Magnetic structures and magnetic phase transitions in the Mn-doped orthoferrite TbFeO₃ studied by neutron powder diffraction

The magnetic structures and the magnetic phase transitions in the Mn-doped orthoferrite TbFeO₃ studied using neutron powder diffraction are reported. Magnetic phase transitions are identified at T_N^Fe/Mn ≈ 295 K where a paramagnetic-to-antiferromagnetic transition occurs in the Fe/Mn sublattice, T_SR^Fe/Mn ≈ 26 K where a spin-reorientation transition occurs in the Fe/Mn sublattice and T_N^R ≈ 2 K where Tb-ordering starts to manifest. At 295 K, the magnetic structure of the Fe/Mn sublattice in TbFe_0.5Mn_0.5O₃ belongs to the irreducible representation Γ 4 (G_xA_yF_z or Pb′n′m). A mixed-domain structure of (Γ₁+ Γ₄) is found at 250 K which remains stable down to the spin re-orientation transition at T_SR^Fe/Mn ≈ 26 K. Below 26 K and above 250 K, the majority phase (> 80 %) is that of Γ₄. Below 10 K the high-temperature phase Γ₄ remains stable till 2 K. At 2 K, Tb develops a magnetic moment value of 0.6(2) μ_B/f.u. and orders long-range in F_z compatible with the Γ₄ representation. Our study confirms the magnetic phase transitions reported already in a single crystal of TbFe_0.5Mn_0.5O₃ and, in addition, reveals the presence of mixed magnetic domains. The ratio of these magnetic domains as a function of temperature is estimated from Rietveld refinement of neutron diffraction data. Indications of short-range magnetic correlations are present in the low-Q region of the neutron diffraction patterns at T < T_SR^Fe/Mn. These results should motivate further experimental work devoted to measure electric polarization and magnetocapacitance of TbFe_0.5Mn_0.5O₃.