论文标题
实现$α$和协调框架的$β$阶段的Square和diamond晶格$ s = 1/2 $ s = 1/2 $ s = 1/2 $ s = 1/2 $ s = 1/2 $ s = 1/2 $ s = 1/2 $ s = 1/2
Realising square and diamond lattice $S=1/2$ Heisenberg antiferromagnet models in the $α$ and $β$ phases of the coordination framework, KTi(C$_2$O$_4$)$_2\cdot$\textit{x}H$_2$O
论文作者
论文摘要
我们报告了$ s = 1/2 $ ti $^{3+} $协调框架的两个伪造 - 孔形成的晶体结构和磁性特性，单晶X射线和粉末中子衍射测量值（$α$ -KTI（C $ _2 $ _2 $ o $ _4 $）$ _ 2 \ cdot $ xh $ _2 $ o确认其在Tetragonal $ i4/mcm $太空集团中的结构，该结构具有Ti $^{3+} $ ions ti $^$^+} $ ions Square Planem and Square plane。磁力测定法和特定的热量测量结果显示出弱的抗铁磁相互作用，$ j_1 \大约7 $ k和$ j_2/j_1 = 0.11 $，表明最近和下一个最新的邻居相互作用有轻微的挫败感。低于$ 1.8 $ k，$α$经历了向G型反铁磁序的过渡，并沿着四方结构的$ c $轴对齐。 $α$中Ti $^{3+} $的估计有序矩从仅旋转的值抑制至$ 0.62（3）〜μb $，从而验证了系统内磁相互作用的二维性质。 $β$ -KTI（c $ _2 $ o $ _4 $）$ _ 2 \ cdot $ 2H $ _2 $ o，另一方面，在六边形$ p6_2222 $结构中实现了一个三维钻石磁力磁力网络。从磁力测定法和特定的热数据中提取了$ j \ of $ j \大约54 $ k的抗磁交换耦合 - 比$α$中的数量级。 $β$在$ t_n = 28 $ k处进行néel订购，磁矩在$ ab $平面中对齐，并且稍微减少的订购矩$ 0.79〜μb $ $^$^$^{3+} $。通过密度功能理论的计算，我们解决了$α$和$β$ psoudo-polymorphs之间交换参数的巨大差异的起源。鉴于他们观察到的磁性行为，我们建议$α$ -KTI（c $ _2 $ o $ _4 $）$ _ 2 \ cdot $ xh $ _2 $ o和$β$ -kti（c $ _2 $ _2 $ o $ _4 $ _4 $ _4 $ _ $ _ $ _ 2 \ 2 \ cd $ _2 \ cd $ 2H $ _2 $ _2 $ _2 $ a y y y $ a y y y y y y y y y y y y y y y y y y y y y y y y y y y y y y y $ s $ 2抗铁磁铁。
We report the crystal structures and magnetic properties of two psuedo-polymorphs of the $S=1/2$ Ti$^{3+}$ coordination framework, KTi(C$_2$O$_4$)$_2\cdot$xH$_2$O. Single-crystal X-ray and powder neutron diffraction measurements on $α$-KTi(C$_2$O$_4$)$_2\cdot$xH$_2$O confirm its structure in the tetragonal $I4/mcm$ space group with a square planar arrangement of Ti$^{3+}$ ions. Magnetometry and specific heat measurements reveal weak antiferromagnetic interactions, with $J_1\approx7$ K and $J_2/J_1=0.11$ indicating a slight frustration of nearest- and next-nearest-neighbor interactions. Below $1.8$ K, $α$ undergoes a transition to G-type antiferromagnetic order with magnetic moments aligned along the $c$ axis of the tetragonal structure. The estimated ordered moment of Ti$^{3+}$ in $α$ is suppressed from its spin-only value to $0.62(3)~μ_B$, thus verifying the two-dimensional nature of the magnetic interactions within the system. $β$-KTi(C$_2$O$_4$)$_2\cdot$2H$_2$O, on the other hand, realises a three-dimensional diamond-like magnetic network of Ti$^{3+}$ moments within a hexagonal $P6_222$ structure. An antiferromagnetic exchange coupling of $J\approx54$ K -- an order of magnitude larger than in $α$ -- is extracted from magnetometry and specific heat data. $β$ undergoes Néel ordering at $T_N=28$ K, with the magnetic moments aligned within the $ab$ plane and a slightly reduced ordered moment of $0.79~μ_B$ per Ti$^{3+}$. Through density-functional theory calculations, we address the origin of the large difference in the exchange parameters between the $α$ and $β$ psuedo-polymorphs. Given their observed magnetic behaviors, we propose $α$-KTi(C$_2$O$_4$)$_2\cdot$xH$_2$O and $β$-KTi(C$_2$O$_4$)$_2\cdot$2H$_2$O as close to ideal model $S=1/2$ Heisenberg square and diamond lattice antiferromagnets, respectively.
