Search

The on-surface synthesis of nano-graphenes has led the charge in prototyping structures with perspectives beyond silicon-based technology. Following reports of open-shell systems in graphene-nanoribbons (GNR), a flurry of research activities is directed at investigating their magnetic properties with a keen eye for spintronic applications. Although the synthesis of nano-graphenes is usually straightforward on gold, it is difficult to use it for electronic decoupling and spin-polarized measurements. Using a binary alloy Cu3Au(111), we show how to combine the efficient gold-like nano-graphene formation with spin polarization and electronic decoupling known from copper. We prepare copper oxide layers, demonstrate thermally and tip-assisted synthesis of GNR and grow thermally stable magnetic Co islands. We functionalize the tip of a scanning tunneling microscope with carbon-monoxide, nickelocene, or attach Co clusters for high-resolution imaging, magnetic sensing, or spin-polarized measurements. This versatile platform will be a valuable tool in the advanced study of magnetic nano-graphenes.

The current-driven motion of skyrmions in MnSi and FeGe thinned single crystals could be initiated at current densities of the order of 106 A/m2, five orders of magnitude smaller than for magnetic domain walls. The technologically crucial step of replicating these results in thin films has not been successful to-date, but the reasons are not clear. Elucidating them requires analyzing system characteristics at scales of few nm where the key Dzyaloshinskii-Moriya (DM) interactions vary, and doing so in near-application conditions, i.e. in systems at room temperature, capped with additional layers for oxidation protection. In this work’s magnetic force microscopy (MFM) studies of magnetron-sputtered Ir/Co/Pt-multilayers we show skyrmions that are smaller than previously observed, are not circularly symmetric, and are pinned to 50-nm wide areas where the DM interaction is higher than average. This finding matches our measurement of inhomogeneity of the magnetic moment areal density, which amounts to a standard deviation of the Co layer thickness of 0.3 monolayers in our 0.6 nm thick Co layers. This likely originates in small Co layer thickness variation and alloying. These film characteristics must be controlled with greater precision to preclude skyrmion pinning.

The quantum Hall (QH) effect, a topologically non-trivial quantum phase, expanded the concept of topological order in physics bringing into focus the intimate relation between the “bulk” topology and the edge states. The QH effect in graphene is distinguished by its four-fold degenerate zero energy Landau level (zLL), where the symmetry is broken by electron interactions on top of lattice-scale potentials. However, the broken-symmetry edge states have eluded spatial measurements. In this article, we spatially map the quantum Hall broken-symmetry edge states comprising the graphene zLL at integer filling factors of \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${{\nu }}={{0}},\pm {{1}}$$\end{document}ν=0,±1 across the quantum Hall edge boundary using high-resolution atomic force microscopy (AFM) and show a gapped ground state proceeding from the bulk through to the QH edge boundary. Measurements of the chemical potential resolve the energies of the four-fold degenerate zLL as a function of magnetic field and show the interplay of the moiré superlattice potential of the graphene/boron nitride system and spin/valley symmetry-breaking effects in large magnetic fields., The broken-symmetry edge states that are the hallmark of the quantum Hall effect in graphene have eluded spatial measurements. Here, the authors spatially map the quantum Hall broken-symmetry edge states using atomic force microscopy and show a gapped ground state proceeding from the bulk through to the quantum Hall edge boundary.

Mallinson's idea that some spin textures in planar magnetic structures could produce an enhancement of the magnetic flux on one side of the plane at the expense of the other gave rise to permanent magnet configurations known as Halbach magnet arrays. Applications range from wiggler magnets in particle accelerators and free electron lasers to motors and magnetic levitation trains, but exploiting Halbach arrays in micro- or nanoscale spintronics devices requires solving the problem of fabrication and field metrology below a 100 μm size. In this work, we show that a Halbach configuration of moments can be obtained over areas as small as 1 μm × 1 μm in sputtered thin films with Néel-type domain walls of unique domain wall chirality, and we measure their stray field at a controlled probe-sample distance of 12.0 ± 0.5 nm. Because here chirality is determined by the interfacial Dyzaloshinkii-Moriya interaction, the field attenuation and amplification is an intrinsic property of this film, allowing for flexibility of design based on an appropriate definition of magnetic domains. Skyrmions (100 nm wide) illustrate the smallest kind of such structures, for which our measurement of stray magnetic fields and mapping of the spin structure shows they funnel the field toward one specific side of the film given by the sign of the Dyzaloshinkii-Moriya interaction parameter D.

Research in new quantum materials requires multi-mode measurements spanning length scales, correlations of atomic-scale variables with macroscopic function, and spectroscopic energy resolution obtainable only at millikelvin temperatures, typically in a dilution refrigerator. In this article, we describe a multi-mode instrument achieving μeV tunneling resolution with in-operando measurement capabilities of scanning tunneling microscopy (STM), atomic force microscopy (AFM), and magnetotransport inside a dilution refrigerator operating at 10 mK. We describe the system in detail including a new scanning probe microscope module design, sample and tip transport systems, along with wiring, radio-frequency (RF) filtering, and electronics. Extensive benchmarking measurements were performed using superconductor-insulator-superconductor (SIS) tunnel junctions, with Josephson tunneling as a noise metering detector. After extensive testing and optimization, we have achieved less than 8 μeV instrument resolving capability for tunneling spectroscopy, which is 5-10 times better than previous instrument reports and comparable to the quantum and thermal limits set by the operating temperature at 10 mK.

A single-passage, bimodal magnetic force microscopy technique optimized for scanning samples with arbitrary topography is discussed. A double phase-locked loop (PLL) system is used to mechanically excite a high quality factor cantilever under vacuum conditions on its first mode and via an oscillatory tip-sample potential on its second mode. The obtained second mode oscillation amplitude is then used as a proxy for the tip-sample distance, and for the control thereof. With appropriate $z$-feedback parameters two data sets reflecting the magnetic tip-sample interaction and the sample topography are simultaneously obtained., Comment: 4 Pages, 4 Figures

Équipe 101 : Nanomagnétisme et électronique de spin; International audience; We fabricated a perpendicularly magnetized bit pattern media using a hexagonally close-packed auto-assembled anodic alumina template with 100 nm and 50 nm periods by depositing a Co/Pt multilayer to form an ordered array of ferromagnetic nanodots, so-called nanobumps. We used Hall resistance measurements and magnetic force microscopy to characterize the dot-by-dot magnetization reversal mechanism under applied field. The role of interdot exchange coupling and dipolar coupling are investigated. Then we focus on separating the various origins of switching field distribution (SFD) in this system, namely dipolar interactions, intrinsic anisotropy distribution, and template packing faults. Finally we discuss the influence of triangular dipolar frustrations on the energy stability of demagnetized and half-switched states based on an Ising model, including local exchange coupling. The impact of SFD and lattice defects lines between misoriented ordered domains on the magnetic configurations is studied in detail.

We present experimental results and theoretical simulations of the adsorption behavior of the metal-organic precursor Co2(CO)8 on SiO2 surfaces after application of two different pre-treatment steps, namely by air plasma cleaning or a focused electron beam pre-irradiation. We observe a spontaneous dissociation of the precursor molecules as well as auto-deposition of cobalt on the pre-treated SiO2 surfaces. We also find that the differences in metal content and relative stability of these deposits depend on the pre-treatment conditions of the substrate. Transport measurements of these deposits are also presented. We are led to assume that the degree of passivation of the SiO2 surface by hydroxyl groups is an important controlling factor in the dissociation process. Our calculations of various slab settings using dispersion corrected density functional theory support this assumption. We observe physisorption of the precursor molecule on a fully hydroxylated SiO2 surface (untreated surface) and chemisorption on a partially hydroxylated SiO2 surface (pre-treated surface) with a spontaneous dissociation of the precursor molecule. In view of these calculations, we discuss the origin of this dissociation and the subsequent autocatalysis., Comment: 22 pages, 8 Figures, In Press Article, Beilstein Journal of Nanotechnology, 2012

Hydrogenated indium oxide (IOH) is implemented as transparent front contact in Cu(In,Ga)Se2 (CIGS) solar cells, leading to an open circuit voltage VOC enhanced by ∼20 mV as compared to reference devices with ZnO:Al (AZO) electrodes. This effect is reproducible in a wide range of contact sheet resistances corresponding to various IOH thicknesses. We present the detailed electrical characterization of glass/Mo/CIGS/CdS/intrinsic ZnO (i-ZnO)/transparent conductive oxide (TCO) with different IOH/AZO ratios in the front TCO contact in order to identify possible reasons for the enhanced VOC. Temperature and illumination intensity-dependent current-voltage measurements indicate that the dominant recombination path does not change when AZO is replaced by IOH, and it is mainly limited to recombination in the space charge region and at the junction interface of the solar cell. The main finding is that the introduction of even a 5 nm-thin IOH layer at the i-ZnO/TCO interface already results in a step-like increase i...

Actuation and control of motion in micromechanical systems are technological challenges, since they are accompanied by mechanical friction and wear, principal and well-known sources of device lifetime reduction. In this theoretical work we propose a non-contact motion control technique based on the introduction of a tunable magnetic interaction. The latter is realized by coating two non-touching sliding bodies with ferromagnetic films. The resulting dynamics is determined by shape, size and ordering of magnetic domains arising in the films below the Curie temperature. We demonstrate that the domain behavior can be tailored by acting on handles like ferromagnetic coating preparation, external magnetic fields and the finite distance between the plates. In this way, motion control can be achieved without mechanical contact. Moreover, we discuss how such handles can disclose a variety of sliding regimes. Finally, we propose how to practically implement the proposed model sliding system.

A bimodal magnetic force microscopy technique optimized for lateral resolution and sensitivity for small magnetic stray fields is discussed. A double phase-locked loop (PLL) system is used to drive a high-quality factor cantilever under vacuum conditions on its first mode and simultaneously on its second mode. The higher-stiffness second mode is used to map the topography. The magnetic force is measured with the higher-sensitivity first oscillation mode.