Spin dynamics and exchange interaction in orthoferrite TbFeO3 with non-Kramers rare-earth ion

The low-temperature spin dynamics of the orthorhombic ${\mathrm{TbFeO}}₃$ perovskite has been studied. It has been found that the inelastic neutron scattering (INS) spectrum of the investigated compound contains two modes corresponding to different sublattices. It is shown that the iron subsystem orders antiferromagnetically at ${T}_{\text{N}}=632$ K and exhibits the high-energy magnon dispersion. The magnetic dynamics of this subsystem has been described within the linear spin wave theory and the in-plane and out-of-plane exchange anisotropy has been demonstrated. The approach proposed previously to describe the magnon dispersion in the ${\mathrm{TmFeO}}₃$ compound has been used. Three levels of the nondispersive crystal electric field corresponding to ${\mathrm{Tb}}³⁺$ ions have been found in the energy region below 40 meV at about 17, 26, and 35 meV. The behavior of the magnetic correlation length of the terbium subsystem has been determined by studying the diffuse scattering at different temperatures. The evolution of this subsystem has been numerically described within the point charge model. It is shown that the numerical data agree satisfactorily with the experiment and with the general concept of the single-ion approximation applied to the rare-earth subsystem of orthorhombic perovskites.