Characteristics of the Magnetically Ordered High-SpinS=2 Fe²⁺Ion Systems Potentially Suitable for High-Magnetic-Field and High-Frequency EMR Studies

Abstract

This review is the first one in a planned series on the systems potentially suitable for highmagnetic-field and high-frequency electron magnetic resonance (HMF-EMR) studies. Such systems must best exhibit large or very large zero-field splitting (ZFS). The transition metal 3d 4 and 3d 6 ions with an orbital singlet ground state (OSGS) with the spin S=2 in some crystals may provide most suitable examples for applications of the HMF-EMR techniques. The compounds for which an evidence of an OSGS (S=2) exists can be classified into the following groups: (a) magnetically ordered at low temperatures, (b) magnetically ordered at higher temperatures, and (c) not ordered magnetically down to very low temperatures. Our literature search has also identified other groups of the 3d 4 and 3d 6 ions: (d) magnetically ordered compounds but exhibiting substantial orbital degeneracy and (e) biological systems. The largest sub-class of the S=2 systems consists of the high-spin Fe 2+ ion systems. To conform to the main theme of the Workshop, this review focuses on the magnetically ordered high-spin S=2 Fe 2+ ion systems potentially suitable for HMF-EMR studies. The data for the group (a) are presented in the form of a detailed review. For each ion/compound system we provide (i) brief characteristics, (ii) survey of the experimental as well as theoretical methods employed so far, especially those used for determination of the ZFS parameters, and (iii) selected major references as 'pointers' for further studies and literature searches. The groups (b) and (d) are not of prime interest for the present study, however, summary tables with basic pertinent data are included for completeness. The groups (c) and (e) deserve separate reviews. The data collected and analysed in this review may provide guidance for future HMF-EMR studies as well as enable correlation of the experimental ZFS data with the predictions of the microscopic spin Hamiltonian theory developed by us.KEYWORDS: magnetic materials, high-magnetic-field and high-frequency electron magnetic resonance, Fe 2+ ions, orbital singlet ground state, high spin S=2, very large zero-field splitting

Hybrid quantum-classical Monte Carlo study of a molecule-based magnet

“…(1) can explain the persistence of negative magnetization below T comp in small fields: flipping the orbital angular momentum L z i requires an energy of 2|λ|L cf S ≈ 175 K ≫ T comp . By contrast, the single-ion anisotropy D ∼ λ 2 /∆ experienced by the Fe(II) moments in most materials is less than 10 K [9]. So the energy barrier 4D for flipping the Fe(II) spin is smaller than about 40 K, which is comparable to T comp ≈ 32 K. Finally, Eq.…”

Current status of the proposals for unification of notations and guidelines for data presentation in the EMR Area: Blueprint for future actions

“…Usage of truncated forms of ZFS Hamiltonian. This includes [17] cases of (a) some independent ZFS terms set to zero, (b) omission of one of several interdependent ZFS terms, and (c) neglect of some operator terms leading to specific definitions of ZFS parameters used, e.g., magnetization and high-magnetic-field and high-frequency EMR (see, e.g., [44]) studies of Mn~2 (S = 10) complexes.…”

Comparative Analysis of Experimental and Theoretical Zero-Field Splitting and Zeeman Electronic Parameters for Fe2+ Ions in FeX2·4H2O (X = F, Cl, Br, I) and [Fe(H2O)6](NH4)2(SO4)2

“…[4][5][6]) provide nowadays more reliable experimental ZFS and Ze parameter sets for 3d 4 and 3d 6 (S = 2) ions, e.g. Fe 2+ , Mn 3+ , and Cr 2+ , which usually exhibit large and very large ZFS [3,7]. Similar modeling, using the package MSH/VBA [8,9] based on the microscopic spin Hamiltonian (MSH) approach, has recently been undertaken for [Fe(H 2 O) 6 ](NH 4 ) 2 (SO4) 2 (FASH) [10][11][12].…”