Quantum rotational band model for the Heisenberg molecular magnet {Mo72Fe30}
Quantum rotational band model for the Heisenberg molecular magnet {Mo72Fe30}
复制标题
海森堡分子磁体 {Mo72Fe30} 的量子旋转带模型
DOI：
10.1209/epl/i2001-00599-0
复制
发表时间：
2001
期刊：
影响因子：
1.8
通讯作者：
Robert Modler
中科院分区：
文献类型：
--
作者：
J. Schnack;M. Luban;Robert Modler
我们推导了分子磁体{Mo_（72）Fe_（30）}的低温性质，其中30个Fe ~（3+）顺磁离子占据了一个二十面体的位置，并通过各向同性的最近邻反铁磁海森堡交换作用相互作用.我们的模型的核心思想（J. S。& M. L.）的范围内。低位激发形成一系列“旋转带”，即，对于每个这样的带，激发能量平方地依赖于总自旋量子数。对于低于50 mK的温度，我们预测，磁化强度是由一个阶梯与75等距步骤的磁场增加到一个临界值和饱和的更高的领域。对于更高的温度，热加宽效应冲洗出阶梯，并在临界场以下产生线性斜坡，这已经被我们的测量所证实（R。M.）。我们表明，最低的两个旋转带分开的能隙为0.7毫电子伏，这可以通过EPR和非弹性中子散射测量进行测试。我们还预测在低于0.1 K的温度下发生共振的质子NMR自旋晶格弛豫率与水平交叉。由于旋转带表征了许多磁性分子的光谱，我们的方法开辟了一条新的道路，描述了它们的低温行为，这是不可访问的。
We derive the low-temperature properties of the molecular magnet {Mo72Fe30}, where 30 Fe3+ paramagnetic ions occupy the sites of an icosidodecahedron and interact via isotropic nearest-neighbour antiferromagnetic Heisenberg exchange. The key idea of our model (J. S. & M. L.) is that the low-lying excitations form a sequence of "rotational bands", i.e., for each such band the excitation energies depend quadratically on the total spin quantum number. For temperatures below 50 mK we predict that the magnetisation is described by a staircase with 75 equidistant steps as the magnetic field is increased up to a critical value and saturated for higher fields. For higher temperatures thermal broadening effects wash out the staircase and yield a linear ramp below the critical field, and this has been confirmed by our measurements (R. M.). We demonstrate that the lowest two rotational bands are separated by an energy gap of 0.7 meV, and this could be tested by EPR and inelastic neutron scattering measurements. We also predict the occurrence of resonances at temperatures below 0.1 K in the proton NMR spin-lattice relaxation rate associated with level crossings. As rotational bands characterize the spectra of many magnetic molecules, our method opens a new road towards a description of their low-temperature behaviour which is not otherwise accessible.