Controlling Ferromagnetic Ground States and Solitons in Thin Films and Nanowires Built from Iron Phthalocyanine Chains

Abstract

Iron phthalocyanine (FePc) is a molecular semiconductor whose building blocks are 1D ferromagnetic chains. It is shown that its optical and magnetic properties are controlled by the growth strategy, obtaining extremely high coercivities of over 1 T and modulating the exchange constant between 15 and 29 K through switching from thin films with controlled orientations, to ultralong nanowires. Magnetization measurements are analyzed using concepts and formulas with broad applicability to all 1D ferromagnetic chains. They show that FePc is best described by a xy model with moments preferentially lying in the molecular planes. The chain Hamiltonian is very similar to that for the classic inorganic magnet CsNiF 3 , but with ferromagnetic rather than antiferromagnetic interchain interactions. The dominant degrees of freedom are topological excitations called solitons, namely moving 1D magnetic domain walls, and at low temperatures and fields a "super-Curie-Weiss" law characteristic of nearly 1D xy and Heisenberg ferromagnets, where susceptibility scales as 1/(T 2 -θ 2 ), is observed. The ability to control the molecular orientation and ferromagnetism of FePc systems, and produce them on flexible substrates, together with excellent transistor characteristics reported previously for phthalocyanine analogues, makes them potentially useful for magneto-optical and spintronic devices.

Porphyrin and phthalocyanine: from molecular materials to aggregates

“…(a) 2D graphdiyne based on porphyrin moieties [79] ; (b) 2D covalent frameworks [80] .；(c) 3D convaltent frameworks [81]. [98] 。为了使产物高水溶 性，使用 1，4-二(吡啶-4-基)苯(DPB)单元被甲基化 是一个可行的思路。Yang 等人在最近的研究中，用 四个中间吡啶亚基的甲基化也有望削弱锌卟啉主链 的堆积，以促进双层超分子靶的可控形成，而苯基 吡啶亚基的引入有助于增强的分子间聚集，从而产 生新的 2D 超分子有机框架 [99] [80] 。Xu 等人在 典型的溶剂热条件下缩合得到了具有四方微孔的卟 啉基共价骨架 TAPP -TFPP -COF，热重分析表明该 晶体结构在 450℃以上仍保持高度稳定 [101] 。Wang 等 人构建了基于卟啉基团的三维共价有机框架。实验 结构表明所合成的三维体系具有互传拓扑结构，并 展现出高表面积。此外，卟啉环的金属化可以对孔 径分布有有效的调节作用 [102] [105] 。与传统的粉末-晶体 COF 相比，它们 通过溶解-重构机制调控乙酸浓度(5 mL/6 M)，实现 了纳米片组成超分子结构。超分子自组装是制备高 有序有机功能分子材料的一种重要策略 [57] [106, 107] 。 含有卟啉、酞菁结构单元的超分子体系可以与其他 功能分子如富勒烯、冠醚、二茂铁等通过非共价键 形成更为复杂的多级组装体系。在这一过程中，有 效的控制所制备体系的选择性、方向性和稳定性是 亟待解决的问题。例如，利用卟啉配合物的特性, 研 究金属卟啉与氨基酸、多肽、核酸等生物功能分子 的自组装正在引起人们的日益重视, 籍此可望通过人 工合成出仿生性高的自组装卟啉超分子体系。更为 重要的是：通过不同类型相互作用的协同搭配，可 F o r R e v i e w O n l y 图 5 基于卟啉、酞菁结构的聚集态相貌调控：(a) 纳米线 [104] ; (b) 纳米片 [105] ；(c) 石墨炔/酞菁复合物 [108] ；(d) 卟啉/组氨酸多级自组装结构 [109] Figure 5 Regulation of aggregation state appearance based on porphyrin and phthalocyanine structure:(a) nanowires [104] ; (b) Nanosheets [105] ; (c) graphdiyne/phthalocyanine complex [108] ; (d) Multistage self-assembly structure based on porphyrin and histidine [109]. 以将单一材料体系整合到一个复杂的多级结构中， 从而实现特定的功能。近年来，大量报导了以卟 啉、酞菁结构单元为砌块, 加入小分子(有机、无机 分子)、大环分子(冠醚、富勒烯、环糊精等)及碳基 材料等, 通过分子间的弱相互作用的超分子体系。 近期，Zhang 等通过无共价键的范德瓦尔斯相互作 用，以石墨炔/石墨烯异质结构作为导电骨架来锚 定单分散钴酞菁(图 5c) [108] 。在该体系中，三类材 料展现出不同的功能：石墨烯为导电层，石墨炔为 吸附层，钴酞菁分子作为功能催化层 [110,111] 。 特别 是石墨炔层提供了特定的螯合位点，有效的抑制了 酞菁类分子团聚，大大提高了催化选择性和稳定性 [112][113][114] 。 Liu 等通过卟啉羧基与组氨酸的氢键/静电 相互作用制备了多阶手性微米花。手性纳米级和多 阶手性微米花与手性组氨酸两亲性分子共组装(图 5d) [109] [46] 。通过有效控制钙钛矿薄膜的结 晶和缺陷是影响钙钛矿太阳能电池(PSCs)性能和稳定 性的关键因素，特别是对于大面积 PSCs 器件的制 备。近期，Cao 等人将表面活性剂类单铵锌卟啉(ZnP) 化合物直接嵌入到甲基铵(MA+)碘化铅钙钛矿薄膜 中，形成以叶片状覆盖面积达 16 cm 2 的大面积均匀 钙钛矿薄膜。使用 ZnP 制备的叶片涂层大面积(1.…”

Modeling the Magnetic Properties of 1D Arrays of FePc Molecules

“…Finally, in a recent work, experimental evidence of magnetic solitons has been found. 14 Since FePc has gained attention partly because of its electrical and magnetic properties, it is important to study how magnetic solitons are developed in this system. In order to shed light on these issues, a theoretical study beginning from first-principles calculations and ending in a magnetic model was carried out to help to understand this and related systems further.…”

“…14,17,21 In this "flat-lying" configuration, two adjacent molecular layers are shifted a distance Δ (see Figure 1c) apart from one another along the Fe−N py bond direction indicated by the a, or alternatively the b, axis in Figure 1a. As a result, the Fe atom in a molecule is close to the center of a N py atom in the molecule beneath it 14,17 (see Figure 1b). In this stacking geometry, Fe atoms form parallel unidimensional chains that deviate from the normal to the molecular plane by an angle φ (see.…”

Antiferromagnetic spin-1 large-D phase in organic spin-chain crystals

“…Iron(II) phthalocyanine (FePc) molecules exhibit various magnetic properties depending on their surrounding environment. [22][23][24][25][26][27][28][29][30] In a frozen nonpolar chlorobenzene solution, Mo ¨ssbauer spectroscopy revealed a quintet ground state (S = 2) of isolated FePc molecules. 30 However, for FePc aggregates such as powder, films and nanostructures, a triplet states (S = 1) was proposed as convinced by Mo ¨ssbauer spectroscopy, 31,32 X-ray magnetic circular dichroism (XMCD), [33][34][35][36] X-ray absorption spectroscopy, 37 and magnetic susceptibility measurements.…”

“…30 However, for FePc aggregates such as powder, films and nanostructures, a triplet states (S = 1) was proposed as convinced by Mo ¨ssbauer spectroscopy, 31,32 X-ray magnetic circular dichroism (XMCD), [33][34][35][36] X-ray absorption spectroscopy, 37 and magnetic susceptibility measurements. 29,32,[38][39][40] The magnetic coupling in the FePc single crystal is sensitive to the chemical coordination of Fe ions, which is determined by the packing geometry (y, w) and the ligand field resulting from different exchange paths. The a-phase of FePc, characterized by a y of B261, behaves as ferromagnetic Ising chains with an easy-axis perpendicular to the molecular plane, and the ferromagnetic (FM) coupling arising from the Fe-Fe interactions.…”