Insight into the metallurgy of UCoGe by electron-beam zone refining crystal growth*

New insights into the phenomena of superconductivity have been enabled by the recently discovered U-based ferromagnetic superconducting compounds UGe₂, UCoGe, URhGe, and UTe₂. Sample quality in these compounds has proven to be a challenge for achieving a maximal superconducting transition temperature.  

We report the growth and characterization of single crystal UCoGe made by electron-beam floating-zone refining in an ultra-high vacuum environment. Once annealed at 900 C, the zone-refinied UCoGe samples show a well defined superconducting transition at ∽0.55 K and a ferromagnetic transition at ∽2.6 K through both electrical resistivity and heat capacity, consistent with samples grown by other methods. Using scanning electron microscopy we observed a new U-rich phase that collected in cracks and voids within the UCoGe crystal, which may be a key to improving future sample quality.