Modeling Spectroscopic Properties of Ni2+ Ions in the Haldane Gap System Y2BaNiO5

Abstract

Modeling of spin Hamiltonian parameters enables correlation of crystallographic, spectroscopic, and magnetic data for transition ions in crystals. In this paper, based on the crystallographic data and utilizing the point-charge model and superposition model, the crystal field parameters (CFPs) are estimated for Ni2+(3d8) ions in the Haldane gap system Y2BaNiO5. The CFPs serve as input for the perturbation theory expressions and the crystal field analysis package for microscopic spin Hamiltonian modeling of the zero-field splitting parameters (ZFSPs) D and E. Results of an extensive literature search of the pertinent crystallographic data, experimental ZFSPs, and model parameters are briefly outlined. The modeling aims at verification of the experimental ‘single ion anisotropy’ parameters and explanation of the controversy concerning the maximal rhombic distortion |E/D| ≈1/3 reported for Ni2+ ions in Y2BaNiO5. The preliminary results call for reanalysis of some magnetic studies of the Haldane gap systems.

Tools for magnetostructural correlations for the 3d8(3A2 state) ions at orthorhombic sites: Comparative study with applications to Ni2+ ions in Y2BaNiO5 and Nd2BaNiO5

“…Y 2 BaNiO 5 , are of significant interest in magnetism studies [19][20][21][22]. Serious problems have, however, been encountered [18] concerning validity of the MSH expressions derived by Chen and Zhao [23]. It turns out that the sign of the spin-orbit (SO) coupling parameter (SOCP) ζ has been adopted in [23] for Ni 2 þ ions in an ambiguous way.…”

“…Applications for the Ni 2 þ (3d 8 ) ions with the spin S ¼1 at orthorhombic symmetry sites in Y 2 BaNiO 5 have enabled to relate directly the ZFSPs with the structural parameters and thus to study spectroscopic and magnetic properties [18]. Importantly, the Haldane gap systems, as e.g.…”

“…The CFPs obtained in that way have served as input for the modeling of the ZFSPs D and E for Ni 2 þ ions in Y 2 BaNiO 5 utilizing the MSH expressions [23] and the modified CFA/MSH approach (for references, see, [18]). Since the module MSH available within the package CFA is applicable only for axial symmetry, in order to extract the effective ZFSPs from the physical ZFS energy levels, the microscopic expressions suitable for the orthorhombic ZFSPs have been developed in [18]. This version of the approach (ii) is denoted below as CFA þ MSH to distinguish it from the direct CFA/MSH approach [18].…”

“…To estimate the CFPs based on the knowledge of the crystallographic data, two models have been utilized in [18], i.e. the point-charge model (PCM) and SPM.…”

“…The approaches (i) and (ii) combined with superposition model (SPM) calculations [11][12][13][14] of the CF parameters (CFPs) [15][16][17] have recently been employed [18] as tools to study magnetostructural correlations for 3d 8 ions. Applications for the Ni 2 þ (3d 8 ) ions with the spin S ¼1 at orthorhombic symmetry sites in Y 2 BaNiO 5 have enabled to relate directly the ZFSPs with the structural parameters and thus to study spectroscopic and magnetic properties [18].…”