Effect of annealing on the magnetic and superconducting properties of single-crystalline UCoGe

Abstract Single-crystals of the new ferromagnetic superconductor UCoGe have been grown. The quality of as-grown samples can be significantly improved by a heat-treatment procedure, which increases the residual resistance ratio ( RRR ) from ∼5 to ∼30. Magnetization M ( T ) and resistivity ρ ( T ) measurements show the annealed samples have a sharp ferromagnetic transition with a Curie temperature T C is 2.8 K. The ordered moment of 0.06 μ B is directed along the orthorhombic c -axis. Superconductivity is found below a resistive transition temperature T s =0.65 K.