Probing the Magnetic Properties of Three Interconvertible Redox States of a Single-Molecule Magnet with Magnetic Circular Dichroism Spectroscopy

Gonidec, Mathieu; Davies, E. Stephen; McMaster, Jonathan; Amabilino, David B.; Veciana, Jaume

doi:10.1021/ja9095895

Cited by 111 publications

(103 citation statements)

References 19 publications

(30 reference statements)

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“…On the contrary, our data on TbPc 2 multilayers on MgO reveal that vertical interactions accelerate magnetization relaxation. [ 20,21 ] In summary, we have demonstrated that MgO thin fi lms realize the combination of effi cient protection from electron scattering and weak molecule-surface hybridization to achieve optimal properties of SMMs on electrode surfaces. In addition, in the present case of TbPc 2 the molecules are self-assembled into well-ordered islands leading to highly uniform molecular ensembles with out-of-plane easy axes.…”

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confidence: 84%

“…The easy-axis-type magnetic anisotropy imposes an energy barrier of ≈65 meV for magnetization reversal, [ 23 ] which is largest within the whole series of lanthanide-Pc 2 SMMs. [ 14,15 ] On nonmagnetic conducting substrates, only vanishing remanence [6][7][8][9][10] and very narrow hysteresis loops [6][7][8][9] were observed, much smaller than in bulk measurements, [ 20 ] illustrating the disruptive effects of the surface. We note that the adsorption of TbPc 2 on (anti)ferromagnetic materials represents a different situation because of the magnetic exchange interaction with the substrate.…”

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confidence: 99%

“…These values vastly exceed the corresponding records reported for any surface-adsorbed SMM [4][5][6][7][8][9][10][11][12][13]26 ] as well as the ones reported for bulk TbPc 2 . [ 20 ] The large remanence indicates that quantum tunneling of magnetization is strongly suppressed for fi elds below 3 T, with only a very subtle modulation of the relaxation rate across the hysteresis loop.The effect of the tunnel barrier becomes evident when comparing with TbPc 2 directly adsorbed onto Ag(100) where the hysteresis opening is barely visible. In fact, the area of the opening has decreased by a factor of 10 (Figure 1 e).…”

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confidence: 99%

“…We use nonmagnetic, insulating MgO, wellknown in inorganic spintronic applications, [ 17,18 ] which allows to control the electron tunneling rate over many orders of magnitude. [ 19 ] Moreover, we employ the TbPc 2 SMM [ 14,15,[20][21][22][23] as a model system. In the neutral molecule, the Tb(III) ion exhibits an electronic spin state of J = 6.…”

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confidence: 99%

“…In this communication we show that the magnetic remanence and hysteresis opening obtained with TbPc 2 on MgO tunnel barriers outperform the ones of any other surface-adsorbed SMM [4][5][6][7][8][9][10][11][12][13]26 ] as well as those of bulk samples of TbPc 2 . [ 20 ] The scanning tunneling microscopy (STM) images in Figure 1 b,c show that TbPc 2 self-assembles by forming perfectly ordered 2D islands on two monolayers (MLs) of MgO on Ag(100). In line with former results, the SMMs are adsorbed fl at on the surface (cf.…”

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Giant Hysteresis of Single‐Molecule Magnets Adsorbed on a Nonmagnetic Insulator

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metal electrode. We use nonmagnetic, insulating MgO, wellknown in inorganic spintronic applications, [ 17,18 ] which allows to control the electron tunneling rate over many orders of magnitude. [ 19 ] Moreover, we employ the TbPc 2 SMM [ 14,15,[20][21][22][23] as a model system. In the neutral molecule, the Tb(III) ion exhibits an electronic spin state of J = 6. It is sandwiched between two phthalocyanine (Pc) macrocycles (cf. schematic view in Figure 1 a) hosting an unpaired electron delocalized over the Pc ligands. The easy-axis-type magnetic anisotropy imposes an energy barrier of ≈65 meV for magnetization reversal, [ 23 ] which is largest within the whole series of lanthanide-Pc 2 SMMs. [ 14,15 ] On nonmagnetic conducting substrates, only vanishing remanence [6][7][8][9][10] and very narrow hysteresis loops [6][7][8][9] were observed, much smaller than in bulk measurements, [ 20 ] illustrating the disruptive effects of the surface. We note that the adsorption of TbPc 2 on (anti)ferromagnetic materials represents a different situation because of the magnetic exchange interaction with the substrate. [ 24,25 ] In those cases, the SMMs were not shown to exhibit slow relaxation of magnetization. Rather, the hysteresis is linked to the one of the magnetic substrates, i.e., it is not an intrinsic property of the SMMs. Overall, the detailed knowledge on TbPc 2 makes it an ideal candidate to test if a tunnel barrier can boost the magnetic properties of surface-adsorbed SMMs. In this communication we show that the magnetic remanence and hysteresis opening obtained with TbPc 2 on MgO tunnel barriers outperform the ones of any other surface-adsorbed SMM [4][5][6][7][8][9][10][11][12][13]26 ] as well as those of bulk samples of TbPc 2 . [ 20 ] The scanning tunneling microscopy (STM) images in Figure 1 b,c show that TbPc 2 self-assembles by forming perfectly ordered 2D islands on two monolayers (MLs) of MgO on Ag(100). In line with former results, the SMMs are adsorbed fl at on the surface (cf. discussion of our STM and X-ray linear dichroism (XLD) data below). [ 6,27 ] This excludes that the extraordinary magnetic properties observed in this study are due to upstanding molecules having their macrocycles perpendicular to the surface, which would lead to a reduced interaction of the Tb(III) ion with the surface. The high-resolution image in Figure 1 c reveals eight lobes per molecule, reminiscent of the staggered conformation of the two phthalocyanine ligands. [ 27 ] Islands with the identical molecular assembly are formed by TbPc 2 adsorbed directly onto Ag(100), as shown in the Supporting Information.The magnetic properties of the Tb(III) ions in the surfaceadsorbed SMMs are determined by X-ray magnetic circular dichroism (XMCD) measurements at the M 4,5 (3 d → 4 f ) edges of Tb. For sub-MLs of TbPc 2 on MgO we fi nd a strong remanence larger than 40% of the saturation magnetization sat M and Single-molecule magnets (SMMs) [ 1 ] are very promising for molecular spintronics [ 2 ] and quantum information processing, [...

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confidence: 84%

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confidence: 99%

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confidence: 99%

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confidence: 99%

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confidence: 99%

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Giant Hysteresis of Single‐Molecule Magnets Adsorbed on a Nonmagnetic Insulator

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Chiral Influences in Functional Molecular Materials

Amabilino¹

2016

Chirality in Supramolecular Assemblies

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Encyclopedia of Inorganic and Bioinorganic Chemistry

Giansiracusa

Gransbury²,

Chilton

et al. 2011

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Single-Molecule Magnets (SMMs) are finite molecular species that display slow relaxation of their magnetisation, equivalent to a magnetic memory effect. Here we give an overview of how SMM behaviour can arise from the spin properties of a giant molecular spin or unpaired electrons on a single metal centre. We outline the criteria for obtaining SMM properties, and how these have developed through theoretical insight to lead to the rapid advancement of SMM performance. We discuss the progression of the field from the original Mn12 polymetallic cluster, to carefully engineered coordination complexes of Ln ions. Classes of compounds discussed include 3d, 3d-4f and 4f polymetallic clusters, 3d and 4f monometallic complexes, and homo-and hetero-metallic exchange-coupled SMMs, including those bridged by radical ligands and/or encapsulated in endohedral fullerenes. The state-ofthe-art in SMMs is discussed, leaving the reader with an up-to-date understanding of theory and synthetic design, with references to comprehensive reviews.For readers new or returning to the area, we highlight the standard experiments used to characterise SMMs -including magnetic hysteresis, zero-field cooled/field cooled magnetic susceptibility, alternating current susceptibility and magnetisation decay measurements. We highlight the common pitfalls often encountered in the literature in measurements, data analysis and structural correlation of properties. We aim to provide a clear background for relaxation mechanisms in SMMs and the quantification of performance using energy barriers, blocking temperatures and relaxation rate. The reader is directed towards a series of proof-ofconcept publications which have spearheaded the implementation of SMMs towards future applications in high density data storage, quantum information processing and spintronics.

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Probing the Magnetic Properties of Three Interconvertible Redox States of a Single-Molecule Magnet with Magnetic Circular Dichroism Spectroscopy

Cited by 111 publications

References 19 publications

Giant Hysteresis of Single‐Molecule Magnets Adsorbed on a Nonmagnetic Insulator

Giant Hysteresis of Single‐Molecule Magnets Adsorbed on a Nonmagnetic Insulator

Chiral Influences in Functional Molecular Materials

Encyclopedia of Inorganic and Bioinorganic Chemistry

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