Tricritical behavior of the two-dimensional intrinsically ferromagnetic semiconductor CrGeTe3

${\mathrm{CrGeTe}}_{3}$ recently emerges as a new two-dimensional (2D) ferromagnetic semiconductor that is promising for spintronic device applications. Unlike ${\mathrm{CrSiTe}}_{3}$ whose magnetism can be understood using the 2D-Ising model, ${\mathrm{CrGeTe}}_{3}$ exhibits a smaller van der Waals gap and larger cleavage energy, which could lead to a transition of magnetic mechanism from 2D to 3D. To confirm this speculation, we investigate the critical behavior of ${\mathrm{CrGeTe}}_{3}$ around the second-order paramagnetic-ferromagnetic phase transition. We obtain the critical exponents estimated by several common experimental techniques including the modified Arrott plot, Kouvel-Fisher method, and critical isotherm analysis, which show that the magnetism of ${\mathrm{CrGeTe}}_{3}$ follows the tricritical mean-field model with the critical exponents $\ensuremath{\beta}$, $\ensuremath{\gamma}$, and $\ensuremath{\delta}$ of $0.240\ifmmode\pm\else\textpm\fi{}0.006$, $1.000\ifmmode\pm\else\textpm\fi{}0.005$, and $5.070\ifmmode\pm\else\textpm\fi{}0.006$, respectively, at the Curie temperature of 67.9 K. We therefore suggest that the magnetic phase transition from 2D to 3D for ${\mathrm{CrGeTe}}_{3}$ should locate near a tricritical point. Our experiment provides a direct demonstration of the applicability of the tricritical mean-field model to a 2D ferromagnetic semiconductor.