Low temperature Terahertz Spectroscopy of LaFeO${}_3$, PrFeO${}_3$, ErFeO${}_3$, and LuFeO${}_3$: Quasimagnon resonances and ground multiplet transitions

Abstract

We report on zone center THz excitations of non-Jahn Teller LaFeO${}_3$, PrFeO${}_3$, ErFeO${}_3$, and LuFeO${}_3$ distorted perovskites under external magnetic fields up 7 T. Low temperature-low energy absorptions of LaFeO${}_3$ show antiferromagnetic and ferromagnetic quasimagnons at $\omega$AFM ~31.4 and $\omega$FM ~26.7 cm${}^{-1}$ in the $\Gamma$4 (Gx, Ay, Fz) representation. LuFeO${}_3$ is characterized by zero field magnetic resonances at $\omega$AFM ~26.3 cm${}^{-1}$ and $\omega$FM ~22.4 cm${}^{-1}$ in addition to Fe${}^{3+}$ Zeeman-split crystal field (CF) 6A${}_1$ ground transitions at ~10.4 cm${}^{-1}$ triggered by structural deviations induced by smaller Lu 4f${}^{14}$. This local non-centrosymmetric departure is also found in ErFeO${}_3$ (Kramers 4f${}^{11}$ Er${}^{3+}$ (4I15/2); Γ2 (Fx, Cy, Gz) <TSR ~93 K), but with the ~4 cm${}^{-1}$ Fe${}^{3+}$ Zeeman branching strongly biased toward higher energies. Quasimagnons at $\omega$AFM ~31.5 cm${}^{-1}$ and $\omega$FM ~21.5 cm${}^{-1}$ in ErFeO${}_3$ do not undergo field induced band splits but a 13-fold increase in the antiferro ($\omega$AMF) /ferro($\omega$AFM) intensity ratio. There is a remarkable field-dependent CF matching population balance between Fe${}^{3+}$ higher and Er${}^{3+}$ lower Zeeman branches. Antiferro- and ferro- resonances in PrFeO${}_3$ turn much broader as non-Kramers Pr${}^3$ introduces ligand changes at the A site leading into near degeneracy the antiferromagnetic mode and the lowest Pr${}^{3+}$ CF transition. We conclude that low energy excitations in RFeO${}_3$ (R=rare earth) strongly depend on the lanthanide ionic size. Minute lattice displacements also underlie considering non-centrosymmetric the most distorted RFeO${}_3$ (R=rare earth). Changes triggered by the smaller rare earth and the nonlinear intrinsic oxygen ion polarizability provide grounds for interplay of ionic and electronic interactions yielding ferroelectric spontaneous polarization.

Full Manuscript and Supplemental Material, 73 pages, 27 figures

References in corpus (7)

• Spin current and magneto-electric effect in non-collinear magnets
• Temporal and spectral fingerprints of ultrafast all-coherent spin switching
• Raman spectroscopy of rare-earth orthoferrites RFeO3 (R = La, Sm, Eu, Gd, Tb, Dy)
• Multiferroic hexagonal ferrites (h-RFeO${}_3$, R=Y, Dy-Lu): an experimental review
• Determination of the exchange anisotropy in perovskite antiferromagnets using powder inelastic neutron scattering
• Lyddane-Sachs-Teller relationship in linear magnetoelectrics
• Spin dynamics and exchange interaction in orthoferrite TbFeO${}_3$ with non-Kramers rare-earth ion

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• Spin-phonon interactions revisited: Far-infrared emission, Raman scattering, and high-resolution x-ray diffraction at the Néel temperature in LaFeO3