Spin reorientation inNdFe0.5Mn0.5O3: Neutron scattering andab initiostudy

Abstract

The structural, magnetic, and electronic properties of NdFe0.5Mn0.5O3 have been studied in detail using bulk magnetization, neutron/x-ray diffraction and first principles density functional theory calculations. The material crystallizes in the orthorhombic P bnm structure, where both Mn and Fe occupy the same crystallographic site (4b). Mn/Fe sublattice of the compound orders in to a G-type antiferromagnetic phase close to 250 K where the magnetic structure belongs to Γ1 irreducible representation with spins aligned along the crystallographic b direction. This is unconventional in the sense that most of the orthoferrites and orthochromites order in the Γ4 representation below the Néel temperature.This magnetic structure then undergoes a complete spin reorientation transition with temperature in the range 75 K > ∼ T > ∼ 25 K where the magnetic structure exists as a sum of two irreducible representations (Γ1+Γ2) as seen from neutron diffraction measurements. At 6 K, the magnetic structure belongs entirely to Γ2 representation with spins aligned antiferromagnetically along the crystallographic c direction having a small ferromagnetic component (Fx). The unusual spin reorientation and correlation between magnetic ground state and electronic structure have been investigated using first principles calculations within GGA+U and GGA+U+SO formalisms.

Mixing A -type and G -type B -site antiferromagnetism in AMn1Pajerowski1 2018Phys. Rev. B5020View full textAdd to dashboardCite

“…From the model here, the first transition (TN,1 ≈ 250 -300 K) is then a Fe-Gtype dominated transition and the second transition (TN,2 ≈ 50 K) may be assigned to an Mn-Atype dominated transition. This Mn order parameter for the second phase transition at TN,2 is physically distinct from other posited order parameters: neodymium induced [23] as has been inferred from the TNd ≈ 20 K transition in NdMnO3 [42] and the octahedral rotation induced spin-reorientation native to NdFeO3 between 90 K and 120 K. [49] There are model phase transitions that are not experimentally observed in magnetic neutron diffraction. The extension of these MC results to long-range order in a real material is ambiguous because of the finite simulation size.…”

“…At the highest temperatures, the observation of Γ1 is consistent with manganese spins participating in the Gtype order and dominating the anisotropy with DMn||M ≫ DFe. The second magnetic transition beginning near T = 70 K [23] or T = 40 K [18] may be related to the second transition in the MC simulations. In the simulations, this transition is due to a parameter with A⊥M, but no A-type order is reported for NdMn0.5Fe0.5O3.…”

“…The experimental observation of two phase transitions for NdMn0.5Fe0.5O3 [18,23] can be explained by a co-existence of symmetrically distinct end-member-type superexchange-driven order parameters. From the model here, the first transition (TN,1 ≈ 250 -300 K) is then a Fe-Gtype dominated transition and the second transition (TN,2 ≈ 50 K) may be assigned to an Mn-Atype dominated transition.…”

“…For the intermediate-doped regime, the model is not as well motivated and the comparison is less direct. Neutron diffraction has been reported for NdMn0.5Fe0.5O3, [18,23] As for moment direction, in one report the G-type moment is found to rotate from Γ1 = (AS, GM, CL) at higher temperatures to Γ3 = (FS, CM, GL) at lower temperatures, [23] while the other makes no mention of moment direction at either 290 K or 4.3 K. [18] For both sets of diffractograms, the lowest temperature data show greater intensity on the 011 than the 101 (axes order as S, M, L) and the lowest angle data are then consistent with a linear combination of Γ1 and Γ5. At the highest temperatures, the observation of Γ1 is consistent with manganese spins participating in the Gtype order and dominating the anisotropy with DMn||M ≫ DFe.…”

“…For example, neutron diffraction of NMFO observes mode contributions that are less than a weighted average of the end-members. [18,22,23] Secondary to these experimental observations is the need to understand the magnetic superexchange JMnFe that is expected to exist between Mn 3+ and Fe 3+ in these systems, and to understand how incorporating ions into non-native lattices can affect the magnetics of those ions and of the host lattice. Following this introduction, section II presents the computational frameworks used.…”