A 25Mg, 89Y and 115In solid state MAS NMR study of YT2X and Y(T0.5T′0.5)2X (T/T′ = Pd, Ag, Au; X = Mg, In) Heusler phases

Abstract

Yttrium–transition metal–magnesium (indium) Heusler phases YPd₂Mg, YPd₂In, YAg₂Mg, YAg₂In, YAu₂Mg, and YAu₂In and their quaternary compounds (solid solutions) Y(Pd_0.5Ag_0.5)₂Mg, Y(Pd_0.5Ag_0.5)₂In, Y(Pd_0.5Au_0.5)₂Mg, Y(Pd_0.5Au_0.5)₂In, Y(Ag_0.5Au_0.5)₂Mg and Y(Ag_0.5Au_0.5)₂In were synthesized from the elements in sealed niobium ampoules in a high-frequency furnace or by arc-melting, respectively. All compounds crystallize with the cubic MnCu₂Al type structure (Heusler phase), space group Fmm. The structure of Y(Ag_0.39Au_0.61)₂Mg was refined from single crystal X-ray diffractometer data: a = 689.97(5) pm, wR₂ = 0.0619, 52 F² values, 6 parameters. Magnetic susceptibility measurements show Pauli paramagnetic behavior for all samples. The compounds were investigated by ²⁵Mg, ⁸⁹Y and ¹¹⁵In solid state MAS NMR spectroscopy. Large positive resonance shifts are observed for all nuclei. A review of the present data in the context of literature data on isotypic Heusler phases with Cd and Sn indicates that the ⁸⁹Y shifts show a correlation with the electronegativity of the main group atoms (Mg, Cd, In, Sn). The solid solutions Y(Ag_1−xT_x)₂Mg (x = 0.1, 0.25, 0.33, 0.5; T = Pd, Au) clearly show Vegard-like behavior concerning their lattice parameters, and their main group element resonance shifts arising from spin and orbital contributions are close to the interpolated values of the corresponding end-member compounds.