Ho3+ crystal-field levels, magnetic ordering, and magnetoelastic coupling in the chain nickelate Ho2BaNiO5

• First optical spectroscopic study of Ho2BaNiO5 was done.
• Quasi-doublet ground state of Ho3+ ion was found.
• Magnetostriction driven change of the crystal field energies was observed.
• Ho contribution into the heat capacity and magnetic susceptibility was calculated.

Transmission spectroscopy data in wide spectral and temperature ranges are presented for Ho2BaNiO5. A quasi-doublet ground state of the non-Kramers Ho3+ ion, previously predicted theoretically, is confirmed experimentally for the first time. Its temperature-dependent splitting manifesting magnetic ordering at the Neél temperature TN = 49 K is discussed in the frame of the perturbation and mean-field approaches. Holmium contribution into the magnetic susceptibility χ(T) and specific heat C(T) is calculated using the spectroscopic data. The calculated contribution describes well experimental data available in literature. Analysis of shifts of the Ho3+ energy levels reveals magnetoelastic interactions in the antiferromagnetic state of Ho2BaNiO5.