Grain boundaries are critical for determining the functionality of polycrystalline materials. Here we investigate and present the structural and transport properties of grain boundaries in the unconventional superconductor ${\mathrm{CeCoIn}}_5$. We provide a detailed recipe for the fabrication of isolated grain-boundary devices from as-grown polycrystalline samples of ${\mathrm{CeCoIn}}_5$. Electron backscattered diffraction imaging of polycrystalline ${\mathrm{CeCoIn}}_5$ samples reveals an abundance of ${90}^{\circ }$ misorientation grain boundaries, suggesting a preferential nucleation of ${\mathrm{CeCoIn}}_5$ grains with ${90}^{\circ }$ misorientation over a random distribution of grain orientations. Transport measurements across grain-boundary devices establish coherence of superconductivity and allow us to establish a lower bound on the critical current density for the grain boundaries. Our work opens possibilities for fabrication of quantum devices such as Josephson junctions out of bulk unconventional superconducting materials.

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• Grain boundaries
• Superconductivity
• Heavy-fermion systems
• Superconducting devices
• Unconventional superconductors
• Electron microscopy
• Focused ion beam