Spin anisotropy effects in dimer single molecule magnets

Abstract

We present a model of equal spin $s_1$ dimer single molecule magnets. The spins within each dimer interact via the Heisenberg and the most general set of four quadratic anisotropic spin interactions with respective strengths $J$ and $\{J_j\}$, and with the magnetic induction $\mathbf{B}$. We solve the model exactly for $s_1=1/2,1,5/2$, and for antiferromagnetic Heisenberg couplings ($J<0$), present $\mathbf{M}(\mathbf{B})$ curves at low $T$ for these cases. Low-$T$ $C_V(\mathbf{B})$ curves for $s_1=1/2$ and electron paramagnetic susceptibility $\chi (\mathbf{B},\omega )$ for $s_1=1$ are also provided. For weak anisotropy interactions, we employ a perturbative treatment, and show that the Hartree and extended Hartree approximations lead to reliable analytic results at low $T$ and large $B$ for these quantities and for the inelastic neutron scattering cross-section $S(\mathbf{B},\mathbf{q},\omega )$. Our results are discussed with regard to existing $\mathbf{M}(\mathbf{B})$ experiments on $s_1=5/2$ Fe${}_2$ dimer single molecule magnets, and suggest that one of them contains a substantial amount of single-ion anisotropy, without any sizeable global spin anisotropy. We urge further experiments of the above types on single crystals of Fe${}_2$ and on some $s_{=}9/2$ [Mn${}_4$]${}_2$ dimers, in order to elucidate the precise values of the various microscopic interactions.

30 pages, 25 figures, submitted to Phys. Rev. B

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Cited by in corpus (7)

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• Single-ion and exchange anisotropy effects and multiferroic behavior in high-symmetry tetramer single molecule magnets
• Theory of high-symmetry tetramer single molecule magnets
• The Schottky-type specific heat as an indicator of relative degeneracy between ground and first-excited states: the case study of regular Ising polyhedra
• Field-induced level crossings in spin clusters: Thermodynamics and magneto-elastic instability
• Breakdown of an intermediate plateau in the magnetization process of anisotropic spin-1 Heisenberg dimer: theory vs. experiment
• Effect of Single-ion Anisotropy on Magnetocaloric Properties of Frustrated Spin-$s$ Ising Nanoclusters