Fuel‐free nanomotors are essential for future in‐vivo biomedical transport and drug‐delivery applications. Herein, the first example of directed delivery of drug‐loaded magnetic polymeric particles using magnetically driven flexible nanoswimmers is described. It is demonstrated that flexible magnetic nickel–silver nanoswimmers (5–6 μm in length and 200 nm in diameter) are able to transport micrometer particles at high speeds of more than 10 μm s−1 (more than 0.2 body lengths per revolution in dimensionless speed). The fundamental mechanism of the cargo‐towing ability of these magnetic (fuel‐free) nanowire motors is modelled, and the hydrodynamic features of these cargo‐loaded motors discussed. The effect of the cargo size on swimming performance is evaluated experimentally and compared to a theoretical model, emphasizing the interplay between hydrodynamic drag forces and boundary actuation. The latter leads to an unusual increase of the propulsion speed at an intermediate particle size. Potential applications of these cargo‐towing nanoswimmers are demonstrated by using the directed delivery of drug‐loaded microparticles to HeLa cancer cells in biological media. Transport of the drug carriers through a microchannel from the pick‐up zone to the release microwell is further illustrated. It is expected that magnetically driven nanoswimmers will provide a new approach for the rapid delivery of target‐specific drug carriers to predetermined destinations.

Understanding electronic structure at the nanoscale is crucial to untangling fundamental physics puzzles such as phase separation and emergent behavior in complex magnetic oxides. Probes with the ability to see beyond surfaces on nanometer length and subpicosecond time scales can greatly enhance our understanding of these systems and will undoubtedly impact development of future information technologies. Polarized X-rays are an appealing choice of probe due to their penetrating power, elemental and magnetic specificity, and high spatial resolution. The resolution of traditional X-ray microscopes is limited by the nanometer precision required to fabricate X-ray optics. Here we present a novel approach to lensless imaging of an extended magnetic nanostructure, in which a scanned series of dichroic coherent diffraction patterns is recorded and numerically inverted to map its magnetic domain configuration. Unlike holographic methods, it does not require a reference wave or precision optics. In addition, it enables the imaging of samples with arbitrarily large spatial dimensions, at a spatial resolution limited solely by the coherent X-ray flux, wavelength, and stability of the sample with respect to the beam. It can readily be extended to nonmagnetic systems that exhibit circular or linear dichroism. We demonstrate this approach by imaging ferrimagnetic labyrinthine domains in a Gd/Fe multilayer with perpendicular anisotropy and follow the evolution of the domain structure through part of its magnetization hysteresis loop. This approach is scalable to imaging with diffraction-limited resolution, a prospect rapidly becoming a reality in view of the new generation of phenomenally brilliant X-ray sources.magnetism | phase retrieval | lensless imaging | ptychography | X-ray microscopy M aterials such as magnetic multilayers and alloys, polymers, liquid crystals, biofibers, and biominerals all exhibit self-organizing, reaction-diffusion, and pattern-forming behavior not fully understood. New schemes for directed domain formation in magnetic multilayers and alloys are integral parts of next-generation magnetic data storage and spintronic technologies (1, 2). Controlled phase transitions and ordering dynamics in polymers and liquid crystals under applied electric fields, with consequent photonic bandgap shifts, play a major role in organic laser technology (3). In the biological sciences, certain biofibers display tensile properties similar to that of steel yet are far more lightweight, properties thought to be the result of self-organized phase separation of molecular crystalline and amorphous regions within the fibers (4, 5). Deeper understanding of biomineral growth and the interaction between inorganic material and organic macromolecule phases could enable use of similar techniques to fabricate novel synthetic materials.Microscopy using dichroism as a contrast mechanism can reveal much about phase ordering, separation, and coexistence in these kinds of systems. All of these materials have an order parameter that scatte...

We explore the origins of perpendicular magnetic anisotropy in epitaxial and textured Co/Ni (111) superlattices using a combination of thin film growth, structural characterization, x-ray magnetic circular dichroism (XMCD) and ab-initio calculations. Transmission electron microscopy and x-ray diffraction experiments allow us to show that the "bulk" magnetoelastic contribution to the total magnetic energy is small compared to the interface anisotropy. The magnetic properties are studied by using XMCD at the Co and Ni L 2,3 edges. Hysteresis loops performed at the Co L 3 edge confirm the perpendicular magnetization for Co thicknesses up to 4 monolayers. The spin and orbital moments were deduced using the XMCD sum rules. The results are explained by considering two kinds of magnetic moments for Co, distinguishing the interfaces from the rest of the layers. Both effective spin and orbital moments of Co atoms are found to be enhanced at the Co-Ni interfaces, whereas the magnetic moment of Co surrounded by Co is similar to the bulk values. Ab-initio calculations allow us to show a strong enhancement of the dipole operator contribution on Co atoms at the interface that is partly responsible for this high effective spin moment at the interface. Such a moment enhancement is not observed for Ni, the dipole operator contribution being close to zero. Finally, we observed a very surprising proportionality between the effective spin and orbital moments, independent of the absorption edge or deposition technique used. We assign this peculiar behavior to the fact that the magnetic dipole operator involved in the sum rules is closely linked to the increase of the Co orbital moment at the interface. Based on XMCD results obtained on both molecular beam epitaxy and sputter deposited samples, this link allows us to show the extreme sensitivity of the perpendicular anisotropy with the chemical ordering at the interface. 2

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Using the physical process of ultraintense field ionization of high charge states of inert gas ions, we have developed a method of peak intensity measurement at the focus of high energy short pulse lasers operating in single shot mode. The technique involves detecting ionization products created from a low pressure gas target at the laser focus via time of flight detector. The observation of high ion charge states collected by the detector yields peak intensity at the focus when compared with the results obtained from well established tunnel ionization models. An initial peak intensity measurement of 5× 1016 W cm-2 was obtained for a 1.053 μm center wavelength, 0.4 J pulse with 1 ps pulse duration focused with an f5.5 off-axis parabola. Experiments with multijoule level, 500 fs laser pulses are on the way. © 2006 American Institute of Physics