High-resolution spectral study ofEr3+crystal-field levels and magnetic ordering in(ErxY1−x)2BaNiO5chain compounds

Abstract

A family of linear chain nickelates $({\mathrm{Er}}_{x}{\mathrm{Y}}_{1\ensuremath{-}x}{)}_{2}{\mathrm{BaNiO}}_{5}$ $(x=1,$ 0.8, 0.6, 0.4, 0.2, and 0.1) was studied by high-resolution spectroscopy of the ${\mathrm{Er}}^{3+}$ ion. Energies of 38 crystal-field levels of ${\mathrm{Er}}^{3+}$ and exchange splittings for most of them in a magnetically ordered state were measured. Composition-dependent N\'eel temperatures were found. Crystal-field calculations were performed starting from the analysis in the framework of the exchange-charge model. The wave functions found were used to calculate magnetic $g$ factors for crystal-field levels of ${\mathrm{Er}}^{3+}$ and the magnetic susceptibility $\ensuremath{\chi}(T)$ of the concentrared $x=1$ compound. The latter was compared to the detailed $\ensuremath{\chi}(T)$ curve $(2.0\mathrm{K}<T<300\mathrm{K})$ measured for the ${\mathrm{Er}}_{2}{\mathrm{BaNiO}}_{5}$ powdered sample. From the experimentally measured temperature dependences for the ground-state splittings in the compounds with different composition, we derive, within the molecular-field approximation, the ordered magnetic moments of the nickel and erbium subsystems as functions of temperature and concentration of erbium ions, and plot the staggered magnetization function of nickel chains for a staggered magnetic field along the chain direction.