Effect of Transition Metal Substitution on the Structure and Properties of a Clathrate-Like Compound Eu₇Cu 44 As 23

A series of substitutional solid solutions-Eu₇Cu T As (T = Fe, Co, Ni)-based on a recently discovered clathrate-like compound (Eu₇Cu As ) were synthesized from the elements at 800 °C. Almost up to 50% of Cu can be substituted by Ni, resulting in a linear decrease of the cubic unit cell parameter from = 16.6707(1) Å for the ternary compound to = 16.3719(1) Å for the sample with the nominal composition Eu₇Cu Ni As . In contrast, Co and Fe can only substitute less than 20% of Cu. Crystal structures of six samples of different composition were refined from powder diffraction data. Despite very small differences in scattering powers of Cu, Ni, Co, and Fe, we were able to propose a reasonable model of dopant distribution over copper sites based on the trends in interatomic distances as well as on Mössbauer spectra for the iron-substituted compound Eu₇Cu Fe₈As . Ni doping increases the Curie temperature to 25 K with respect to the parent compound, which is ferromagnetically ordered below 17.5 K, whereas Fe doping suppresses the ferromagnetic ordering in the Eu sublattice.