A combined experimental and first-principles investigation of the magnetic hyperfine field at dilute Ce impurities in the antiferromagnetic intermetallics ${\mathrm{GdIn}}_3$ and ${\mathrm{TbIn}}_3$ is reported here. Perturbed angular correlation spectroscopy using ${}^{140}\mathrm{Ce}$ probes reveals strongly reduced hyperfine fields of $\sim 13\mathrm{T}$ in both hosts, which are substantially smaller than the free-ion value and even reduced relative to ${\mathrm{CeIn}}_3$. To elucidate the local origin of this suppression, we perform spin-polarized density functional calculations including spin-orbit coupling within supercell models that explicitly account for the antiferromagnetic order. A systematic comparison of local spin-density approximation (LSDA), $\mathrm{LSDA}+U$, and hybrid B3PW91 functionals demonstrates that the hyperfine field at the Ce site is overwhelmingly dominated by the orbital contribution associated with the $4f$ shell, while spin-dipolar and Fermi-contact terms nearly cancel out. Conventional $\mathrm{DFT}+U$ (DFT being density functional approximation) artificially localizes the Ce $4f$ states and strongly overestimates hyperfine field. In contrast, calculations with a hybrid functional with enhanced exact exchange reveal a resonance-like $4f$ spectral weight at the Fermi level, yielding nearly quenched spin moments and hyperfine fields in excellent agreement with the experiment. Analysis of the electronic structure and charge-density redistribution indicates that the reduced lattice volume (from lanthanide contraction) of the ${\mathrm{GdIn}}_3$ and ${\mathrm{TbIn}}_3$ hosts exerts an effective chemical pressure on the Ce impurity comparable to the critical pressure of ${\mathrm{CeIn}}_3$, thereby driving the Ce $4f$ electrons into an intermediate-valence regime. These results establish hyperfine interactions as a sensitive microscopic probe of $4f$ hybridization and demonstrate the importance of beyond-semilocal exchange-correlation functionals for reliable predictions of hyperfine properties in correlated rare-earth materials.

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• Fine & hyperfine structure
• Magnetic interactions
• Antiferromagnets
• Rare-earth alloys
• Density functional calculations
• Time-differential perturbed-angular correlation spectroscopy