  The magnetic and dielectric properties of \aa kermanite Sr$_2$CoSi$_2$O$_7$
single crystals in high magnetic fields were investigated. We have observed
finite induced electric polarization along the c axis in high fields, wherein
all Co spins were forcibly aligned to the magnetic field direction. Existence
of the induced polarization in the spin-polarized state accompanied with the
finite slope in the magnetization curve suggests the possible role of the
orbital angular momenta in the excited states as its microscopic origin. The
emergence of the field-induced polarization without particular magnetic order
can be regarded as the magnetoelectric effects of the second order from the
symmetry point of view. A low magnetic field-driven electric polarization flip
induced by a rotating field, even at room temperature, has been successfully
demonstrated.
