Orbital Magnetic Moment of Magnons

In experiments and applications usually the spin magnetic moment of magnons is considered. In this Paper we identify an additional degree of freedom of magnons: an \emph{orbital} magnetic moment brought about by spin-orbit coupling.Our microscopic theory uncovers that spin magnetization ${\vec{M}}^{\mathrm{S}}$ and orbital magnetization ${\vec{M}}^{\mathrm{O}}$ are independent quantities. They are not necessarily collinear; thus, even when the total spin moment is compensated due to antiferromagnetism ($\vec{M}^$\mathrm{S}$ = \vec{0}$),$\vec{M}^$\mathrm{O}$$ may be nonzero. This scenario of orbital weak ferromagnetism is realized in paradigmatic kagome antiferromagnets with Dzyaloshinskii-Moriya interaction. We demonstrate that magnets exhibiting a magnonic orbital moment are omnipresent and propose transport experiments for probing it.