Hybrid Molecular Magnets

The research field of molecular spintronics strives at combining molecular electronics and conventional spintronics, two areas that have already led to prominent and high-revenue applications such as GMR/TMR-based memory devices and organic LEDs, respectively. Integrating the rich versality and functionality of organic molecules with the spin degree of freedom aims to develop improved, but also novel nanoelectronic device concepts with reduced power consumption, lower cost, and smaller size.

Hybrid molecular magnets (HMM) represent a specific approach to molecular spintronics that is based on the complex interaction of organic molecules with inorganic substrates. Organic-inorganic interfaces are necessarily formed when functional molecular units are deposited on supports or electrodes, which are mandatory for the design of spintronic devices. HMM arise when organic, typically aromatic molecules chemisorb to ferromagnetic substrates, such as single-crystalline 3d transition-metal surfaces. The chemisorption is governed by the hybridization between molecular π-orbitals and d-states of the substrate. The spin-split band structure of the latter leads to different hybridization for spin-up and spin-down states. This spin-dependent hybridization induces a spin-imbalanced density of states in the adsorbed molecule, resulting in an induced magnetic moment for strong hybridization and tunneling spin-filter properties for weak hybridization. The spin-dependent hybridization also modifies the magnetic moment, exchange interactions, and magnetic anisotropy of the involved substrate atoms, which can eventually lead to so-called magnetic hardening, i.e., the molecule and the substrate atoms directly bound to it constitute an HMM with enhanced coercivity and blocking temperature. Hence, HMMs are expected to enable the fabrication of devices with higher data storage density and simultaneously improved energy efficiency that still operate at room temperature.

Developing a better understanding of the molecule-substrate interaction and its implications on the local electronic and magnetic properties in both the substrate and the molecule requires well-defined experimental conditions, which we aim to achieve with experiments at low temperatures, in ultrahigh vacuum, and on clean, single-crystalline surfaces. The PGI-6 operates two experimental facilities (Nano-Spintronics-Cluster-Tool and Joule-Thompson STM) that enable investigations of the structural, electronic, and magnetic properties of organic-inorganic molecule-substrate hybrid systems by spin-polarized scanning tunneling microscopy and spectroscopy (STM/STS) on length scales down to the atomic level.

Our experimental work is one of three complementary pillars on which research on molecular spintronics is based: Chemical synthesis of molecules, theoretical modeling of molecule- substrate interfaces, and experimental realization and investigation of organic-inorganic hybrid systems. These are intensively pursued and closely cooperate in Jülich, targeting the development of single-molecule and hybrid spintronics as a major topic.

Results:

1. Cyclophane with eclipsed pyrene units enables construction of spin interfaces with chemical accuracy
2. Ultra-High Vacuum Deposition of Pyrene Molecules on Metal Surfaces
3. Magnetic subunits within a single molecule–surface hybrid
4. Adsorption phenomena of cubane-type tetranuclear Ni(II) complexes with neutral, thioether-functionalized ligands on Au(111)
5. Structural integrity of single bis(phthalocyaninato)-Neodymium(III) molecules on metal surfaces with different reactivity
6. Accessing 4f-states in single-molecule spintronics