Magnetic ground state of the multiferroic hexagonal LuFeO3

Abstract

The structural, electric, and magnetic properties of bulk hexagonal $\mathrm{LuFe}{\mathrm{O}}_{3}$ are investigated. Single phase hexagonal $\mathrm{LuFe}{\mathrm{O}}_{3}$ has been successfully stabilized in the bulk form without any doping by sol-gel method. The hexagonal crystal structure with $P{6}_{3}cm$ space group has been confirmed by x-ray-diffraction, neutron-diffraction, and Raman spectroscopy study at room temperature. Neutron diffraction confirms the hexagonal phase of $\mathrm{LuFe}{\mathrm{O}}_{3}$ persists down to 6 K. Further, the x-ray photoelectron spectroscopy established the 3+ oxidation state of Fe ions. The temperature-dependent magnetic dc susceptibility, specific heat, and neutron-diffraction studies confirm an antiferromagnetic ordering below the N\'eel temperature $({T}_{\mathrm{N}})\ensuremath{\sim}130\phantom{\rule{0.16em}{0ex}}\mathrm{K}$. Analysis of magnetic neutron-diffraction patterns reveals an in-plane ($ab$-plane) ${120}^{\ensuremath{\circ}}$ antiferromagnetic structure, characterized by a propagation vector $k=(0\phantom{\rule{0.16em}{0ex}}0\phantom{\rule{0.16em}{0ex}}0)$ with an ordered moment of $2.84\phantom{\rule{0.16em}{0ex}}{\ensuremath{\mu}}_{\mathrm{B}}/\mathrm{F}{\mathrm{e}}^{3+}$ at 6 K. The ${120}^{\ensuremath{\circ}}$ antifferomagnetic ordering is further confirmed by spin-orbit coupling density functional theory calculations. The on-site coulomb interaction ($U$) and Hund's parameter $({J}_{H})$ on Fe atoms reproduced the neutron-diffraction ${\mathrm{\ensuremath{\Gamma}}}_{1}$ spin pattern among the Fe atoms. $P\text{\ensuremath{-}}E$ loop measurements at room temperature confirm an intrinsic ferroelectricity of the sample with remnant polarization ${P}_{\mathrm{r}}\ensuremath{\sim}0.18\phantom{\rule{0.16em}{0ex}}\ensuremath{\mu}\mathrm{C}/\mathrm{c}{\mathrm{m}}^{2}$. A clear anomaly in the dielectric data is observed at $\ensuremath{\sim}{T}_{\mathrm{N}}$ revealing the presence of magnetoelectric coupling. A change in the lattice constants at ${T}_{\mathrm{N}}$ has also been found, indicating the presence of a strong magnetoelastic coupling. Thus a coupling between lattice, electric, and magnetic degrees of freedom is established in bulk hexagonal $\mathrm{LuFe}{\mathrm{O}}_{3}$.