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 TNFe/Mn ≈ 295 K where a paramagnetic-to-antiferromagnetic transition occurs in the Fe/Mn sublattice, TSRFe/Mn ≈ 26 K where a spin-reorientation transition occurs in the Fe/Mn sublattice and TNR ≈ 2 K where Tb-ordering starts to manifest. At 295 K, the magnetic structure of the Fe/Mn sublattice in TbFe0.5Mn0.5O3 belongs to the irreducible representation Γ 4 (GxAyFz 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 TSRFe/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) μB/f.u. and orders long-range in Fz compatible with the Γ4 representation. Our study confirms the magnetic phase transitions reported already in a single crystal of TbFe0.5Mn0.5O3 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 < TSRFe/Mn. These results should motivate further experimental work devoted to measure electric polarization and magnetocapacitance of TbFe0.5Mn0.5O3.