Ab-initio XRPD crystal structure and giant hysteretic effect (Hc=5.9 T) of a new hybrid terephthalate-based cobalt(II) magnet
Ab-initio XRPD crystal structure and giant hysteretic effect (Hc=5.9 T) of a new hybrid terephthalate-based cobalt(II) magnet
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DOI：
10.1021/cm000386c
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发表时间：
2000-09-01
影响因子：
8.6
通讯作者：
Panissod, P
中科院分区：
文献类型：
--
作者：
Huang, ZL;Drillon, M;Panissod, P
采用水热法合成了一种新型对苯二甲酸钴氢氧化物Co-2(OH)(2)(C8H4O4)。它的晶体结构已由从头算XRPD方法确定(单斜晶系，C2/m，a=19.943(1)，b=3.2895(1)，c=6.2896(3)埃，β=95.746(3)度)，并用Rietveld技术对9301个观测数据(178个独立反射)进行了完全修正，R-p=0.15.对苯二甲酸酯被配位并直接柱撑到氢氧化钴层上，从而形成了三维骨架。由于与对苯二甲酸酯的键合，在氢氧化层内发现了两个结晶学上不同的钴中心，具有不同的八面体取向。磁性研究表明，Co(II)离子之间的层内交换作用是铁磁性的，但整个体系在48K时是反铁磁性的，在0.2T的阈值磁场以上有一个亚磁跃迁。对苯二甲酸酯中共轭pi电子的存在解释了层之间的反铁磁性相互作用。在45K以下，化合物表现出滞后的变磁环和小到约30K的残余磁矩，然后突然上升到15K以下的平台。然而，在低温下，残余磁矩仍然只是完整Co(II)磁矩的一小部分，这是与层间磁矩的非共线取向有关的倾斜反铁磁性的迹象。在4.2K时，磁化曲线显示出5.9T的巨矫顽场，这一定与Co位上极大的单离子各向异性有关。
A new terephthalate-based cobalt hydroxide, Co-2(OH)(2)(C8H4O4), was synthesized by the hydrothermal method. Its crystal structure has been determined by ab-initio XRPD methods (monoclinic, C2/m, a = 19.943(1), b = 3.2895(1), c = 6.2896(3) Angstrom, beta = 95.746(3)degrees) and fully refined by the Rietveld technique down to R-p = 0.15 for 9301 observed data (178 independent reflections). The terephthalates are coordinated and pillared directly to the cobalt hydroxide layers and thus a three-dimensional framework is formed. Because of the bonds with the terephthalates, two crystallographically inequivalent cobalt sites are found inside the hydroxide layers, with different octahedral orientations. Magnetic studies show that the intralayer exchange interaction between Co(II) ions is ferromagnetic but the whole system orders antiferromagnetically at 48 K with a metamagnetic transition above a threshold field of 0.2 T. The existence of conjugated pi electrons in terephthalates explains the antiferromagnetic interactions between the layers. Below 45 K, the compound exhibits a hysteretic metamagnetic loop and a remnant moment that is small down to about 30 K, and then rises suddenly reaching a plateau below 15 K. However, at low temperatures the remnant moment is still only a fraction of the full Co(II) moment, which is a sign of canted antiferromagnetism associated with a non-collinear orientation of the moments between the layers. The magnetization loop shows a giant coercive field of 5.9 T at 4.2 K, which must be related to an extremely large single-ion anisotropy on the Co sites.