²⁷Al and ⁴⁵Sc NMR Spectroscopy on Sc<i>T</i>₂Al and Sc(<i>T</i>_0.5<i>T′</i>_0.5)₂Al (<i>T</i> = <i>T′</i> = Ni, Pd, Pt, Cu, Ag, Au) <i>Heusler</i> Phases and Superconductivity in Sc(Pd_0.5Au_0.5)₂Al

Abstract

Abstract The intermetallic Heusler compounds with Sc T 2 Al and Sc( T 0.5 T′ 0.5 ) 2 Al composition with T = T' = Ni, Pd, Pt, Cu, Ag, Au were synthesized from the elements by arc melting. They crystallize in the cubic MnCu 2 Al type structure, space group Fm $\bar{3}$ m . The unit cell parameters were determined by powder X‐ray diffraction and the structure of Sc(Pd 0.5 Au 0.5 ) 2 Al was refined on the basis of single‐crystal X‐ray diffraction. While the majority of the compounds show Pauli‐paramagnetism, ScAu 2 Al and the newly synthesized solid solution Sc(Pd 0.5 Au 0.5 ) 2 Al exhibit superconductivity with transition temperatures of T C = 4.4 K and T C = 3.0(1) K, respectively. The superconducting state of Sc(Pd 0.5 Au 0.5 ) 2 Al was also investigated by electrical resistivity measurements. All the synthesized compounds were furthermore studied by 27 Al and 45 Sc MAS‐NMR spectroscopy. The resonance shifts of the synthesized compounds were determined and in Sc(Pd 1– x Au x ) 2 Al a linear relationship between the resonance shifts and the composition was found. Line broadening effects and enhanced quadrupolar interaction strengths observed in the mixed samples can be attributed to the effect of Pd/Au mixing on the 8 c Wyckoff site. The NMR spectroscopic data give no clear evidence for or against Sc/Al site disordering.