Investigating the vibrational lattice anisotropy in FeTe_0.5Se_0.5 using magnetically oriented crystallites

An iron chalcogenide sample with nominal composition FeTe_0.5Se_0.5 was synthesized following a solid-state reaction route. X-ray diffraction followed by Rietveld analysis were used for verifying the phase content. Using the field of an 11.7 T magnet textured samples, having the c axes parallel with and normal to the sample surface, were made. ⁵⁷Fe Mössbauer spectroscopy in transmission geometry was used for characterizing the hyperfine parameters of the iron site. Clear indications of vibrational anisotropy, i.e. the Goldanskii-Karyagin effect, were observed. Fitting spectral absorption with the Debye model yielded rather low Debye temperatures of 255(3) and 303(3) K, for samples texturized with the c axis parallel with and perpendicular to the Mössbauer γ beam, respectively. Also the second-order Doppler shift of the isomer shift data exhibited a similar, although weaker, anisotropy.