Superconductivity of Chromium Alloys

Abstract

The superconducting properties of Cr-Ru, Cr-Rh, and Cr-Ir alloys have been investigated and the transition temperatures have been determined as a function of composition and of valence-electron concentration.The Cr-Ru system contains three superconducting phases all of which have a homogeneity range. A hexagonal close-packed alloy containing 50 at.% Cr has a transition temperature of 1.65\ifmmode^\circ\else\textdegree\fi{}K. The sigmaphase type compound ${\mathrm{Cr}}_{2}$Ru has a transition temperature of 2.0\ifmmode^\circ\else\textdegree\fi{}K and ${\mathrm{Cr}}_{3}$Ru which crystallizes in the $\ensuremath{\beta}\ensuremath{-}W$ type structure becomes superconducting at 3.3\ifmmode^\circ\else\textdegree\fi{}K.The hexagonal close-packed alloys in the Cr-Rh system are superconducting. The transition temperature of an alloy containing 70 at.% Cr is 1.1\ifmmode^\circ\else\textdegree\fi{}K. Weak ferromagnetism was observed in cold-worked hexagonal close-packed alloys containing approximately 60 at.% Cr.There are two superconducting phases in the Cr-Ir system. A hexagonal close-packed alloy containing 72 at.% Cr has a transition temperature of 0.83\ifmmode^\circ\else\textdegree\fi{}K. An alloy with the $\ensuremath{\beta}\ensuremath{-}W$ type structure containing 85 at.% Cr becomes superconducting at 0.77\ifmmode^\circ\else\textdegree\fi{}K.Both superconductivity and ferromagnetism occur in the Cr-Ir system. The critical conditions for the occurrence of both phenomena are discussed.