Pressure and magnetic field control of the spin reorientation transition in the orthoferrite YbFeO₃

YbFeO₃, a rare-earth orthoferrite, stands out due to its remarkably low spin-reorientation transition (SRT) temperature of approximately 8 K. This property makes it a compelling area of study to explore the interaction between noncollinear magnetism within the iron sublattice and the quasi-one-dimensional XXZ effective S = 1/2 chains of Yb³⁺ moments. We present the magnetic dynamics of YbFeO₃ 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. At ambient pressure and temperatures below the SRT, the zero-field excitation spectrum is dominated by a gapped magnon mode ΔE = 0.84 meV, with dispersion exclusively along the [00L] direction. As the temperature rises above the SRT, a continuum emerges atop the magnon mode due to the increased thermal population of the magnon band. When subjected to a magnetic field, two distinct gapped modes become apparent in the INS spectra, regardless of whether the temperature is above or below the SRT. The SRT transition is clearly observable at lower magnetic fields (B < 1 T) but gradually diminishes at higher field strengths. The application of hydrostatic pressure 2 GPa effectively narrows the transition width (ΔT_SRT) and shifts the SRT to higher magnetic fields (B ≈ 3 T). We explore the impact of this applied pressure within the context of a modified mean-field theory, demonstrating that it influences the fourth-order anisotropy constant near the SRT, thus reducing ΔT_SRT.