Spin swapping for an exchange magnon spin current

We propose the spin-swapping effect for an exchange magnon spin current in a perpendicularly magnetized ferromagnetic medium with in-plane anisotropy on the surface. The excitation of a magnon current flowing along an in-plane direction with an out-of-plane spin polarization leads to the generation of an exchange spin current propagating along the out-of-plane direction, characterized by an in-plane spin polarization. The resulting exchange magnon spin current can induce an inverse spin Hall voltage of microvolts. The exchange coupling at the interface between regions with different magnetic anisotropies plays a crucial role in generating the spin-swapping effect. This is in contrast to the recently reported spin swapping for an exchange spin current in a canted antiferromagnet due to the Dzyaloshiskii-Moriya interaction.