Single‐Chain Magnet Based on Cobalt(II) Thiocyanate as XXZ Spin Chain
Single‐Chain Magnet Based on Cobalt(II) Thiocyanate as XXZ Spin Chain
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DOI：
10.1002/chem.201903924
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发表时间：
2019-11
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通讯作者：
M. Rams;Aleksej Jochim;Michael Böhme;T. Lohmiller;Magdalena Ceglarska;M. Rams;A. Schnegg;W. Plass;C. Näther
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作者：
M. Rams;Aleksej Jochim;Michael Böhme;T. Lohmiller;Magdalena Ceglarska;M. Rams;A. Schnegg;W. Plass;C. Näther
摘要[Co（NCS）2（4-甲氧基吡啶）2]n中的钴（II）通过硫氰酸根阴离子对连接成线性链。与以前的结构测定相反，已经发现存在两个晶体学上独立的钴（II）中心。在反铁磁态，在临界温度（Tc = 3.94K）和临界磁场（Hc =290 Oe）以下，观察到铁磁链的缓慢弛豫.它们主要源于磁结构中的缺陷，这已经通过微磁Monte Carlo模拟和使用原始样品和缺陷样品的交流测量来阐明。长自旋链和短自旋链的弛豫能垒分别为Δτ1=44.9（5）K和Δτ2=26.0（7）K。使用频域EPR光谱测量的自旋激发能为19.1 cm−1，并且由于磁有序而偏移0.1 cm−1。从头计算显示两个CoII中心的易轴各向异性，以及交换各向异性Jxx/Jzz为0.21。XXZ各向异性海森堡模型（通过使用密度重整化矩阵群技术求解）用于协调比热，磁化率和EPR数据。
Abstract The cobalt(II) in [Co(NCS)2(4‐methoxypyridine)2]n are linked by pairs of thiocyanate anions into linear chains. In contrast to a previous structure determination, two crystallographically independent cobalt(II) centers have been found to be present. In the antiferromagnetic state, below the critical temperature (T c=3.94 K) and critical field (H c=290 Oe), slow relaxations of the ferromagnetic chains are observed. They originate mainly from defects in the magnetic structure, which has been elucidated by micromagnetic Monte Carlo simulations and ac measurements using pristine and defect samples. The energy barriers of the relaxations are Δτ1=44.9(5) K and Δτ2=26.0(7) K for long and short spin chains, respectively. The spin excitation energy, measured by using frequency‐domain EPR spectroscopy, is 19.1 cm−1 and shifts 0.1 cm−1 due to the magnetic ordering. Ab initio calculations revealed easy‐axis anisotropy for both CoII centers, and also an exchange anisotropy Jxx/Jzz of 0.21. The XXZ anisotropic Heisenberg model (solved by using the density renormalization matrix group technique) was used to reconcile the specific heat, susceptibility, and EPR data.