57Fe Mössbauer Spectroscopy Study of SmFe3 – xAlx(BO3)4 (x = 0–0.28) Multiferroics

Abstract

SmFe_{3 – x}Al_x(BO₃)₄ multiferroic single crystals with x = 0–0.28 have been studied in the temperature range T = 3.8−298 K using ⁵⁷Fe Mössbauer spectroscopy and X-ray diffraction analysis. An increase in the Mössbauer hyperfine quadrupole splitting with the content of aluminum x impurities has been found. For all studied samples, the Mössbauer Debye temperatures Θ_M of iron ions have been determined in good agreement with the values for iron ions calculated from X-ray diffraction data. It has been shown that the low-temperature Mössbauer spectral lines of single crystals doped with Al in a magnetically ordered state are broadened compared to the corresponding lines of the undoped SmFe₃(BO₃)₄ ferroborate; this broadening is best approximated within the multilevel spin relaxation model. The Néel temperatures T_N of the magnetic phase transition have been determined for all studied SmFe_{3 – x}Al_x(BO₃)₄ samples. It has been (found that the Néel temperature T_N decreases nonlinearly with an increase in the content x of aluminum, and the type of three-dimensional magnetic ordering changes from planar to Ising.