F. N. Bukhanko and A. F. Bukhanko, Evolution of low-energy magnetic excitations pair spectrum in SmMnO_3+δ, Low Temp. Phys. 47, (2021) [Fiz. Nizk. Temp. 47, 1021-1033, (2021)] DOI: https://doi.org/10.1063/10.0006569.