一维铁磁链状化合物$M$（NCS）$_2$（硫脲）$_2$ ; $M$ = Ni，Co的磁基态
Magnetic ground-state of the one-dimensional ferromagnetic chain compounds $M$(NCS)$_2$(thiourea)$_2$; $M$ = Ni, Co
摘要：
两个同构的分子基磁体，Ni（NCS）$_{2}$（硫脲）$_{2}$，$S$ = 1，[硫脲= SC（NH $_2$）$_2$ ]和Co（NCS）$_{2}$（硫脲）$_{2}$，$S$ = 3/2的磁性，其特征在于使用几种技术，以合理化它们与结构参数的关系，并确定由自旋取代引起的磁性变化。零场热容和μ子自旋弛豫测量揭示了低温长程有序的两种化合物，除了伊辛类（$D < 0$）单离子各向异性（$D_{\rm{Co}} \sim$ -100 K，$D_{\rm{Ni}} \sim$ -10 K）。晶体和电子结构，结合直流磁场，确认高度准一维行为，铁磁链内交换相互作用$J_{\rm{Co}}\approx+4$ K和$J_{\rm{Ni}}\sim+100$ K和弱反铁磁链间交换，在$J'$ $\sim-0.1$ K的顺序。电子电荷和自旋密度映射揭示了通过空间交换作为一种机制来解释$J$值的巨大差异，尽管从结构的角度来看，这两种材料中的交换途径高度相似。这两种物质都可以与类似化合物$M$ Cl $_2$（硫脲）$_4$，$M$ = Ni（II）（DTN）和Co（II）（DTC）进行比较，其中已知DTN具有两个磁场诱导的量子临界点。DTN和DTC与这里研究的化合物的直接比较表明，取代卤化物Cl $^-$离子，NCS $^-$离子，导致结构和磁性的急剧变化。
英文摘要：
The magnetic properties of the two isostructural molecule-based magnets, Ni(NCS)$_{2}$(thiourea)$_{2}$, $S$ = 1, [thiourea = SC(NH$_2$)$_2$] and Co(NCS)$_{2}$(thiourea)$_{2}$, $S$ = 3/2, are characterised using several techniques in order to rationalise their relationship with structural parameters and ascertain magnetic changes caused by substitution of the spin. Zero-field heat capacity and muon-spin relaxation measurements reveal low-temperature long-range ordering in both compounds, in addition to Ising-like ($D < 0$) single-ion anisotropy ($D_{\rm{Co}} \sim$ -100 K, $D_{\rm{Ni}} \sim$ -10 K). Crystal and electronic structure, combined with DC-field magnetometry, affirm highly quasi-one-dimensional behaviour, with ferromagnetic intrachain exchange interactions $J_{\rm{Co}}\approx+4$ K and $J_{\rm{Ni}}\sim+100$ K and weak antiferromagnetic interchain exchange, on the order of $J'$ $\sim-0.1$ K. Electron charge and spin-density mapping reveals through-space exchange as a mechanism to explain the large discrepancy in $J$-values despite, from a structural perspective, the highly similar exchange pathways in both materials. Both species can be compared to the similar compounds $M$Cl$_2$(thiourea)$_4$, $M$ = Ni(II) (DTN) and Co(II) (DTC), where DTN is know to harbour two magnetic field-induced quantum critical points. Direct comparison of DTN and DTC with the compounds studied here shows that substituting the halide Cl$^-$ ion, for the NCS$^-$ ion, results in a dramatic change in both the structural and magnetic properties.
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