Magnetic fingerprint of individual Fe4 molecular magnets under compression by a scanning tunnelling microscope

Single-molecule magnets (SMMs) present a promising avenue to develop spintronic technologies. Addressing individual molecules with electrical leads in SMM-based spintronic devices remains a ubiquitous challenge: interactions with metallic electrodes can drastically modify the SMM\u2019s properties by charge transfer or through changes in the molecular structure. Here, we probe electrical transport through individual Fe4 SMMs using a scanning tunnelling microscope at 0.5 K. Correlation of topographic and spectroscopic information permits identification of the spin excitation fingerprint of intact Fe4 molecules. Building from this, we find that the exchange coupling strength within the molecule\u2019s magnetic core is significantly enhanced. First-principles calculations support the conclusion that this is the result of confinement of the molecule in the two-contact junction formed by the microscope tip and the sample surface

Electrochemical Gating Single-Molecule Circuits with Parallel Paths

# These authors contributed equally to this work.电化学门控已成为一种可行且高效调节单分子电导的方法。在本研究中,我们证实了具有两个平行苯环的单分子电路中电子传输可以通过电化学门控控制。首先,我们利用STM-BJ技术以金为电极构筑了具有两条平行路径的单分子结。与单条路径的单分子结相比,两条路径的分子结由于具有增强性量子干涉效应,具有2.82倍的电导值。进一步地,我们利用电化学门控对具有两个平行苯环的单分结的电导进行调控,获得了333%·V-1调节比。结合DFT计算,发现在E=EF附近的V形透射系数谱图导致了实验观测的电导门控行为。本研究揭示了具有平行路径的单分子电路的电化学门控行为,并为设计高性能分子器件的分子材料提供了新的途径。通讯作者:周小顺E-mail:[email protected]:Xiao-ShunZhouE-mail:[email protected].浙江师范大学物理化学研究所,先进催化材料教育部重点实验室,浙江 金华 3210042.上海大学物理系,上海 2004441. Key Laboratory of the Ministry of Education for Advanced Catalysis Materials, Institute of Physical Chemistry, Zhejiang Normal University, Jinhua 321004, Zhejiang, China2. Department of Physics, Shanghai University, Shanghai 200444, Chin

Anomalous stepped-hysteresis and T-induced unit-cell-volume reduction in carbon nanotubes continuously filled with faceted Fe3C nanowires

Ferromagnetically-filled carbon nanotubes have been recently considered important candidates for application into data recording quantum disk devices. Achievement of high filling rates of the ferromagnetic materials is particularly desirable for applications. Here we report the novel observation of carbon nanotubes continuously filled along the capillary with unusual μm-long faceted Fe3C nanowires. Anomalous magnetic features possibly due to strain effects of the crystal facets are reported. Magnetization measurements revealed unusual stepped magnetic hysteresis-loops at 300 K and at 2 K together with an anomalous decrease in the coercivity at low temperature. The observed unusual shape of the hysteresis is ascribed to the existence of an antiferromagnetic transition within or at the boundary of the ferromagnetic facets. The collapse in the coercivity value as the temperature decreases and the characteristic width-enhancement of the hysteresis with the field increasing appear to indicate the existence of layered antiferromagnetic phases, possibly in the strain-rich regions of the nanowire facets. Zero field cooled (ZFC) and field cooled (FC) magnetic curves evidenced presence of magnetic irreversibilities, an indicator of a possible spin-glass-like behavior induced by competing antiferromagnetic and ferromagnetic interactions. Characterization performed with low temperature XRD measurements, further revealed a slight variation in the average Fe3C unit cell parameters, suggesting the absence of additional unit-cell volume induced ferromagnetic transitions at low temperature

Room-temperature tunnel magnetoresistance across biomolecular tunnel junctions based on ferritin

Altres ajuts: ICN2 is funded by the CERCA programme/generalitat de CatalunyaWe report exceptionally large tunnel magnetoresistance (TMR) for biomolecular tunnel junctions based on ferritins immobilized between Ni and EGaIn electrodes. Ferritin stores iron in the form of ferrihydrite nanoparticles (NPs) and fulfills the following roles: (a) it dictates the tunnel barrier, (b) it magnetically decouples the NPs from the ferromagnetic (FM) electrode, (c) it stabilizes the NPs, and (d) it acts as a spin filter reducing the complexity of the tunnel junctions since only one FM electrode is required. The mechanism of charge transport is long-range tunneling which results in TMR of 60 ± 10% at 200 K and 25 ± 5% at room temperature. We propose a magnon-assisted transmission to explain the substantially larger TMR switching fields (up to 1 Tesla) than the characteristic coercive fields (a few Gauss) of ferritin ferrihydrite particles at T < 20 K. These results highlight the genuine potential of biomolecular tunnel junctions in designing functional nanoscale spintronic devices

Chemical tunnel-splitting-engineering in a dysprosium-based molecular nanomagnet

Total control over the electronic spin relaxation in molecular nanomagnets is the ultimate goal in the design of new molecules with evermore realizable applications in spin-based devices. For single-ion lanthanide systems, with strong spin-orbit coupling, the potential applications are linked to the energetic structure of the crystal field levels and quantum tunneling within the ground state. Structural engineering of the timescale of these tunneling events via appropriate design of crystal fields represents a fundamental challenge for the synthetic chemist, since tunnel splittings are expected to be suppressed by crystal field environments with sufficiently high-order symmetry. Here, we report the long missing study of the effect of a non-linear (C4) to pseudo-linear (D4d) change in crystal field symmetry in an otherwise chemically unaltered dysprosium complex. From a purely experimental study of crystal field levels and electronic spin dynamics at milliKelvin temperatures, we demonstrate the ensuing threefold reduction of the tunnel splitting.M.A.S., U.B.H., K.L., and J.Be. acknowledge financial support from the Danish Research Councils for Independent Research (12-125226). M.A.S., U.B.H., M.R, and K.L. acknowledge DANSCATT for financial support for the neutron scattering experiments. For the experiments conducted at FRM II, this project has received funding from the European Union’s 7th Framework Programme for research, technological development and demonstration under the NMI3-II Grant number 283883. M.A.S. thanks the Oticon Foundation (16-2669), and the Augustinus Foundation (16-2917) for financial support in relation to a research stay at Institut für Physikalische Chemie, Universität Stuttgart, Germany. M.P. and J.v.S. thank the DFG for funding (SL104/5-1). K.S.P. thanks the Danish Research Council for Independent Research for a DFF-Sapere Aude Research Talent grant (4090-00201). E.B., A.A, and, J.Ba. acknowledge the financial support of Spanish MINECO project MAT2017-83468-R. M.J. acknowledges the Swiss National Science Foundation.Peer reviewe

Síntese e caracterização espectroscópica e magnetestrutural de complexos polinucleares de metais do bloco d com ligantes B-dicetonatos

Orientadora : Profª Drª Jaísa Fernandes SoaresCo-orientadores : Profª. Drª. Giovana Gioppo Nunes, Prof. Dr. Eduardo Lemos de SáTese (Doutorado) - Universidade Federal do Paraná, Setor de Ciências Exatas, Programa de Pós-Graduação em Química. Defesa: Curitiba, 27/02/2015Inclui referências : f. 166-176Área de concentração: Quimica inorgânicaResumo: Complexos com topologia star-shaped [Fe4(LR)2(dpm)6] (Stotal = 5) despertam atenção pois mantêm suas propriedades como single-molecule magnets (SMMs) quando funcionalizados e depositados em superfícies de ouro metálico. Isso viabiliza possíveis aplicações tecnológicas, além de auxiliar no entendimento dos mecanismos de troca e de relaxação magnéticas apresentados por estes materiais. O intuito de nosso trabalho foi sintetizar novos complexos tetranucleares star-shaped, [M"3M'(LR)2(dpm)6], onde Hdpm = dipivaloilmetano e H3LR = álcool tripédico tipo R-C(CH2OH)3, a partir de rotas sintéticas modulares com o maior controle sintético possível, a fim de produzir compostos heterometálicos puros. Foram utilizados íons metálicos com S elevado nas posições externas da estrutura tetranuclear (M") e um íon central com S baixo (M'), a fim de aumentar o Stotal e a resposta magnética apresentada por este tipo de molécula. A rota sintética em três etapas desenvolvida neste trabalho, na qual há a formação inicial do core {M'(LR)3}3 e posterior reação com três equivalentes de {M"(dpm)2}+, produziu os agregados tetranucleares [Fe3Cr(LEt)2(dpm)6] (Fe3CrLEt), [Fe3V(LEt)2(dpm)6] (Fe3VLEt), [Fe3V(LPh)2(dpm)6] (Fe3VLPh), [Fe4(LEt)2(dpm)6] (A), [Ga3V(LEt)2(dpm)6] (Ga3VLEt) e [Ga3V(LPh)2(dpm)6] (Ga3VLPh), onde H3LEt = 1,1,1-tris(hidroximetil)propano e H3LPh = 1,1,1- tris(hidroximetil)fenilmetano. Estes produtos foram caracterizados por análise elementar, difratometria de raios X, técnicas espectroscópicas (IV-TF, RMN e RPE) e magnéticas (susceptometria DC e AC). A caracterização no estado sólido e em solução de Fe3CrLEt comprovou a formação da espécie tetra(hetero)nuclear com um Stotal = 6 no estado fundamental, porém com um parâmetro D de -0,174(1) cm-1, o qual é menor do que o da espécie homometálica Fe4LEt (D = -0,435(2) cm-1), levando a uma barreira energética de reorientação dos spins baixa (?E = 23 cm-1). A caracterização de Fe3VLEt sem recristalização evidenciou a formação da espécie [Fe3V(LEt)2(dpm)6] e comprovou a eficiência da rota sintética proposta, porém estudos de estabilidade em solução evidenciaram a degradação deste complexo nas espécies Fe4LEt e [Fe(dpm)3]. A estabilidade limitada deste composto, devido à labilidade do íon VIII, leva à cocristalização de espécies Fe3VLEt e Fe4LEt em tentativas de purificação por recristalização. Apesar disso, a espécie Fe3VLEt apresenta tanto um aumento no valor de S da molécula (Stot = 13/2) quanto no valor de D (-0,318(4) cm-1) quando comparada com Fe3CrLEt, o que leva a uma barreira energética de inversão da magnetização (?E = 44 cm-1) similar à da espécie Fe4LEt (?E = 43 cm-1). Além disso, o efeito de relaxação da magnetização por tunelamento quântico é fortemente reduzido na espécie Fe3VLEt em campo zero. Estas características mostram-se promissoras para um SMM. A tentativa de síntese de um agregado com M' = TiIII, que teria S = 7, levou à formação de cristais puros de [Fe4(LEt)2(dpm)6] (A), evidenciando a labilidade elevada do íon TiIII no complexo de interesse em solução. Na síntese dos compostos Fe3VLPh, Ga3VLEt e Ga3VLPh, a metodologia teve que ser levemente adaptada em cada sistema estudado, porém levou à formação dos agregados de interesse, [M"3M'(LR)2(dpm)6], com proporção entre os metais próxima da desejada, 3M" : 1M'. Estes novos compostos auxiliarão nos estudos sobre a influência do vanádio(III) nas propriedades magnéticas dos SMMs M"3VLR. Palavras-chave: magnetismo molecular, single-molecule magnets e síntese modularAbstract: Star-shaped [Fe4(LR)2(dpm)6] complexes (Stotal = 5) have driven scientists' attention because they retain their SMM properties when functionalized and deposited on gold surfaces, enabling possible technological applications as well as the understanding of their magnetic exchange and relaxation mechanisms. The aim of our work was to synthesize new tetranuclear star-shaped complexes, [M"3M'(LR)2(dpm)6], in which Hdpm = dipivaloylmethane and H3LR = tripodal ligands (R-C(CH2OH)3), employing modular synthetic routes with the highest possible synthetic control in order to obtain pure heterometallic compounds. Metal ions with a high S have been used in the external positions of the star-shaped structure (M"), while a central ion with low S (M') has been of interest in order to increase the magnetic response presented by the products. The three-step synthetic route developed in this work, in which there is the initial formation of the core {M'(LR)3}3 followed by subsequent reaction with three equivalents of {M"(dpm)2}+, produced the tetranuclear clusters [Fe3Cr(LEt)2(dpm)6] (Fe3CrLEt), [Fe3V(LEt)2(dpm)6] (Fe3VLEt), [Fe3V(LPh)2(dpm)6] (Fe3VLPh), [Fe4(LEt)2(dpm)6] (A), [Ga3V(LEt)2(dpm)6] (Ga3VLEt) and [Ga3V(LPh)2(dpm)6] (Ga3VLPh), with H3LEt = 1,1,1-tris(hydroxymethyl)propane and H3LPh = 1,1,1- tris(hydroxymethyl)phenylmetane. These products were characterized by elemental analysis, single-crystal X-ray diffractometry, FTIR, NMR and EPR spectroscopies and magnetic measurements (DC and AC susceptometry). The characterization of Fe3CrLEt in the solid state and in solution confirmed the formation of the tetraheteronuclear species with a total S = 6 in the ground state, but with D = - 0,174(1) cm-1, which is smaller than the value given by the homometallic species Fe4LEt (D = -0,435(2) cm-1). This leads to a low energy barrier (?E = 23 cm-1) for magnetization reversal. The characterization of the Fe3VLEt product obtained without recrystallization revealed the formation of the expected species, [Fe3V(LEt)2(dpm)6], proving the efficiency of the proposed synthetic route. However, stability studies in solution showed the degradation of this complex to give both Fe4LEt and [Fe(dpm)3]. The limited stability of this compound is due to the lability of the ion VIII towards ligand substitution and leads to the cocrystallization of Fe3VLEt and Fe4LEt in recrystallization attempts. Despite this, Fe3VLEt presents both an increase in the total S value (S = 13/2) and in the D value (-0,318(4) cm-1) when compared to Fe3CrLEt. These features lead to an energy barrier (?E = 44 cm-1) similar to that found in Fe4LEt (?E = 43 cm-1). Moreover, quantum tunnelling effects are substantially reduced in zero field for Fe3VLEt, a feature that makes this compound a promising SMM. The attempt to synthesize a similar heterometallic complex with M' = TiIII led to the formation of pure crystals of [Fe4(LEt)2(dpm)6] (A), demonstrating the high lability of the TiIII ion in solution. In the synthesis of Fe3VLPh, Ga3VLEt and Ga3VLPh, the threestep route developed in this work had to be slightly adapted to each system, but led to the formation of the desired aggregates, [M"3M'(LR)2(dpm)6], with metal ratios close to the desired 3M" : 1M'. These new complexes will be useful in the elucidation of the influence of vanadium(III) on the magnetic properties of M"3VLR SMMs. Keywords: molecular magnetism, single-molecule magnets and modular synthesis

Single-Molecule Magnets with Trigonal Symmetry of the Coordination Polyhedron: Structure, Magnetic Properties and Deposition on Surfaces

Tato práce se zaměřuje na syntézu, strukturu a magnetické vlastnosti Jedno Iontových Magnetů s trigonální symetrií a jejich depozici na povrchy. První část se zabývá úvodem do tématiky Jedno Molekulových magnetů. Následuje část věnovaná metodám použitým k provedení charakterizací studovaných vzorků, následně je kapitola doplněná o teoretickou část. Dále jsou diskutovány připravené vzorky a následuje diskuze o získaných datech a o dosažení cílů této práce. Závěrečná část obsahuje použitou literaturu a seznam autorových činností v průběhu studia.This thesis focusses on synthesis, structure and magnetization study of Single Ion Magnets with trigonal symmetry and their deposition on surfaces. The first part outlines the introduction into State of the art of the Single Molecule magnets. Followed by description of methods used to perform all discussed characterizations and theoretical background of these methods. In the next part are discussed all the obtained results and it is concluded by discussion about the achieved aims of this thesis. The last part of this thesis provides references and author’s published results.