  Tuning magnetic properties in layered van der Waals (vdW) materials has
captured a significant attention due to the efficient control of ground-states
by heterostructuring and external stimuli. Electron doping by electrostatic
gating, interfacial charge transfer and intercalation is particularly effective
in manipulating the exchange and spin-orbit properties, resulting in a control
of Curie temperature ($T_{\text{C}}$) and magnetic anisotropy. Here, we
discover an uncharted role of intercalation to generate magnetic frustration.
As a model study, we intercalate Na atoms into the vdW gaps of pristine
Cr$_2$Ge$_2$Te$_6$ (CGT) where generated magnetic frustration leads to emerging
spin-glass states coexisting with a ferromagnetic order. A series of dynamic
magnetic susceptibility measurements/analysis confirms the formation of
magnetic clusters representing slow dynamics with a distribution of relaxation
times. The intercalation also modifies other macroscopic physical parameters
including the significant enhancement of $T_{\text{C}}$ from 66\,K to 240\,K
and the switching of magnetic easy-hard axis direction. Our study identifies
intercalation as a unique route to generate emerging frustrated spin states in
simple vdW crystals.
