The mechanism of magnetic interactions in the bulk ferromagnet para(methylthio)phenyl nitronyl nitroxide (YUJNEW):: A first principles, bottom-up, theoretical study
The mechanism of magnetic interactions in the bulk ferromagnet para(methylthio)phenyl nitronyl nitroxide (YUJNEW):: A first principles, bottom-up, theoretical study
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DOI：
10.1002/chem.200400493
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发表时间：
2004-12-17
影响因子：
4.3
通讯作者：
Novoa, JJ
中科院分区：
文献类型：
--
作者：
Deumal, M;Bearpark, MJ;Novoa, JJ
从理论上重新研究了块状铁磁体对（甲基硫）苯基硝基氮氧化物晶体（YUJNEW）的磁相互作用机制，仅使用从头计算的数据，避免了任何先验假设。我们首先计算晶体中所有独特的自由基对之间的微观磁相互作用（JAB交换耦合），然后从相应的海森堡哈密顿能级生成宏观磁性。因此，我们提出了一个第一原则，自下而上（即微观到宏观）的方法，将理论和实验结合在一起。我们利用先前报道的298和114 K晶体结构的数据，以及本工作中完全报道的10 K中子衍射结构的数据，应用这一策略来研究YUJNEW的磁性。298 K下的新磁拓扑是二维的：非相互作用平面，具有三个不同的平面内JAB对相互作用（+0.24,+0.09和-0.11 cm(-1)）和一个数值可忽略的平面间JAB相互作用（+0.02 cm(-1)）。相比之下，114 K和10 K的磁拓扑是三维的，在114 K时具有两个不可忽略的面内JAB常数（+0.11和+ 0.07 cm(-1)）；+0.22和+0.07 cm（-1）在10 K)和一个平面间对相互作用(+0.07 cm（-1）在114 K；+ 0.08厘米（-1）在10 K)。虽然这种三维磁性拓扑结构与YUJNEW是块状铁磁体相一致，但在114 K下，计算磁化率chiT(T)数据与实验磁化率chiT(T)数据只有定性的一致。然而，实验chiT(T)曲线在10 K时定量再现。热容曲线在0.12 K左右出现峰值，接近实验估计峰值（0.20 K）。
The mechanism of magnetic interactions in the bulk ferromagnet para-(methylthio)phenyl nitronyl nitroxide crystal (YUJNEW) has been theoretically reinvestigated, using only data from ab initio calculations and avoiding any a priori assumptions. We first calculate the microscopic magnetic interactions (JAB exchange couplings) between all unique radical pairs in the crystal, and then generate the macroscopic magnetic properties from the energy levels of the corresponding Heisenberg Hamiltonian. We thus propose a first principles, bottom-up (i.e. micro-to-macro) approach that brings theory and experiment together. We have applied this strategy to study the magnetism of YUJNEW using data from the previously reported 298 and 114 K crystal structures, and also data from a 10 K neutron diffraction structure fully reported in this work. ne magnetic topology at 298 K is two-dimensional: noninteracting planes, with three different in-plane JAB pair interactions (+0.24, +0.09, and -0.11 cm(-1)) and one numerically negligible (+0.02 cm(-1)) inter-plane JAB interaction. In contrast, the magnetic topology at 114 and 10 K is three-dimensional, with two non-negligible in-plane JAB constants (+0.11 and + 0.07 cm(-1) at 114 K; +0.22 and +0.07 cm(-1) at 10 K) and one interplane pair interaction (+0.07 cm(-1) at 114 K; + 0.08 cm(-1) at 10 K). Although this three-dimensional magnetic topology is consistent with YUJNEW being a bulk ferromagnet, there is only a qualitative agreement between computed and experimental magnetic susceptibility chiT(T) data at 114 K. However, the experimental chiT(T) curve is quantitatively reproduced at 10 K. The heat capacity curve presents a peak at around 0.12 K, close to the estimated experimental peak (0.20 K).