Structural, hyperfine, and magnetic properties of R2FeTaO7 compounds (R=Y, Dy, Gd, and Eu)

Pyrochlore-related compounds of the ${R}_{2}{\text{FeTaO}}_{7}$ type (with $R=\text{Gd}$, Eu, Dy, and Y) were synthesized by solid-state reaction of precursor oxides. The compounds were structurally and magnetically characterized by x-ray diffraction, M\"ossbauer spectroscopy, and magnetic measurements. The results revealed that this subfamily of pyrochlores crystallizes with the $\mathbf{R}\overline{\mathbf{3}}$ symmetry, where iron with tantalum occupies two different crystallographic sites. Magnetic phase transition to a long-range ordered state was not observed down to 2 K, although islands of magnetically oriented iron atoms could be detected.