Monolayers Of Single Molecule Magnets Research Articles

M\xf6ssbauer spectroscopy of a monolayer of single molecule magnets

The use of single molecule magnets (SMMs) as cornerstone elements in spintronics and quantum computing applications demands that magnetic bistability is retained when molecules are interfaced with solid conducting surfaces. Here, we employ synchrotron Mössbauer spectroscopy to investigate a monolayer of a tetrairon(III) (Fe4) SMM chemically grafted on a gold substrate. At low temperature and zero magnetic field, we observe the magnetic pattern of the Fe4 molecule, indicating slow spin fluctuations compared to the Mössbauer timescale. Significant structural deformations of the magnetic core, induced by the interaction with the substrate, as predicted by ab initio molecular dynamics, are also observed. However, the effects of the modifications occurring at the individual iron sites partially compensate each other, so that slow magnetic relaxation is retained on the surface. Interestingly, these deformations escaped detection by conventional synchrotron-based techniques, like X-ray magnetic circular dichroism, thus highlighting the power of synchrotron Mössbauer spectroscopy for the investigation of hybrid interfaces.

Tuning of a Vertical Spin Valve with a Monolayer of Single Molecule Magnets

AbstractThe synthesis and the chemisorption from solution of a terbium bis‐phthalocyaninato complex suitable for the functionalization of lanthanum strontium manganite (LSMO) are reported. Two phosphonate groups are introduced in the double decker structure in order to allow the grafting to the ferromagnetic substrate actively used as injection electrode in organic spin valve devices. The covalent bonding of functionalized terbium bis‐phthalocyaninato system on LSMO surface preserves its molecular properties at the nanoscale. X‐ray photoelectron spectroscopy confirms the integrity of the molecules on the LSMO surface and a small magnetic hysteresis reminiscent of the typical single molecule magnet behavior of this system is detected on surface by X‐ray magnetic circular dichroism experiments. The effect of the hybrid magnetic electrode on spin polarized injection is investigated in vertical organic spin valve devices and compared to the behavior of similar spin valves embedding a single diamagnetic layer of alkyl phosphonate molecules analogously chemisorbed on LSMO. Magnetoresistance experiments have evidenced significant alterations of the magneto‐transport by the terbium bis‐phthalocyaninato complex characterized by two distinct temperature regimes, below and above 50 K, respectively.

Proximal Magnetometry of Monolayers of Magnetic Moments

We present a method to measure the magnetic properties of monolayers and ultra-thin films of magnetic material. The method is based on low energy muon spin rotation and $\beta$-detected nuclear magnetic resonance measurements. A spin probe is used as a "proximal" magnetometer by implanting it in the substrate, just below the magnetic material. We calculate the expected magnetic field distribution sensed by the probe and discuss its temperature and implantation depth dependencies. This method is highly suitable for measuring the magnetic properties of monolayers of single molecule magnets, but can also be extended to ultra-thin magnetic films.

Loss of single-molecule-magnet behavior of a Mn12-based compound assembled in a monolayer

Magnetic circular dichroism magnetization measurements on a monolayer of single molecule magnets have been performed and the results are presented. At the measurement temperature (2 K) the hysteresis cycle shows no opening, contrary to what is seen in the bulk with SQUID magnetometry. This result could surprisingly imply that XMCD is unsuited for such measurements given the fact that it excites the core electrons at the origin of the magnetism. This result could also mean that the blocking temperature is greatly decreased or that these molecules loose their hallmark when deposited as adsorbed films, precluding therefore their much sought-after use in magnetic memories.

The interaction between a monolayer of single-molecule magnets and a metal surface

We calculate within density functional theory (DFT) and the LSDA+U formalism the electronic properties of a nanostructure in which single-molecule magnets Mn12 are adsorbed via thiol groups onto the Au(111) surface. Our DFT calculation shows 1.23 electrons being transferred from the surface to the Mn12 molecule, dominated by the tail on the electronic charge distribution from the gold slab. LSDA+U calculations reveal that the on-site Coulomb repulsion U does not alter the direction of the electronic charge transfer obtained from DFT, because the gold Fermi level still lies above the lowest unoccupied molecular orbital (LUMO). The U term opens up the energy gap between the highest occupied molecular orbital (HOMO) and the LUMO for an isolated standard Mn12 but it minimally affects the gap for a sulfur-terminated Mn12.