S. N. Gordeev

Giant magnetoresistance by exchange springs in DyFe2/YFe2 superlattices

Magnetization and magnetoresistance measurements are reported for antiferromagnetically coupled DyFe2/YFe2 multilayers in fields up to 23 T. It is demonstrated that the formation of short exchange springs ( ~20 A) in the magnetically soft YFe2 layers results in a giant magnetoresistance as high as 32% in the spring region. It is shown that both the magnitude of the effect and its dependence on magnetic field are in good agreement with the theory of Levy and Zhang for domain wall induced giant magnetoresistance.

Negative coercivity in epitaxially grown (110) DyFe2/YFe2 superlattices

Molecular beam epitaxial methods have been used to grow single crystal Laves phase DyFe2/YFe2 superlattice samples with a (110) growth direction. Detailed magnetization curves have been obtained for YFe2 dominated multilayer samples [wDyFe2/4wYFe2]×16 with w=45, 50, and 55 A. In particular, it is shown that the formation of magnetic exchange springs in the magnetically soft YFe2 layers, can be used to engineer multilayer samples with a negative coercivity. Further, by using asymmetric field cycling procedures, we have investigated the irreversible parts of the M–B loop, associated with the switching of the DyFe2 multilayers.

Nanomechanical electron shuttle consisting of a gold nanoparticle embedded within the gap between two gold electrodes

Nanomechanical shuttles transferring small groups of electrons or even individual electrons from one electrode to another offer a novel approach to the problem of controlled charge transport. Here, we report the fabrication of shuttle-junctions consisting of a 20 nm diameter gold nanoparticle embedded within the gap between two gold electrodes. The nanoparticle is attached to the electrodes through a monolayer of flexible organic molecules which play the role of springs so that when a sufficient voltage bias is applied, then nanoparticle starts to oscillate transferring electrons from one electrode to the other. Current-voltage characteristics for the fabricated devices have been measured and compared with the results of our computer simulations.

Interplay between superconductivity and magnetism in Gd/La superlattices

Abstract A [Gd 30 /La 10 ] 60 superlattice has been studied using SQUID magnetometry and polarised neutron reflectivity. Zero-field cooling results in the coexistence of an antiferromagnetic alignment of the ferromagnetic Gd blocks, and 3D superconductivity at low temperature. Field cooling from room temperature results in ferromagnetic coupling between the Gd blocks, and under these conditions, the superconducting transition in the La is suppressed.

Discrete exchange-springs in magnetic multilayer samples

The properties of soft magnetic exchange-springs in both bilayer and multilayer samples are investigated, with particular emphasis on the discrete nature of the spring. It is shown that, in a mean-field model, a very simple relationship exists between the bending field BB, the exchange field BEX, and the number of monolayers N in the soft magnetic layer. For bilayers BB/BEX = (π/2N)2, whereas for multilayers BB/BEX = (π/N)2. In addition, it is shown that Jacobi elliptic functions, originally used by Goto et al for continuous bilayer springs, provide a surprisingly robust description of discrete bilayer and symmetric multilayer exchange-springs. Finally, the problem of soft exchange-spring penetration into neighbouring hard magnetic layers is discussed. Calculations show that this is an important effect, which leads to a reduction in the bending field BB.

Proximity effects in free-standing EBID structures

Proximity effects causing thickening and bending of closely spaced, free-standing pillars grown by electron-beam-induced deposition are investigated. It is shown that growth of a new pillar induces deposition of a layer of additional material on the side of already grown pillars facing the new pillar. We present experimental results which suggest that the bending of pillars is caused by shrinkage of the newly formed layer on exposure to the primary electron beam.

Characterization of Topical Film-Forming Systems Using Atomic Force Microscopy and Raman Microspectroscopy

Polymeric film-forming systems for dermal drug delivery represent an advantageous alternative to more conventional topically applied formulations. Their mechanical properties and homogeneity can be characterized with atomic force microscopy (AFM), using both imaging and nanoindentation modes, and Raman microspectroscopy mapping. Film-forming polymers, with and without a plasticizer and/or betamethasone 17-valerate (a representative topical drug), were dissolved in absolute ethanol. Polymeric films were then cast on glass slides and examined in ambient air using AFM imaging and Raman microspectroscopy. Using nanoindentation, the elastic moduli of various films were determined and found to decrease with increasing plasticizer content. Films with 20% w/w plasticizer had elastic moduli close to that of skin. AFM images showed little difference in the topography of the films on incorporation of plasticizer. Raman microspectroscopy maps of the surface of the polymeric films, with a spatial resolution of approximately 1 μm, revealed homogeneous distributions of plasticizer and drug within the films.

An atomic force microscope nanoscalpel for nanolithography and biological applications

We present the fabrication of specialized nanotools, termed nanoscalpels, and their application for nanolithography and nanomechanical manipulation of biological objects. Fabricated nanoscalpels have the shape of a thin blade with the controlled thickness of 20-30 nm and width of 100-200 nm. They were fabricated using electron beam induced deposition at the apex of atomic force microscope probes and are hard enough for a single cut to penetrate a approximately 45 nm thick gold layer; and thus can be used for making narrow electrode gaps required for fabrication of nanoelectronic devices. As an atomic force microscope-based technique the nanoscalpel provides simultaneous control of the applied cutting force and the depth of the cut. Using mammalian cells as an example, we demonstrated their ability to make narrow incisions and measurements of local elastic and inelastic characteristics of a cell, making nanoscalpels also useful as a nanosurgical tool in cell biology. Therefore, we believe that the nanoscalpel could serve as an important tool for nanofabrication and nanosurgery on biological objects.

Large flexibility of high aspect ratio carbon nanostructures fabricated by electron-beam-induced deposition

The mechanical properties of free-standing electron beam deposited amorphous carbon structures have been studied using atomic force microscopy. The fabricated carbon blades are found to be extraordinarily flexible, capable of undergoing vertical deflection up to ∼ 75% of their total length without inelastic deformation. The elastic bending modulus of these structures was calculated to be 28 ± 10 GPa.

Comparative AC susceptibility and resistivity studies of the vortex lattice melting transition in detwinned YBa2Cu3O7-δ single crystals

Abstract We have studied the transition from the vortex liquid to the vortex solid state in clean, detwinned YBa2Cu3O7−δ single crystals in fields up to 12 T using AC susceptibility and resistivity measurements. For μ0H 1 , 2 ) was found to be accompanied by an AC field independent abrupt onset of both χ′ and χ″ components. The AC susceptibility data suggest that just below Tm there is a transition region where the liquid and solid phases coexist. The width of the transition region was found to be sample dependent and can be related to structural inhomogeneity. Above the multicritical field μ0Hmc=7 T simultaneous broadening of both the ρ(T) drop and the χ″(T) onset show that the first order melting transition is suppressed.