A novel method for the injection and manipulation of magnetic charge states in nanostructures

Realising the promise of next-generation magnetic nanotechnologies is contingent on the development of novel methods for controlling magnetic states at the nanoscale. There is currently demand for simple and flexible techniques to access exotic magnetisation states without convoluted fabrication and application processes. 360 degree domain walls (metastable twists in magnetisation separating two domains with parallel magnetisation) are one such state, which is currently of great interest in data storage and magnonics. Here, we demonstrate a straightforward and powerful process whereby a moving magnetic charge, provided experimentally by a magnetic force microscope tip, can write and manipulate magnetic charge states in ferromagnetic nanowires. The method is applicable to a wide range of nanowire architectures with considerable benefits over existing techniques. We confirm the method's efficacy via the injection and spatial manipulation of 360 degree domain walls in Py and Co nanowires. Experimental results are supported by micromagnetic simulations of the tip-nanowire interaction.Comment: in Scientific Reports (2016

Regulation of Gut and Heart Left–Right Asymmetry by Context-Dependent Interactions between Xenopus Lefty and BMP4 Signaling

AbstractThe Lefty subfamily of TGFβ signaling molecules has been implicated in early development in mouse, zebrafish, and chick. Here, we show that Xenopus lefty (Xlefty) is expressed both bilaterally in symmetric midline domains and unilaterally in left lateral plate mesoderm and anterior dorsal endoderm. To examine the roles of Xlefty in left–right development, we created a system for scoring gut asymmetry and examined the effects of unilateral Xlefty misexpression on gut development, heart development, and Xnr-1 and XPitx2 expression. In contrast to the unilateral effects of Vg1, Activin, Nodal, or BMPs, targeted expression of Xlefty in either the left or the right side of Xenopus embryos randomized the direction of heart looping, gut coiling, and left–right positioning of the gut and downregulated the asymmetric expression of Xnr-1 and XPitx2. It is currently thought that Lefty proteins act as feedback inhibitors of Nodal signaling. However, this would not explain the effects of right-sided Xlefty misexpression. Here, we show that Xlefty interacts with the signaling pathways of other members of the TGFβ family during left–right development. Results from coexpression of Xlefty and Vg1 indicate that Xlefty can nullify the effects of Vg1 ectopic expression and that Xlefty is downstream of left-sided Vg1 signaling. Results from coexpression of Xlefty and XBMP4 indicate that XLefty and XBMP4 interact both synergistically and antagonistically in a context-dependent manner. We propose a model in which interactions of Xlefty with multiple members of the TGFβ family enhance the differences between the right-sided BMP/ALK2/Smad pathway and the left-sided Vg1/anti-BMP/Nodal pathway, leading to left–right morphogenesis of the gut and heart

High field magneto-transport in high mobility gated InSb/InAlSb quantum well heterostructures

We present high field magneto-transport data from a range of 30nm wide InSb/InAlSb quantum wells. The low temperature carrier mobility of the samples studied ranged from 18.4 to 39.5 m2V-1s-1 with carrier densities between 1.5x1015 and 3.28x1015 m-2. Room temperature mobilities are reported in excess of 6 m2V-1s-1. It is found that the Landau level broadening decreases with carrier density and beating patterns are observed in the magnetoresistance with non-zero node amplitudes in samples with the narrowest broadening despite the presence of a large g-factor. The beating is attributed to Rashba splitting phenomenon and Rashba coupling parameters are extracted from the difference in spin populations for a range of samples and gate biases. The influence of Landau level broadening and spin-dependent scattering rates on the observation of beating in the Shubnikov-de Haas oscillations is investigated by simulations of the magnetoconductance. Data with non-zero beat node amplitudes are accompanied by asymmetric peaks in the Fourier transform, which are successfully reproduced by introducing a spin-dependent broadening in the simulations. It is found that the low-energy (majority) spin up state suffers more scattering than the high-energy (minority) spin down state and that the absence of beating patterns in the majority of (lower density) samples can be attributed to the same effect when the magnitude of the level broadening is large

CVD of CrO2: towards a lower temperature deposition process

We report on the synthesis of highly oriented a-axis CrO2 films onto (0001) sapphire by atmospheric pressure CVD from CrO3 precursor, at growth temperatures down to 330 degree Celsius, i.e. close to 70 degrees lower than in published data for the same chemical system. The films keep the high quality magnetic behaviour as those deposited at higher temperature, which can be looked as a promising result in view of their use with thermally sensitive materials, e.g. narrow band gap semiconductors.Comment: 13 pages, 4 figure

Structural, magnetic, and transport properties of thin films of the Heusler alloy Co2MnSi

Thin films of Co2MnSi have been grown on a-plane sapphire substrates from three elemental targets by do magnetron cosputtering. These films are single phase, have a strong (110) texture, and a, saturation magnetization of 4.95mu(B)/formula unit at 10 K. Films grown at the highest substrate temperature of 715 K showed the lowest resistivity (47 muOmega cm at 4.2 K) and the lowest coercivity (18 Oe). The spin polarization of the transport current was found to be of the order of 54% as determined by point contact Andreev reflection spectroscopy. A decrease in saturation magnetization with a decrease, in film thickness and different transport behavior in thinner films indicate graded disorder in these films grown on nonlattice matched substrates. (C) 2004 American Institute of Physics

Direct observation and control of magnetic monopole defects in an artificial spin-ice material

Magnetic monopoles have stimulated a great amount of theoretical and experimental interest since their prediction by Dirac in 1931. To date, their presence has evaded detection in high energy experiments despite intensive efforts. Recently, entities that mimic magnetic monopoles have been observed in bulk and planar frustrated materials known as spin-ice materials, and artificial spin-ice materials, respectively. In this paper we discuss the formation of these so-called monopole defects within a cobalt honeycomb artificial spin-ice lattice. Experimental results and micromagnetic simulations show that monopole defects of opposite sign are created at the boundaries of the lattice, and move in opposing directions. Discrepancies between simulations and experimental results demonstrate the importance of quenched disorder. Furthermore, we show that controlled edge nucleated monopole defect formation can be realized with the use of soft magnetic injection pads, which is a very promising development for technological applications based upon magnetic charge

The spin polarization of CrO2 revisited

Here, we use Andreev reflection spectroscopy to study the spin polarization of high quality CrO2 films. We study the spin polarization as a function of growth temperature, resulting in grain size and electrical resistivity. In these films low temperature growth appears to be a necessary but not sufficient condition to guarantee the observation of high spin polarization, and this is only observed in conjunction with suppressed superconducting gap values and anomalously low interface properties. We suggest that this combination of observations is a manifestation of the long range spin triplet proximity effect. (C) 2007 American Institute of Physics