Bulled Johnathan M, Paddison Joseph A M, Wildes Andrew, Lhotel Elsa, Cassidy Simon J, Pato-Doldán Breogán, Gómez-Aguirre L Claudia, Saines Paul J, Goodwin Andrew L
Inorganic Chemistry Laboratory, University of Oxford, South Parks Road, Oxford OX1 3QR, United Kingdom.
Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA.
Phys Rev Lett. 2022 Apr 29;128(17):177201. doi: 10.1103/PhysRevLett.128.177201.
In the dense metal-organic framework Na[Mn(HCOO)_{3}], Mn^{2+} ions (S=5/2) occupy the nodes of a "trillium" net. We show that the system is strongly magnetically frustrated: the Néel transition is suppressed well below the characteristic magnetic interaction strength; short-range magnetic order persists far above the Néel temperature; and the magnetic susceptibility exhibits a pseudo-plateau at 1/3-saturation magnetization. A simple model of nearest-neighbor Heisenberg antiferromagnetic and dipolar interactions accounts quantitatively for all observations, including an unusual 2-k magnetic ground state. We show that the relative strength of dipolar interactions is crucial to selecting this particular ground state. Geometric frustration within the classical spin liquid regime gives rise to a large magnetocaloric response at low applied fields that is degraded in powder samples as a consequence of the anisotropy of dipolar interactions.
在致密金属有机框架Na[Mn(HCOO)₃]中，Mn²⁺离子（S = 5/2）占据了“延龄草”网的节点。我们表明该系统存在强烈的磁阻挫：奈尔转变被强烈抑制至远低于特征磁相互作用强度；短程磁有序在远高于奈尔温度时持续存在；并且磁化率在1/3饱和磁化强度处呈现出一个伪平台。一个包含最近邻海森堡反铁磁和偶极相互作用的简单模型定量地解释了所有观测结果，包括一个不寻常的2 - k磁基态。我们表明偶极相互作用的相对强度对于选择这个特定的基态至关重要。经典自旋液体区域内的几何阻挫在低外场下产生了大的磁热响应，由于偶极相互作用的各向异性，粉末样品中的这种响应会减弱。
