  Polarization is a fundamental property of waves that refers to the
orientation of the oscillations. It has been widely used to encode information
in photonics and phononics. However, the polarization of spin waves is rarely
used yet in magnonics. The reason for this is that only the right-handed
polarized spin waves can be accommodated in ferromagnets. Here, we report that
stable left-handed polarized spin waves can be introduced into ferromagnets if
a spin-polarized electrical current is presented. The right-handed and
left-handed polarized spin waves coexist when the current density is larger
than a critical value while the system keeps stable. The results are confirmed
by micromagnetic simulations. This work provides new playgrounds to study spin
waves and points to new findings for future experimental studies.
