V. T. Volkov

Fabrication and use of a nanoscale Hall probe for measurements of the magnetic field induced by MFM tips

Extraordinary Hall effect probes with 160xa0nm × 160xa0nm working area were fabricated using photo-xa0and electron-beam lithographic procedures with the aim of direct measurements of MFM cantilever tip magnetic properties. The magnetic field sensitivity of the probes was 35xa0Ωxa0T(-1). Magnetic induction of the MFM cantilever tips coated by Co and SmCo films was measured with the probes. It was shown that the resolution of the probes was of the order of 10xa0nm.

Ballistic edge states in Bismuth nanowires revealed by SQUID interferometry

The protection against backscattering provided by topology is a striking property. In two-dimensional insulators, a consequence of this topological protection is the ballistic nature of the one-dimensional helical edge states. One demonstration of ballisticity is the quantized Hall conductance. Here we provide another demonstration of ballistic transport, in the way the edge states carry a supercurrent. The system we have investigated is a micrometre-long monocrystalline bismuth nanowire with topological surfaces, that we connect to two superconducting electrodes. We have measured the relation between the Josephson current flowing through the nanowire and the superconducting phase difference at its ends, the current–phase relation. The sharp sawtooth-shaped phase-modulated current–phase relation we find demonstrates that transport occurs selectively along two ballistic edges of the nanowire. In addition, we show that a magnetic field induces 0–π transitions and φ0-junction behaviour, providing a way to manipulate the phase of the supercurrent-carrying edge states and generate spin supercurrents.

Peculiarities of the extraordinary Hall effect of planar arrays Fe nanoparticles embedded in an ultrathin Pt film

The extraordinary Hall effect was investigated for planar arrays Fe nanoparticles embedded in an ultrathin Pt matrix. It was found that the slope of Hall resistance (RH) reversed sign at ±0.15T for Fe particles of mean thickness 0.3nm. The dependence is presumably due to the effect of two spin-orbital induced mechanisms of carriers scattering, skew scattering, and side jump, with the skew component of positive sign and the side jump component of negative sign. For Fe samples, 0.6nm thick RH increases monotonically with the magnetic field value. At low temperatures, the superparamagnetism of the samples disappeared.

Extraordinary Hall effect in planar ensembles of Co nanoparticles embedded in Au or W

An experimental investigation is presented into the extraordinary Hall effect (EHE) in planar ensembles of Co nanoparticles embedded in a W or Au matrix. The EHE signal strength is shown to depend on the mean thicknesses of both the nanoparticles and the matrix. Its maximum is observed for mean Co thicknesses of 0.3–0.6 nm. The EHE signal is found to grow with decreasing matrix thickness until the structure loses its electrical continuity. A sensitivity as high as S = 32 Θ/T (S = ΔU/IΔH) is achieved with a Co-W film. This result opens up possibilities for building room-temperature ferromagnetic sensors for local magnetometry.

One-Step Synthesis of a Hybrid of Graphene Films and Ribbons

Hybrid structures composed of graphene films and (0001) graphene ribbons perpendicular to the surface of a graphene-like film have been produced through the catalytic decomposition of a carbon-containing gas on an Al-coated SiO2/Si substrate having Ni catalyst islands on its surface. A hybrid structure has been grown by a one-step chemical vapor deposition process, by admitting acetylene into a chamber for a short time. The hybrid structures thus produced have been used to fabricate Hall sensors with a sensitivity of 3000 Ω/T. The synthesized hybrid structures are potential candidates for use in nanoelectronic devices, energy storage systems, etc. The technique proposed for the growth of such films is compatible with technologies that are employed in the electronics industry.

Using a nanoscale extraordinary hall effect sensor to measure the tip field of a magnetic cantilever

The spatial distribution of the magnetic field around the tip of a magnetic cantilever coated with a cobalt film 50 nm thick is investigated using an FePt extraordinary Hall effect sensor. The magnetic field’s dependence on the distance between the sensor’s surface and the MFM cantilever is measured and found to be inversely proportional to the cubic distance, as predicted in theory. The magnetic field measured on the MFM cantilever tip is found to be 0.02 T.

Proximity induced and intrinsic superconductivity in long and short molecules

Publisher Summary This chapter explains the proximity-induced superconductivity that has emerged as one of the most efficient tools of the investigation of phase coherent transport at mesoscopic or nanoscopic scales. Observing proximity effect in long molecular wires implies indeed not only that these molecules are conducting and form a low-resistance contact with superconducting electrodes, but also, which is more fundamental, that both the thermal length and the phase coherence length are of the order of the length of the molecules. The observation of the proximity effect yields the order of the magnitude of typical time- and length-scales involved in the charge transfer mechanism along the molecules. Conductivity measurements on double-stranded DNA molecules deposited by a combing process across a submicron slit between rhenium carbon metallic contacts have been conducted. In the case of carbon nanotubes on superconducting contacts, the observation of high supercurrents strongly suggests the existence of intrinsic superconducting fluctuations. This is corroborated by experiments on long ropes of carbon nanotubes on normal contacts.

Superconductivity in Long and Short Molecules

We present the results of experimental study of superconductivity in individual molecules of carbon nanotubes, DNAs and metallofullerenes. Critical currents of supeconductor‐molecule‐superconductor junctions were extensively studied as a function of temperature and magnetic field. The mechanism of current induced superconductor‐normal state transition for a long molecule (carbon nanotubes and DNAs) is the creation of phase slip centres and for a short molecule (metallofullerens) — multiple Andreev reflections. We observe an influence of spin state of encapsulated atom on the induced superconductvity in a metallofullerene molecule.