Title

Single-Ion And Exchange Anisotropy Effects And Multiferroic Behavior In High-Symmetry Tetramer Single-Molecule Magnets

Abstract

We study single-ion and exchange anisotropy effects in equal-spin s1 tetramer single-molecule magnets exhibiting Td, D4h, D2d, C4h, C4v, or S4 ionic site point group symmetry. We first write the group-invariant quadratic single-ion and symmetric anisotropic exchange Hamiltonians in the appropriate local coordinates. We then rewrite these local Hamiltonians in the molecular or laboratory representation, along with the group-invariant Dzyaloshinskii-Moriya (DM) and isotropic Heisenberg, biquadratic, and three-center quartic Hamiltonians. Using our exact, compact forms for the single-ion spin matrix elements, we analytically evaluate the eigenstate energies to first order in the microscopic anisotropy interactions, corresponding to the strong exchange limit, and provide tables of simple formulas for the anisotropy energies of the lowest four eigenstate manifolds of ferromagnetic (FM) and antiferromagnetic (AFM) tetramers with arbitrary s1. For AFM tetramers, we illustrate the first-order level-crossing inductions for s1 =1 2, 1, and 3 2, and obtain preliminary estimates of the microscopic parameters in a Ni4 from fits to magnetization data, indicating the presence of strong symmetric anisotropic exchange interactions. Accurate analytic expressions for the thermodynamics, electron paramagnetic resonance absorption, and inelastic neutron scattering cross section are given, allowing for a determination of three of the microscopic anisotropy interactions from the second excited state manifold of FM tetramers. We also predict that tetramers with symmetries S4 and D2d should exhibit both DM interactions and multiferroic states, and we illustrate our predictions for s1 =1 2 and 1. © 2008 The American Physical Society.

Publication Date

5-12-2008

Publication Title

Physical Review B - Condensed Matter and Materials Physics

Volume

77

Issue

18

Number of Pages

-

Document Type

Article

Personal Identifier

scopus

DOI Link

https://doi.org/10.1103/PhysRevB.77.184410

Socpus ID

43549093501 (Scopus)

Source API URL

https://api.elsevier.com/content/abstract/scopus_id/43549093501

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