A comprehensive structural and microstructural investigation of a new iron-telluride nano phase

A nanocrystalline iron-rich telluride, Fe5Te4, was prepared mechanochemically using ball milling procedures in an inert atmosphere, starting from FexTe powder mixtures with x = 1.0, 1.25 and 1.5, with x = 1.25 leading to the pure phase. Its crystal structure has a tetragonal (I4/m) symmetry and shows an anomalously short Fe-Fe interaction of 2.52 angstrom. The microstructure of the nanocrystalline material was deeply studied by synchrotron X-ray total scattering techniques and the Debye scattering equation (DSE) method. A DSE-based microstrain model, integrated with structure, size and morphology information, indicates the presence of highly strained nanoparticles, with strain more preferentially accumulated in the ab-plane than along the c-axis of the tetragonal structure. Magnetic and Mossbauer spectroscopic characterization indicates that the samples present a spin glass state below the freezing temperature (ca. 150 K) and a magnetic behavior dependent on the applied field, showing ferromagnetic-like loops and a superparamagnetic-like increase of magnetization up to the maximum applied field of 90 kOe.