Modeling Spectroscopic Properties of Ni 2+ Ions in the Haldane Gap System Y 2 BaNiO 5
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Appl Magn Reson (2013) 44:899–915 DOI 10.1007/s00723-013-0448-8
Magnetic Resonance
Modeling Spectroscopic Properties of Ni2+ Ions in the Haldane Gap System Y2BaNiO5 C. Rudowicz • P. Gnutek • S. Kimura • M. Ac¸ıkgo¨z Y. Y. Yeung
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Received: 28 December 2012 / Revised: 13 February 2013 / Published online: 31 March 2013 Ó The Author(s) 2013. This article is published with open access at Springerlink.com
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.
C. Rudowicz (&) P. Gnutek Modeling in Spectroscopy Group, Institute of Physics, West Pomeranian University of Technology Szczecin, Al. Piasto´w 17, 70-310 Szczecin, Poland e-mail: [email protected] S. Kimura Institute for Materials Research, Tohoku University, Katahira 2-1-1, Sendai 980-8577, Japan M. Ac¸ıkgo¨z Faculty of Art and Sciences, Bahcesehir University, Besiktas, Istanbul, Turkey Y. Y. Yeung Department of Science and Environmental Studies, Hong Kong Institute of Education, Hong Kong SAR, People’s Republic of China
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1 Introduction The Haldane gap systems exhibit several key features [1–5], namely, (1) integer spin (S = 1, 2) on the transition ions, (2) one-dimensional anisotropic antiferromagnetic (AF) chains, (3) no long range magnetic ordering observed down to very low T; (4) a nonmagnetic ‘‘spin-liquid’’ ground state (singlet) separated from a branch of triplet excitations by a finite energy gap D, so-called Haldane gap, conjectured by Haldane in 1983 [6]. Existence of the Haldane gap in the energy spectrum has profound implications for magnetic and spectroscopic properties of these systems. Importantly, no such gap exists for the half-integer spin systems. Numerous theoretical and experimental studies, including inelastic neutron scattering (INS), magnetization, high-magnetic field and high-frequency electron magnetic resonance (HMF–EMR), have been carried out to confirm Haldane’s conjecture [1–5]. Most of the Haldane gap systems discovered so far [1–5] are based on Ni2? (S = 1) ions and exhibit either orthorhombic (e.g., Y2BaNiO5 [YBNO], Ni(C2H8N2)2NO2(ClO
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