liquid-nitrogen temperature [3] or single atoms exhibiting extremely long magnetic relaxation times. [4][5][6] In particular, systems based on late lanthanide family elements, like Dy and Tb, have been largely in focus, including single-molecule, [2,3] singleatom, [4,5] or single-chain magnets. [7,8] Adsorption of SMMs on surfaces allows to study individual molecular units, as well as to realize transport schemes essential for the implementation of SMMs in molecular-scale spintronics or quantum computing devices. [9][10][11][12][13][14][15][16][17] However the transition from bulk to surface-supported systems often goes along with a substantial change or even loss of SMM properties, that is, magnetic moment, magnetic anisotropy, or magnetization behavior. [18][19][20][21] On metallic surfaces, the interaction of the magnetic moments with the surface is rather strong, which is evidenced by the observation of the Kondo effect. [22,23] Thus, benchmark measurements during the last years demonstrating magnetic bistability of surface-adsorbed SMMs have been reported on substrates, where molecules are electronically weakly coupled to -TbPc 2 on HOPG, [24] on MgO/Ag(100) [25] and on graphene/SiC, [26] pushing the blocking temperature (T B ) limit up to 9 K. On the other hand, DySc 2 N@C 80 monolayers on Au(111) [27] recently showed a hysteresis opening at temperatures up to 10 K. In this sense, lanthanide ions encaged in C 80 molecules reportedly outperform most SMMs by their combination of chemical robustness with slow magnetic relaxation. [27][28][29][30][31] To further push the magnetic lifetime in the monolayer regime two important criteria have to be fulfilled: the first requirement is to synthesize SMM compounds showing intrinsically high T B in the bulk. The second requires implementation of the appropriate methods for molecular deposition on substrates, which provide sufficient decoupling of the SMM from the surface.In this work we provide experimental evidence on outstanding slow magnetic relaxation in Dy 2 @C 80 (CH 2 Ph) sub-monolayers on a graphene/Ir(111) surface. The Dy 2 @C 80 (CH 2 Ph) molecules deposited by the electrospray deposition method are organized into islands as shown by low-temperature scanning tunneling microscopy (STM) imaging. We explore their magnetic properties by means of X-ray absorption spectroscopy (XAS) and X-ray magnetic circular dichroism (XMCD) measurements. The analysis of the magnetic relaxation behavior of Dy 2 @C 80 (CH 2 Ph) adsorbed on graphene/Ir(111) yields a Single-molecule magnets (SMMs) are among the most promising building blocks for future magnetic data storage or quantum computing applications, owing to magnetic bistability and long magnetic relaxation times. The practical device integration requires realization of 2D surface assemblies of SMMs, where each magnetic unit shows magnetic relaxation being sufficiently slow at application-relevant temperatures. Using X-ray absorption spectroscopy and X-ray magnetic circular dichroism, it is shown that sub-monolayers of Dy ...
Antiferromagnetic materials hold promising prospects in novel types of spintronics applications. Assessing the stability of antiferromagnetic nanostructures against thermal excitations is a crucial aspect of designing devices with a high information density. Here we use theoretical calculations and numerical simulations to determine the mean switching time of antiferromagnetic nanoparticles in the superparamagnetic limit. It is demonstrated that the thermal stability is drastically reduced compared to ferromagnetic particles in the limit of low Gilbert damping, attributed to the exchange enhancement of the attempt frequencies. It is discussed how the system parameters have to be engineered in order to optimize the switching rates in antiferromagnetic nanoparticles.
based complexes emerged, showing high magnetic blocking temperatures, often combined with a sufficient redox stability. [16][17][18] Recent experiments aiming at the investigation of electron transport through individual SMMs involving its magnetic system showed, however, that at least in Ln-based double-decker SMMs 4f-electrons are generally difficult to access owing to their spatial localization and energetic position far away from the Fermi level. [19][20][21][22][23][24][25] Direct addressing of 4f magnetic moments inside molecules via electronic transport would thus require systems with electronic orbitals at feasible energies combined with a certain spatial extend as can be realized for early Ln species [25] or systems with electron states that strongly hybridize with 4f orbitals without altering the peculiar magnetic properties of the magnetic complexes. [26,27] Particularly interesting in this sense are functionalized endohedral dimetallofullerenes incorporating a single-electron bond between two ferromagnetically coupled Ln atoms and representing one of the most promising classes of SMMs at the moment. [28] However, whereas their carbon cage fully absorbs the charge redistribution upon surface deposition, being beneficial for their magnetic stability, [29] their endohedral structure at the same time hinders direct access to the molecular interior, being inevitable in terms of applications. Consequently, no experimental proof has been reported up to now that demonstrates access to their magnetic core in transport measurements.In this work, we focus on the endohedral dimetallofullerene complexes Ln 2 @C 80 (CH 2 Ph), referred to as {Ln 2 } in the following. [30] These molecules consist of a roughly spherical fullerene cage that encapsulates two Ln 3+ ions, see Figure 1a. The two lanthanide ions share a single-electron covalent bond, which is stabilized by adding a CH 2 Ph side group to the C 80 cage. This metal-metal bond results in a strong exchange between the Ln centers in the [Ln 3+ -e -Ln 3+ ] system resulting in exceptional magnetic properties both in the bulk [28] and in sub-monolayers. [31,32] Liu et al. [33] have shown that the Ln-Ln bonding molecular orbital (MO) is split into two components, which are fully spin-polarized and energetically well-separated, with the unoccupied component lying below the cage-based lowest unoccupied MO (LUMO) and being partially localized on the C 80 cage thus being in principle addressable in scanning tunneling microscopy/spectroscopy (STM/STS). A decrease in Chemically robust single-molecule magnets (SMMs) with sufficiently high blocking temperatures T B are among the key building blocks for the realization of molecular spintronic or quantum computing devices. Such device applications require access to the magnetic system of a SMM molecule by means of electronic transport, which primarily depends on the interaction of magnetic orbitals with the electronic states of the metallic electrodes. Scanning tunneling microscopy in combination with ab initio calculations al...
Nanodevices based on hybrid graphene-superconductor structures have recently attracted much attention owing to both fundamental and application aspects. However, atomic-level investigations of proximity-induced superconductivity in graphene, especially on technologically relevant substrates remain rare. Here, the atomic-scale study of electronic properties and the superconducting proximity effect in hydrogen-intercalated single-layer graphene on SiC decorated with epitaxial lead (Pb) islands is reported. The graphene layer is thoroughly characterized by means of Landau level spectroscopy which confirms its quasi-free-standing nature. Scanning tunneling spectroscopy performed at 1.8 K on the graphene layer in the vicinity of Pb islands shows a reduced superconducting gap of gr = 0.20(1) meV, which points to a graphene/superconductor junction of moderate transparency. The variations of the proximity-induced superconducting gap on graphene are measured as function of spatial position as well as of magnetic field strength. Spatially resolved measurements yield a coherence length of about 175 nm in the graphene monolayer. The study provides a foundation for realization of graphene-superconductor heterostructures on large-scale SiC(0001) wafers suitable for future technological applications.
In article number 2000082, Fabian Paschke, Mikhail Fonin and co‐workers report on the atomic‐scale study of electronic properties and the superconducting proximity effect in hydrogen‐intercalated graphene on SiC decorated with epitaxial lead (Pb) islands. Scanning tunneling spectroscopy confirms a quasi‐free‐standing nature of the graphene layer. The variations of the proximity‐induced superconducting gap on graphene are measured as function of spatial position as well as of magnetic field strength. The findings of this study pave the way for the large‐scale fabrication of graphene–superconductor heterostructures, which can be implemented for quantum information processing.
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