Room-temperature magnetic bistability in organic radical crystals: Paramagnetic-diamagnetic phase transition in 1,3,5-trithia-2,4,6-triazapentalenyl
Room-temperature magnetic bistability in organic radical crystals: Paramagnetic-diamagnetic phase transition in 1,3,5-trithia-2,4,6-triazapentalenyl
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DOI：
10.1103/physrevb.65.064434
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发表时间：
2002-02-01
影响因子：
3.7
通讯作者：
Okamoto, H
中科院分区：
文献类型：
--
作者：
Fujita, W;Awaga, K;Okamoto, H
有机自由基1，3，5-三硫杂-2，4，6-三氮杂并环戊二烯基（TTTA）在230-305 K温度范围内表现出顺磁性高温（HT）相和反磁性低温（LT）相之间的一级相变，并具有令人惊讶的宽热滞回线。HT相的晶体结构由一维（1D）规则的π堆积柱和短S。N和S S列间接触。柱内和柱间交换耦合常数分别为J/k（B）= -320 K和zJ '/k（B）=-360 K，表明存在三维磁相互作用。LT相具有抗磁性，这是由堆叠柱中的强交替引起的。差示扫描量热法测量揭示了一个放热和吸热的转变时，冷却和加热，分别与静态磁测量的滞后。观测到的跃迁熵大于自旋贡献的最大估计。R ln 2，表明在此相变中的晶格系统的结合。电子顺磁共振测量也证实了顺磁-反磁相变的磁滞现象。反射光谱表明在相变时的维数的变化，这是与分子间的π积分计算的结果一致。
An organic radical, 1,3,5-trithia-2,4,6-triazapentalenyl (TTTA), exhibits a first-order phase transition between a paramagnetic high-temperature (HT) phase and a diamagnetic low-temperature (LT) phase, with a surprisingly wide thermal hysteresis loop over the temperature range 230-305 K. The crystal structure of the HT phase consists of a one-dimensional (1D) regular pi-stacking column with short S...N and S...S intercolumn contacts. The intra- and intercolumn exchange coupling constants are estimated to be J/k(B) = -320 K and zJ'/k(B) = - 360 K, indicating a 3D magnetic interaction. The LT phase has a diamagnetic property, caused by a strong alternation in the stacking column. The differential scanning calorimetry measurements reveal an exothermic and an endothermic transition upon cooling and heating, respectively, with the hysteresis in agreement with static magnetic measurements. The observed transition entropy is, larger than the Maximum estimation of the spin contribution. R ln 2, suggesting incorporation of the lattice system in this phase transition. The electron paramagnetic resonance measurements also demonstrate the paramagnetic-diamagnetic phase transition with the hysteresis. The reflection spectra suggest a change in dimensionality at the phase transition, which is consistent with the results of the intermolecular overlap-integral calculations.