We demonstrate a magnetic quantum critical point embedded within the superconducting state of Zn-doped ${\mathrm{CeCoIn}}_5$, revealed by a pronounced peak in the magnetic penetration depth at zero temperature $\lambda (0)$. Using scanning superconducting quantum interference device microscopy, we determine the local superconducting transition temperature $T_{\mathrm{c}}$ and $\lambda (0)$. By parametrizing $\lambda (0)$ in terms of the local $T_{\mathrm{c}}$ rather than nominal Zn substitution, we circumvent the ambiguity caused by doping inhomogeneity and enable a more precise extraction of the critical exponent. The extracted effective exponent exceeds the clean spin-density-wave value, consistent with a disorder-modified quantum critical regime. The enhancement of $\lambda (0)$ reflects the suppression of the superfluid stiffness and is consistent with critical scaling. Our approach provides a route to uncover underlying quantum critical behavior obscured by inhomogeneity in unconventional superconductors.

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• Antiferromagnetism
• Critical exponents
• Kondo effect
• Magnetic susceptibility
• Penetration depth
• Quantum criticality
• Superconducting phase transition
• Vortices in superconductors
• Scanning probe microscopy