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A new technique is required which enables tailoring of the morphology of a metallic nanostructured material down to the 10 nm length scale. Using nanoporous nuclear track etched membranes as templates for electrodeposition, an assembly of wires with diameters as low as 30 nm could be obtained. Alternating the electrodeposition of two metals resulted in multilayers grown perpendicular to the wire axis. Layer thicknesses as low as 2 nm could be reached. Application is demonstrated by making wires 6 μm long, 80 nm in diameter, having a succession of either Co and Cu layers or of (Ni,Fe) and Cu layers. Wires containing layers of 5–10 nm in thickness exhibited a giant magnetoresistance. The current was naturally perpendicular to the layers. At ambient temperature, a magnetoresistance of 14% for Co/Cu and of 10% for (Fe,Ni)/Cu was observed.

Major breakthroughs have recently been reported that can help overcome two inherent drawbacks of NMR: the lack of sensitivity and the limited memory of longitudinal magnetization. Dynamic nuclear polarization (DNP) couples nuclear spins to the large reservoir of electrons, thus making it possible to detect dilute endogenous substances in magnetic resonance spectroscopy (MRS) and magnetic resonance imaging (MRI). We have designed a method to preserve enhanced (''hyperpolarized'') magnetization by conversion into long-lived states (LLS). It is shown that these enhanced long-lived states can be generated for proton spins, which afford sensitive detection. Even in complex molecules such as peptides, long-lived proton states can be sustained effectively over time intervals on the order of tens of seconds, thus allowing hyperpolarized substrates to reach target areas and affording access to slow metabolic pathways. The natural abundance carbon-13 polarization has been enhanced ex situ by almost four orders of magnitude in the dipeptide Ala-Gly. The sample was transferred by the dissolution process to a high-resolution magnet where the carbon-13 polarization was converted into a long-lived state associated with a pair of protons. In Ala-Gly, the lifetime TLLS associated with the two nonequivalent H ␣ glycine protons, sustained by suitable radio-frequency irradiation, was found to be seven times longer than their spin-lattice relaxation time constant (TLLS/T1 ‫؍‬ 7). At desired intervals, small fractions of the populations of long-lived states were converted into observable magnetization. This opens the way to observing slow chemical reactions and slow transport phenomena such as diffusion by enhanced magnetic resonance.dynamic nuclear polarization ͉ dissolution process ͉ nuclear magnetic resonance ͉ magnetic resonance imaging ͉ metabolic pathways O ne of the many advantages of magnetic resonance (MR) compared with computed tomography (CT) and imaging methods based on radioactive tracers, such as positron emission tomography (PET) or single photon emission computed tomography (SPECT), lies in the ability of MR to determine both the spatial distribution of the substrates and their transformation through metabolic processes. Unfortunately, most applications of magnetic resonance imaging (MRI) techniques are limited to the detection of water, because other substances are not sufficiently abundant. Even with infusion of labeled substrates, chemical shift imaging (CSI) suffers from poor sensitivity. Thus, the potential to differentiate between molecules is often left unused. The sensitivity of magnetic resonance spectroscopy (MRS) and imaging (MRI) may be considerably improved by coupling the nuclear spins to electron spins via dynamic nuclear polarization (DNP) (1). By enhancing the nuclear polarization of selected endogenous substances, one cannot only image their spatial distribution without background signals, but also visualize their metabolic reaction products (2). The use of hyperpolarized substrates to follow metabol...

The effect of pulsed currents on magnetization reversal were studied on single ferromagnetic nanowires of diameter about 80 nm and 6000 nm length. The magnetization reversal in these wires occurs with a jump of the magnetization at the switching field Hsw, which corresponds to unstable states of the magnetization. A pulsed current of about 10 7 A/cm 2 was injected at different values of the applied field close to Hsw. The injected current triggered the magnetization reversal at a value of the applied field distant from the switching field by as much as 20%. This effect of current-induced magnetization reversal is interpreted in terms of the action of the spin-polarized conduction electrons on the magnetization.

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