VERIFICATION OF ZERO-FIELD SPLITTING THEORY FOR SPIN S = 2 IONS IN MAGNETIC INSULATORS

Relations are derived by computer for spin Hamiltonian parameters for 3d4 and 3d6 ions using ALTRAN and the tensor method. Four orthorhombic cases are considered. Importance of D (λ3), D (λ4), E (λ3) and E (λ4) is verified. Differences between the previous and present results are discussed. An application to FeF2 is considered

EMR-related problems at the interface between the crystal field Hamiltonians and the zero-field splitting Hamiltonians

The interface between optical spectroscopy, electron magnetic resonance (EMR), and magnetism of transition ions forms the intricate web of interrelated notions. Major notions are the physical Hamiltonians, which include the crystal field (CF) (or equivalently ligand field (LF)) Hamiltonians, and the effective spin Hamiltonians (SH), which include the zero-field splitting (ZFS) Hamiltonians as well as to a certain extent also the notion of magnetic anisotropy (MA). Survey of recent literature has revealed that this interface, denoted CF (LF) ↔ SH (ZFS), has become dangerously entangled over the years. The same notion is referred to by three names that are not synonymous: CF (LF), SH (ZFS), and MA. In view of the strong need for systematization of nomenclature aimed at bringing order to the multitude of different Hamiltonians and the associated quantities, we have embarked on this systematization. In this article, we do an overview of our efforts aimed at providing a deeper understanding of the major intricacies occurring at the CF (LF) ↔ SH (ZFS) interface with the focus on the EMR-related problems for transition ions

Determination of Crystal-Field Energy Levels and Temperature Dependence of Magnetic Susceptibility for Dy³⁺ in [Dy₂Pd] Heterometallic Complex

This study is the first in a series of experimental and theoretical investigations of the crystal-field (CF) energy levels obtained from optical electronic spectra for selected heterometallic 4f-3d compounds intensively studied for the development of novel single-molecule magnets (SMMs). An intriguing question is why the [{Dy^III(hfac)₃}₂Cu^II(dpk)₂] (abbreviated as [Dy₂Cu]; Hhfac = 1,1,1,5,5,5-hexafluoropentane-2,4-dione, Hdpk = di-2-pyridyl ketoxime) has antiferromagnetic coupling, whereas [Gd₂Cu] and heavy [Ln₂Cu] systems usually show ferromagnetic coupling. As the first step to explain this peculiarity, the recently synthesized complex, [Dy₂Pd], is investigated. This complex is isostructural with [Dy₂Cu] yet contains the diamagnetic Pd ion instead of the magnetic Cu­(II) ion. Experimental energy levels of Dy³⁺ ions in the powder [Dy₂Pd] sample were determined from the 4.2 K absorption spectra. CF analysis was performed yielding the fitted free ion and CF parameters. The number of freely varied parameters was restricted using the superposition model. The fittings yield very satisfactory agreement between the experimental and the calculated energy levels (<i>rms</i> = 12.0 cm^–1). The energies and exact composition of the state vector for the ground multiplet ⁶H_15/2 of Dy³⁺ are determined. These results are used for the simulation of the temperature dependence of the magnetic susceptibility, which enables the theoretical interpretation of the experimentally measured magnetic susceptibility in the range 1.8–300 K for the [Dy₂Pd] complex. This study provides background for the subsequent investigation of the magnetic exchange interactions in the pertinent heterometallic complexes