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Optical Anisotropy in Chiral NanoMagnets: Towards Optical Reading of Spin Orientation – AnisoChirMag

Optical Anisotropy in Chiral Nanomagnets: Towards Optical Reading of Spin Orientattion

AnisoChirMag is an interdisciplinary project which goal is to rationally synthesize chiral molecule-based nano-magnets combining significant magnetic anisotropy and Magneto-Chiral Dichroism (MChD) effect. This effect is proposed as a probe for the optical reading of the spatial orientation of the magnetic moment, i.e. to discriminate among the two possible spin orientations in such bistable materials. The target of the project is to provide a proof-of-concept using 1-D molecular nano-magnet.

Detection of a strong MchD signal in chiral single-chain magnets

La synthèse de nano-aimants chiraux 1-D (appelés chaine-aimants ou Single-Chain Magnets et notés SCMs) construits à partir de complexes 4d ou 5d énantio-purs est spécifiquement ciblée pour démontrer ce concept. <br />Des complexes métalliques d’ions 4d/5d sont des alternatives aux éléments du bloc f pour la préparation d’aimants moléculaires avec des barrières d’énergie élevées de part leur état fondamental anisotrope (couplage spin-orbite important) et leur moment magnétique fort. De plus, ils peuvent établir des interactions d’échange fortes avec d’autres porteurs de spin ce qui est crucial pour des chaine-aimants hétérométalliques performantes. Le nombre d’exemples de complexes de coordination d’ions 4d/5d permettant la construction de nano-aimants moléculaires est très limité et les composés hétérométalliques comportant exclusivement des centres métalliques 4d and 5d restent extrêmement rares en dépit de leur propriétés magnétiques prometteuses (hautes températures de blocage et moments effectifs élevés) qui sont attendues.

AnisoChirMag is a project implemented in three well-defined and complementary tasks corresponding respectively to (i) the preparation of chiral 4d/5d complexes, (ii) their utilization as precursors for the construction of enantiopure 1-D nano-magnets, and (iii) the studies of their magneto-chiral properties.
Task 1 is devoted to the synthesis of a family of enantiopure ligands and subsequently the chiral 4d/5d complexes. The targeted complexes have been designed to become building units, either as metallo-ligand or complex with substitutable coordination sites, for the formation coordination polymers. All complexes will be thoroughly characterized; their crystal structures, optical properties (natural circular dichroism), and magnetic properties will be investigated. Special attention will be devoted to the assessment of the magnetic anisotropy of the novel 4d and 5d complexes.
The chiral heterometallic 1-D nano-magnets will be synthesized under Task 2 using a building-block approach. Their design rest on two main target-characteristics that are state-of-the-art magnetic behaviors (high blocking temperature, low relaxation rates, etc.) and specific optical features (strong natural optical activity, large extension constant associated to the magnetic centers). Accurate investigation and analysis of the magnetic properties will be undertaken in order identify the most promising SCM for MChD characterizations.
In Task 3, the magneto-optical anisotropy properties will be investigated and the optical detection of the spin orientation will be tackled for best adapted SCM.

An heptacoordinated Fe(II) chiral complex was synthesized and characterized by infrared spectroscopy as well as single-crystal X ray diffraction. Its optical properties will be soon studied by circular dichroisme on both enantiomers.

First associations were performed between the Fe(II) complex and a Cr(III) metalloligand. Crystals were obtained and their crystal data collection is pending. Infrared spectroscopy is in agreement with the formation of the targeted CrFe chaine CrFe. A single-Chain Magnet behavior is expected in this system.

Magnetic properties and MChD effect will be studied in priority on both enantiomers.

Our main efforts will be devoted to the preparation of heptacoordinated Mo(III) building units. They will be connected to our chiral units to prepare new chiral SCMs with better physical performances.

Publications in preparation.

AnisoChirMag aims to synthesize chiral molecule-based nano-magnets combining significant magnetic anisotropy and Magneto-Chiral Dichroism (MChD) effect. This effect is proposed as a probe for the optical reading of the spatial orientation of the magnetic moment, i.e. to discriminate among the two possible spin orientations in the bistable state. The goal of the project is to provide a proof-of-concept using 1-D molecular nano-magnets. An important part of the project deals with the elaboration of new chiral 1-D nano-magnets (called Single-Chain Magnets) which satisfy the magnetic and optical requirements for strong MChD effect.

The project will be implemented in three well-defined and complementary tasks:
i) chiral 4d/5d complexes with large anisotropy will be synthesized and characterized; we target coordination compounds that could be used as metallo-ligands or acceptor (coordinatively unsaturated) metal complexes,
ii) enantiopure heterometallic SCMs will be assembled from these 4d/5d building blocks and
iii) the magnetic and optic properties of the molecule-based nano-magnets will be undertaken.

The molecular chiral components were selected for their intense circular dichroic signals combined to high extinction coefficients. 4d/5d complexes are specifically selected for their strong spin-orbit coupling leading to strong magnetic anisotropy, and for the enhanced exchange interaction taking place with another spin carrier. The incorporation of such 4d and 5d units within chains will lead to SCMs with improved magnetic features (high blocking temperatures and high effective moments) as a result of the combined contributions of large anisotropy and strong exchange. The large magnetic moment of the SCM and the chirality brought by the chemical system are anticipated to give rise to a magneto-chiral response much larger than for a discrete spin system and sufficient to discriminate the two orientation of the magnetization of the SCM. The demonstration of this concept will be the final target of this project. This project will be conducted at Laboratoire de Chimie de Coordination (LCC, UPR 8241) in Toulouse and gather synthetic chemists known for their expertise in the field of molecular magnetism and physicists expert in magnetism and magneto-optical properties.

Project coordinator

Madame Céline Pichon (Laboratoire de Chimie de Coordination)

The author of this summary is the project coordinator, who is responsible for the content of this summary. The ANR declines any responsibility as for its contents.

Partner

LCC Laboratoire de Chimie de Coordination

Help of the ANR 201,490 euros
Beginning and duration of the scientific project: December 2017 - 42 Months

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