Structural disorder and magnetism in rare-earth (R) R117Co54+xSn112±y

Abstract

The cubic R117Co54+xSn112±y compounds (R=La–Lu, except Pm, Eu, and Yb) have been synthesized and characterized using X-ray diffraction and magnetization measurements. The existence of the compounds with R=Ce, Pr, Sm, Gd, Tb, and Dy has been confirmed, while new compounds with R=Y, La, Nd, Ho, Er, Tm, and Lu have been discovered. All of the studied phases adopt the Dy117Co57Sn112-type crystal structures with a giant cubic cell (a∼30Å) when the proper heat treatment regime was selected. The lattice parameter decreases from La to Lu, in accordance with the lanthanide contraction and indicating the trivalent state for Ce in Ce117Co54.5Sn115.2. The Co/Sn compositional ratio increases when the size of the R atoms decreases. A single crystal investigation of Gd117Co56.4Sn114.3 confirms extensive structural disorder, particularly around the (1/2,1/2,1/2) location of the unit cell (4b site). Such disorder leads to an elongation of the thermal ellipsoids for the atoms surrounding this location. The magnetic measurements of the compounds with R=Ce, Gd and Tb indicate weak magnetic interactions and non-collinear alignment of magnetic moments in the ordered state. The electrical resistivity of Gd117Co56.4Sn114.3 shows interesting behavior with a change of sign at TC for the dρ/dT parameter.