National Nanomanufacturing Network Events 2011

Nanoinformatics 2011 brought together informatics experts, nanotechnology researchers, and other stakeholders and potential contributors to advance Nanoinformatics 2020 Roadmap goals. The workshop will set a clear path for Nanoinformatics participants through the presentation of projects and research, open discussions, and strategic planning sessions. The Nanomanufacturing Summit 2011 – showcased emerging areas of nanomanufacturing and commercialization of nanotechnology-enabled products by leaders in the field of nanomanufacturing

Polarization Dependent Switching of Asymmetric Nanorings with a Circular Field

We experimentally investigated the switching from onion to vortex states in asymmetric cobalt nanorings by an applied circular field. An in-plane field is applied along the symmetric or asymmetric axis of the ring to establish domain walls (DWs) with symmetric or asymmetric polarization. A circular field is then applied to switch from the onion state to the vortex state, moving the DWs in the process. The asymmetry of the ring leads to different switching fields depending on the location of the DWs and direction of applied field. For polarization along the asymmetric axis, the field required to move the DWs to the narrow side of the ring is smaller than the field required to move the DWs to the larger side of the ring. For polarization along the symmetric axis, establishing one DW in the narrow side and one on the wide side, the field required to switch to the vortex state is an intermediate value

Incoherent dynamics of vibrating single-molecule transistors

We study the tunneling conductance of nano-scale quantum ``shuttles'' in connection with a recent experiment (H. Park et al., Nature, 407, 57 (2000)) in which a vibrating C^60 molecule was apparently functioning as the island of a single electron transistor (SET). While our calculation starts from the same model of previous work (D. Boese and H. Schoeller, Europhys. Lett. 54, 66(2001)) we obtain quantitatively different dynamics. Calculated I-V curves exhibit most features present in experimental data with a physically reasonable parameter set, and point to a strong dependence of the oscillator's potential on the electrostatics of the island region. We propose that in a regime where the electric field due to the bias voltage itself affects island position, a "catastrophic" negative differential conductance (NDC) may be realized. This effect is directly attributable to the magnitude of overlap of final and initial quantum oscillator states, and as such represents experimental control over quantum transitions of the oscillator via the macroscopically controllable bias voltage.Comment: 6 pages, LaTex, 6 figure

Energetic Analysis of Magnetic Transitions in Ultra-small Nanoscopic Magnetic Rings

In this article, we report on experimental and theoretical investigations of magnetic transitions in cobalt rings of size (diameter, width and thickness) comparable to the exchange length of cobalt. Magnetization measurements were performed for two sets of magnetic ring arrays: ultra-small magnetic rings (outer diameter 13 nm, inner diameter 5nm and thickness 5 nm) and small thin-walled magnetic rings (outer diameter 150 nm, width 5 nm and thickness 5 nm). This is the first report on the fabrication and magnetic properties of such small rings. Our calculations suggest that if the magnetic ring's sizes are comparable to, or smaller than, the exchange length of the magnetic material, then only two magnetic states are important - the pure single domain state and the flux closure vortex state. The onion-shape magnetic state does not arise. Theoretical calculations are based on an energetic analysis of pure and slightly distorted single domain and flux closure vortex magnetic states. Based on the analytical calculations, a phase diagram is also derived for ultra-small ring structures exhibiting the region for vortex magnetic state formations as a function of material parameter.Comment: 10 pages, 15 figure

Magnetization Vorticity and Exchange Bias Phenomena in Arrays of Small Asymmetric Magnetic Rings

Arrays of nanoscopic magnetic asymmetric rings, 150 nm in outer diameter, are fabricated using the techniques of electron-beam lithography, angular deposition and ion-beam etching. Magnetic measurements for cobalt asymmetric rings at room temperature verifies previous reports of vortex magnetic state formation of a desired circulation direction for the application of external magnetic field along the asymmetry axis of the rings. However, the main theme of this article is the observation of exchange bias phenomena when the ring samples are cooled down to low temperature in the presence of a positive magnetic field. Very interestingly, the observed exchange bias effect is negative for along and perpendicular orientations of ring's asymmetry axis with respect to the in-plane external magnetic field. This is in good quantitative agreement with the random interface model proposed by Malozemoff et al. For the application of inplane external magnetic field at 45 degree with respect to the asymmetry axis, the exchange bias effect is positive. Unlike the exchange bias effects in thin films, this is a very unusual observation indicating that exchange bias phenomena of opposite natures can be manipulated by appropriate combination of geometrical constraint and external magnetic field direction, in addition to the interfacial interactions between ferromagnetic (FM) and antiferromagnetic (AFM) layer.Comment: Asymmetric magnetic rings arrays; Exchange bias phenomen

Fabrication of Flexible Oriented Magnetic Thin Films with Large in-plane Uniaxial Anisotropy by Roll-to-roll Nanoimprint Lithography

Here, we report wafer scale fabrication of densely packed Fe nanostripe-based magnetic thin films on a flexible substrate and their magnetic anisotropy properties. We find that Fe nanostripes exhibit large in-plane uniaxial anisotropy and nearly square hysteresis loops with energy products (BH)max exceeding 3 MGOe at room temperature. High density Fe nanostripes were fabricated on 70 nm flexible polyethylene terephthalate (PET) gratings, which were made by roll-to-roll (R2R) UV nanoimprintlithography technique. Observed large in-plane uniaxial anisotropies along the long dimension of nanostripes are attributed to the shape. Temperature dependent hysteresis measurements confirm that the magnetization reversal is driven by non-coherent rotation reversal processes.Comment: 17 pages, 6 figure