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Magnetic phase diagram and cluster glass-like properties of stage-1 graphite intercalated FeCl$_3$

We present a comprehensive investigation of the magnetic properties of stage-1 graphite intercalated FeCl$_3$ using a combination of DC and AC magnetic susceptibility, thermoremanent magnetization and field dependent magnetization measurements. This van der Waals system, with a centrosymmetric honeycomb lattice, combines frustration and disorder, due to intercalation, and may be hosting topologically non-trivial magnetic phases. Our study identifies two magnetic phase transitions at $T_{f1} \approx $ 4.2 K and at $T_{f2} \approx $ 2.7 K. We find that the paramagnetic state, for $T > T_{f1}$, is dominated by short-range ferromagnetic correlations. These build up well above $T_{f1}$ and lead to a significant change in magnetic entropy, which reaches $ΔS_M^{Pk} = $ -5.52 J kg$^{-1}$ K$^{-1}$ at 7 T. Between $T_{f1}$ and $T_{f2}$ we observe slow spin dynamics characteristic of a cluster glass-like state, whereas for $T$ $ < $ $T_{f2}$ our results indicate the onset of a low temperature long range ordered state. The analysis of the experimental results leads to a complex phase diagram, which may serve as a reference for future investigations searching for topological non-trivial phases in this system.