  Two-dimensional (2D) van der Waals (vdW) ferromagnets have opened new avenues
for manipulating spin at the limits of single or few atomic layers, and for
creating unique magneto-exciton devices through the coupling of long-range
ferromagnetic (FM) orders and excitons. However, 2D vdW ferromagnets explored
so far have rarely possessed exciton behaviors; to date, FM CrI3 have been
recently revealed to show ligand-field photoluminescence correlated with FM
ordering, but typically with a broad emission peak. Alternatively, many-body
excitons have been observed in antiferromagnetic (AFM) NiPS3, but the coupling
of excitons with AFM orders is exponentially more difficult, owing to extremely
high coercivity. Here, we report a straightforward approach to realize strong
coupling of narrow helical emission and FM orders at a low magnetic field in
CrI3 through a relatively simple microsphere cavity. We show that the resonant
whispering-gallery-modes (WGM) of SiO2 microspheres give rising to a series of
strong oscillation helical emissions with a full width at half-maximum (FWHM)
of ~5 nm under continuous wave excitation. Reversible magnetic control and
coding of helical luminescence with multiwavelength is realized in the range of
950-1100 nm. This work enables plenty of opportunities for creating magnetic
encoding lasing for photonic integrated chips.
