The magnetocaloric effect (MCE) is an inherent characteristic of magnetic materials and is considered a potential mechanism for environmentally friendly magnetic refrigeration. However, research on the MCE has been long absent within the field of two-dimensional (2D) magnets. By employing Landau theory of phase transitions, first-principles calculations, and Monte Carlo simulations, we have demonstrated that the transition from bulk to 2D will reduces the MCE in ${\mathrm{Fe}}_3{\mathrm{GeTe}}_2$ (FGT). Remarkably, the MCE performance of the FGT monolayer can be significantly enhanced through substrate engineering. When 2D FGT is placed on InP(111) and Pb(111) substrates, the maximum $-\mathrm{\Delta }{S}_{\mathrm{m}}$ increases from $3.75\mathrm{J}\mathrm{K}{\mathrm{g}}^{-1}{\mathrm{K}}^{-1}$ to 9.9 and $17.4\mathrm{J}\mathrm{K}{\mathrm{g}}^{-1}{\mathrm{K}}^{-1}$, and the corresponding maximum relative cooling power increases from $150.0\mathrm{J}\mathrm{K}{\mathrm{g}}^{-1}$ to 996 and $3742\mathrm{J}\mathrm{K}{\mathrm{g}}^{-1}$ under an out-of-plane magnetic field of 9 T. These enhancements originate from interfacial charge transfer between FGT and the substrates, which improves the MCE performance by simultaneously optimizing magnetic anisotropy energy and interlayer magnetic coupling strength ($J_1$ and $J_2$). These findings provide a deeper understanding of the dimensionality effect on MCE and identify FGT heterojunctions as promising materials for low-dimensional magnetic refrigeration applications.

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• Ferromagnetism
• Landau theory
• Magnetocaloric effect
• Magnetic refrigeration
• Monolayer films
• First-principles calculations
• Monte Carlo methods