  Recent advances in van der Waals (vdW) materials have sparked renewed
interest in the impact of dimensionality on magnetic phase transitions. While
ordered magnetic phases have been demonstrated to survive in the
two-dimensional (2D) limit, the quest for a spin-glass with quenched magnetic
disorder in lower dimensions has proven elusive. Here we show evidence of a
spin-glass emerging from randomly distributed Fe atoms in Fe3GeTe2, the first
time such a state has been reported in a vdW material. AC magnetic
susceptibility displays a strong frequency dependence indicative of slow spin
dynamics. Additional distinctive phenomena, including ageing, chaos, and memory
effects, further substantiate the existence of a glassy state. Remarkably, we
find that this state persists even in single-unit-cell thick Fe3GeTe2, thereby
confirming the existence of a 2D spin-glass. The formation of spin-glass states
via intercalation in vdW systems allows for highly tunable spin-glass states
that are otherwise difficult to realize.
