovery of a large magnetic moment in silicon may enable the use of nonmagnetic and nonferroelectric semiconductors in various multiferroic and spintronic applications.
Keywords: dynamical multiferroicity; flexoelectronic; phonon magnetic moment; silicon.