Crystal Field and Magnetic Ordering in the Haldane-Chain Compound Er2BaNiO5 as Studied by Optical Spectroscopy.

High-resolution absorption spectra of the chain compound Er2BaNiO5 were measured in a wide range of frequencies (6000–20,000 cm −1 ) and temperatures (2.5–300 K). Energies of 38 crystal-field levels of Er 3+ in a paramagnetic Er2BaNiO5 were determined. Exchange splittings of crystal-field levels in the antiferromagnetically ordered state ( TN = 34 K) were measured. Crystal-field calculations were performed and the obtained wave functions were used to calculate the temperature dependence of the magnetic susceptibility to be compared with the detailed experimental dependence measured in this work. © 2004 Elsevier B.V. All rights reserved.