  Van der Waals materials provide a versatile toolbox for the emergence of new
quantum phenomena and the fabrication of functional heterostructures. Among
them, the trihalide VI3 stands out for its unique magnetic and structural
landscape. Here we investigate the spin and orbital magnetic degrees of freedom
in the layered ferromagnet VI3 by means of temperature-dependent x-ray
absorption spectroscopy and x-ray magnetic circular and linear dichroism. We
detect localized electronic states and reduced magnetic dimensionality, due to
electronic correlations. We furthermore provide experimental evidence of (a) an
unquenched orbital magnetic moment (up to 0.66(7)) in the ferromagnetic state,
and (b) an instability of the orbital moment in proximity of the spin
reorientation transition. Our results support a coherent picture where
electronic correlations give rise to a strong magnetic anisotropy and a large
orbital moment, and establish VI3 as a prime candidate for the study of orbital
quantum effects.
