R. G. Mitarov, S. N. Kallaev, Z. M. Omarov, O. M. Nazarova, L. A. Reznichenko, “Influence of the multiplet levels of Sm$^{3+}$ and Eu$^{3+}$ on the heat capacity of multiferroic BiFeO$_{3}$”, Fizika Tverdogo Tela, 63:6 (2021), 763–766; Phys. Solid State, 63:6 (2021), 877–880
