Chemical substitution offers an effective route to tune magnetic ordering and magnetocaloric performance in rare-earth (RE) oxides for cryogenic refrigeration. Here, we investigate the structural evolution, magnetic properties, and magnetocaloric effect of polycrystalline zircon-type ${\mathrm{Gd}}_{1-x}{\mathrm{Er}}_x{\mathrm{VO}}_4$ $(x=0, 0.1, 0.25, 0.5, \text{and} 0.75)$. Powder x-ray diffraction confirms that all samples crystallize into the tetragonal zircon structure without detectable impurity phases. Substitution of ${\mathrm{Gd}}^{3+}$ by the smaller ${\mathrm{Er}}^{3+}$ ion produces a systematic lattice contraction and modifies the magnetic behavior of the RE sublattice. The magnetic ordering temperature is suppressed from 3.65(2) K in ${\mathrm{GdVO}}_4$ to 2.76(2) K in ${\mathrm{Gd}}_{0.9}{\mathrm{Er}}_{0.1}{\mathrm{VO}}_4$, accompanied by a weakening of the spin-flop-like field-induced anomaly observed in the parent compound. A low Er concentration correspondingly improves the low-temperature magnetocaloric performance, with ${\mathrm{Gd}}_{0.9}{\mathrm{Er}}_{0.1}{\mathrm{VO}}_4$ exhibiting a maximum magnetic entropy change of 45.1 $\mathrm{J}{\mathrm{kg}}^{-1}{\mathrm{K}}^{-1}$ for ${\mu }_0\mathrm{\Delta }H=7\mathrm{T}$. These results demonstrate that weak Er substitution effectively tunes the competition among exchange interactions, dipolar coupling, and magnetic anisotropy, optimizing the balance between magnetic ordering and available spin entropy in zircon-type RE vanadates, which is crucial for developing efficient cryogenic refrigeration materials.

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• Magnetic order
• Magnetic phase transitions
• Magnetic susceptibility
• Magnetism