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首页> 外文期刊>Physical review >Single-ion and exchange anisotropy effects and multiferroic behavior in high-symmetry tetramer single-molecule magnets
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Single-ion and exchange anisotropy effects and multiferroic behavior in high-symmetry tetramer single-molecule magnets

机译：高对称四聚体单分子磁体中的单离子交换各向异性效应和多铁性行为

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We study single-ion and exchange anisotropy effects in equal-spin s_1 tetramer single-molecule magnets exhibiting T_d, D_(4h), D_(2d), C_(4h), C_(4v), or S_4 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 s_1. For AFM tetramers, we illustrate the first-order level-crossing inductions for s_i = 1/2, 1, and 3/2, and obtain preliminary estimates of the microscopic parameters in a Ni_4 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 S_4 and D_(2d) should exhibit both DM interactions and multiferroic states, and we illustrate our predictions for s_1 = 1/2 and 1.
机译：我们研究了具有T_d，D_（4h），D_（2d），C_（4h），C_（4v）或S_4离子位点群对称性的等旋s_1四聚体单分子磁体中的单离子和交换各向异性效应。我们首先在适当的局部坐标下写出群不变的二次单离子和对称各向异性交换哈密顿量。然后，我们以分子或实验室表示形式重写这些局部哈密顿量，以及组不变的Dzyaloshinskii-Moriya（DM）和各向同性的海森堡，双二次和三中心四次哈密顿量。使用单离子自旋矩阵元素的精确紧凑形式，我们在微观各向异性相互作用中将本征态能量解析为一阶，对应于强交换极限，并提供了最低能量各向异性能的简单公式表具有任意s_1的四个铁磁（FM）和反铁磁（AFM）四聚体的本征态流形。对于AFM四聚体，我们说明了s_i = 1 / 2、1和3/2的一阶能级交叉感应，并从磁化数据拟合得到了Ni_4中微观参数的初步估计，表明存在强对称各向异性交换相互作用。给出了热力学，电子顺磁共振吸收和非弹性中子散射截面的准确解析表达式，从而可以确定来自FM四聚体第二激发态流形的三种微观各向异性相互作用。我们还预测对称性为S_4和D_（2d）的四聚体应同时显示DM相互作用和多铁性态，并说明s_1 = 1/2和1的预测。

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