Pressure control of the spin reorientation transition in the rare-earth orthoferrite YbFeO3

https://doi.org/10.1103/PhysRevB.108.054432

${\mathrm{YbFeO}}_3$ is exceptional among the rare-earth orthoferrites for having the lowest spin-reorientation transition (SRT) temperature, $T_{\mathrm{SRT}}\simeq 8K$, which makes it particularly appealing to examine the interplay between noncollinear magnetism of the Fe sublattice and quasi-one-dimensional XXZ effective $S=1/2$ chains of ${\mathrm{Yb}}^{3+}$ moments. Our paper focuses on the magnetic dynamics of ${\mathrm{YbFeO}}_3$ using inelastic neutron scattering (INS), at temperatures below and above the SRT, under an applied hydrostatic pressure of 2 GPa, and in magnetic fields up to 4 T. The low-energy zero-field excitation spectrum at ambient pressure and temperatures below the SRT is dominated by a gapped magnon mode of the Yb subsystem at 0.84 meV with a dispersion only in the $\left[00L\right]$ direction. Above $T_{\mathrm{SRT}}$, a continuum appears on top of the magnon mode because of temperature population of the magnon band, and the gap decreases to around 0.4 meV. The INS spectra in the magnetic field, both above and below $T_{\mathrm{SRT}}$, are characterized by two well-separated gapped modes. The SRT is clearly visible at low fields $B<1T$, but it gradually disappears at higher magnetic fields. The hydrostatic pressure of $p=2\mathrm{GPa}$ effectively reduces the transition width, $\Delta T_{\mathrm{SRT}}$, and keeps the SRT at higher fields up to $B\simeq 3T$. We discuss the effect of the applied pressure in the frame of the modified mean-field theory and show that in the vicinity of the $T_{\mathrm{SRT}}$ the pressure tunes the fourth-order anisotropy constant that effectively reduces the $\Delta T_{\mathrm{SRT}}$.