Temperature and pressure manipulation of magnetic ordering and phonon dynamics with phase transition in multiferroic ${\mathrm{GdFeO}}_3$: Evidence from Raman scattering

We systematically investigate the detailed dynamics of the phonon and local structure of rare-earth orthoferrites ${\mathrm{GdFeO}}_3$ single crystal with temperature and pressure induced structural/magnetic phase transition by Raman spectroscopy. Phonon evolution related to the motion of octahedra reveals paramagnetic to antiferromagnetic ordering transition of ${\mathrm{Fe}}^{3+}$ ions at Néel temperature $T_{N,Fe}$. By quantifying the polarized Raman spectra, especially the cross-polarized geometry, the lattice dynamics and distortion with local structure rearrangement during ferromagnetic transition has been also discovered. Particularly, we claim that the depolarization ratio could be quantified and used to precisely determine ferromagnetic phase transition of ${\mathrm{GdFeO}}_3$ and symmetry evolution simultaneously. Additionally, pressure dependence (up to 25.03 GPa) of collective phonon behavior indicates that antiphase tilt in ${\mathrm{FeO}}_6$ octahedra is more susceptible to the stress field than the in-phase one. The ${\mathrm{FeO}}_6$ octahedra presents better compressible than ${\mathrm{GdO}}_{12}$ dodecahedra in the ${\mathrm{GdFeO}}_3$ lattice with respect to pressure. This work has discovered the physical mechanism underlying variation of local structural symmetry, octahedra tilt, and phonon dynamics in ${\mathrm{GdFeO}}_3$, which can be regarded as the basic view for a series of ${\mathrm{GdFeO}}_3$-type perovskites and more R${\mathrm{FeO}}_3$ system.

Figure 1

(a) The front view and (b) 3D view of orthorhombic perovskite structure of ${\mathrm{GdFeO}}_3$ with Pnma symmetry. (c) Schematics of ${\mathrm{Fe}}^{3+}$ spins structure for G-type antiferromagnetic ordering at Néel temperature.

Figure 2

Temperature dependence of unpolarized Raman spectra of ${\mathrm{GdFeO}}_3$ and the corresponding Lorentzian fitting.

Figure 3

The thermal evolution of phonon frequency for various vibrational modes and the red solid lines are the fitting curves based on the anharmonic model.

Figure 4

(a) The VV-mode and VH-mode Raman spectra for ${\mathrm{GdFeO}}_3$ at room temperature. (b) Temperature dependence of polarized Raman scattering in VV geometry. (c) The thermal evolution of phonon frequency in the VV and VH geometry for various phonon modes of $A_g$(2), $B_{2g}$(5), $A_g$(5), and $A_g$(7), respectively.

Figure 5

Temperature dependence of (a) the normalized intensity and (b) depolarization ratio of polarized scattering for $A_g$(2), $B_{2g}$(5), $A_g$(7), and $B_{2g}$(1) modes, respectively.

Figure 6

Pressure dependence of Raman spectra observed at room temperature within the pressure range of 0.11–25.03 GPa.

Figure 7

(a) Pressure dependence of phonon frequency and intensity of $B_{1g}$(3) and $A_g$(4) mode. The red solid lines are linear fittings. (b) The pressure coefficients for each vibrational mode. (c) and (d) Schematic representations of vibrations of in-phase tilt and antiphase tilt.