Superconductivity in La-Y-Mn Alloys

Abstract

Crystal structure changes occur along many of the lanthanide compound series, such as between adjacent lanthanide compounds, or a single compound which exhibits polymorphic forms. Since superconductivity is sometimes associated with lattice instabilities, one or both compounds at the structure change might be expected to be superconducting if they have no unpaired 4f electrons. For systems where the particular La compound does not form, or where it is several atomic numbers removed from such an instability, the proper proportions of La and Y or La and Lu can be alloyed to form the pseudo-lanthanide compound. The system investigated was RMn_a, which exhibits a structure change between hexagonal C14 and cubic C15 Laves phases. The C14 phase exists for Nd, Pr, Sm, Lu and Ho to Tm, the Ci5 phase exists for Sm and Gd to Ho, while no RMn_a compounds form in the La, Ce, Eu and Yb systems. Sm and Ho are polymorphic. Samples of La_1−xY_xMn_a, 0.2 ≤ × ≤ 1.0 were prepared by arc melting and subsequent heat treatment. X-ray diffraction powder patterns, metallography, magnetic susceptibility and low temperature heat capacity measurements were made. All alloys contained at least two phases, with the C15 structure predominate for x ≥ 0,6.