  CeTe3 is a unique platform to investigate the itinerant magnetism in a van
der Waals (vdW) coupled metal. Despite chemical pressure being a promising
route to boost quantum fluctuation in this system, a systematic study on the
chemical pressure effect on Ce3+(4f1) states is absent. Here, we report on the
successful growth of a series of Se doped single crystals of CeTe3. We found a
fluctuation driven exotic magnetic rotation from the usual easy-axis ordering
to an unusual hard-axis ordering. Unlike in localized magnetic systems,
near-critical magnetism can increase itinerancy hand-in-hand with enhancing
fluctuation of magnetism. Thus, seemingly unstable hard-axis ordering emerges
through kinetic energy gain, with the self-consistent observation of enhanced
magnetic fluctuation (disorder). As far as we recognize, this order-by-disorder
process in fermionic system is observed for the first time within vdW
materials. Our finding opens a unique experimental platform for direct
visualization of the rich quasiparticle Fermi surface deformation associated
with the Fermionic order-by-disorder process. Also, the search for emergent
exotic phases by further tuning of quantum fluctuation is suggested as a
promising future challenge.

Strongly Correlated Electrons;Materials Science