18 research outputs found
Induction Mapping of the 3D-Modulated Spin Texture of Skyrmions in Thin Helimagnets
Envisaged applications of skyrmions in magnetic memory and logic devices
crucially depend on the stability and mobility of these topologically
non-trivial magnetic textures in thin films. We present for the first time
quantitative maps of the magnetic induction that provide evidence for a 3D
modulation of the skyrmionic spin texture. The projected in-plane magnetic
induction maps as determined from in-line and off-axis electron holography
carry the clear signature of Bloch skyrmions. However, the magnitude of this
induction is much smaller than the values expected for homogeneous Bloch
skyrmions that extend throughout the thickness of the film. This finding can
only be understood, if the underlying spin textures are modulated along the
out-of-plane z direction. The projection of (the in-plane magnetic induction
of) helices is further found to exhibit thickness-dependent lateral shifts,
which show that this z modulation is accompanied by an (in-plane) modulation
along the x and y directions
Electrical Probing of Field-Driven Cascading Quantized Transitions of Skyrmion Cluster States in MnSi Nanowires
Magnetic skyrmions are topologically stable whirlpool-like spin textures that
offer great promise as information carriers for future ultra-dense memory and
logic devices1-4. To enable such applications, particular attention has been
focused on the skyrmions properties in highly confined geometry such as one
dimensional nanowires5-8. Hitherto it is still experimentally unclear what
happens when the width of the nanowire is comparable to that of a single
skyrmion. Here we report the experimental demonstration of such scheme, where
magnetic field-driven skyrmion cluster (SC) states with small numbers of
skyrmions were demonstrated to exist on the cross-sections of ultra-narrow
single-crystal MnSi nanowires (NWs) with diameters, comparable to the skyrmion
lattice constant (18 nm). In contrast to the skyrmion lattice in bulk MnSi
samples, the skyrmion clusters lead to anomalous magnetoresistance (MR)
behavior measured under magnetic field parallel to the NW long axis, where
quantized jumps in MR are observed and directly associated with the change of
the skyrmion number in the cluster, which is supported by Monte Carlo
simulations. These jumps show the key difference between the clustering and
crystalline states of skyrmions, and lay a solid foundation to realize
skyrmion-based memory devices that the number of skyrmions can be counted via
conventional electrical measurements
Insights and approaches for mapping soil organic carbon as a dynamic soil property
Soil organic C (SOC) content is one of the most dynamic of soil properties. In this study, we examined the effects of land use change on SOC pools for a single soil series and developed a mapping approach to relate SOC dynamics to land use change. Six paired sites, consisting of adjacent agricultural field and forest within a single delineation, were sampled and the SOC pools determined. The average forest SOC pool (157 Mg ha-1) was significantly higher (P \u3c 0.05) than the field pool (103 Mg ha-1), supporting the importance of land use on SOC pools. We propose the development of a SOC phase based on land use to map such differences. Master O and A horizon data should be used to establish SOC phases. Data can be obtained from existing soil surveys, updates, or C accounting activities. Land use classes can be identified with digital imagery and SOC phases can be assigned to all mapping units. Mapping units sampled for C accounting can be resampled to detect patterns and rates of change. This approach provides a robust data set to effectively map and model SOC pools and change across the landscape. © Soil Science Society of America, 5585 Guilford Rd., Madison WI 53711 USA All rights reserved
Chemical Pressure Stabilization of the Cubic B20 Structure in Skyrmion Hosting Fe<sub>1–<i>x</i></sub>Co<sub><i>x</i></sub>Ge Alloys
Iron
monogermanide (FeGe) with the noncentrosymmetric cubic B20
structure is a well-known helimagnet and a magnetic skyrmion host
with a relatively high ordering temperature (∼280 K). FeGe
and related metal monogermanide compounds, such as CoGe and MnGe,
have several structural polymorphs and typically require high pressure
(∼4 GPa) and high temperature (∼1000 °C) to synthesize
in the cubic B20 structure. Here, we report that the cubic B20 phase
of both FeGe and alloys of Fe<sub>1–<i>x</i></sub>Co<sub><i>x</i></sub>Ge could in fact be formed without
the application of high pressure by simply reacting elemental powders
at modest temperatures (550 °C). Furthermore, the incorporation
of Co into Fe<sub>1–<i>x</i></sub>Co<sub><i>x</i></sub>Ge (0.05 ≤ <i>x</i> ≤ 0.1)
stabilizes the cubic B20 structure up to 650 °C, which we propose
is caused by chemical pressure induced by the incorporation of Co
into the lattice. Interestingly, chemical vapor transport reactions
using the Fe<sub>1–<i>x</i></sub>Co<sub><i>x</i></sub>Ge alloys as precursors yield plentiful growth of large (0.1
to 1 mm) single crystals of pure FeGe. Magnetic susceptibility measurements
of the Fe<sub>0.95</sub>Co<sub>0.05</sub>Ge alloy show evidence of
a skyrmion phase not previously reported in the Fe<sub>1–<i>x</i></sub>Co<sub><i>x</i></sub>Ge system
Selective Chemical Vapor Deposition Growth of Cubic FeGe Nanowires That Support Stabilized Magnetic Skyrmions
Magnetic
skyrmions are topologically stable vortex-like spin structures that
are promising for next generation information storage applications.
Materials that host magnetic skyrmions, such as MnSi and FeGe with
the noncentrosymmetric cubic B20 crystal structure, have been shown
to stabilize skyrmions upon nanostructuring. Here, we report a chemical
vapor deposition method to selectively grow nanowires (NWs) of cubic
FeGe out of three possible FeGe polymorphs for the first time using
finely ground particles of cubic FeGe as seeds. X-ray diffraction
and transmission electron microscopy (TEM) confirm that these micron-length
NWs with ∼100 nm to 1 μm diameters have the cubic B20
crystal structure. Although Fe<sub>13</sub>Ge<sub>8</sub> NWs are
also formed, the two types of NWs can be readily differentiated by
their faceting. Lorentz TEM imaging of the cubic FeGe NWs reveals
a skyrmion lattice phase under small applied magnetic fields (∼0.1
T) at 233 K, a skyrmion chain state at lower temperatures (95 K) and
under high magnetic fields (∼0.4 T), and a larger skyrmion
stability window than bulk FeGe. This synthetic approach to cubic
FeGe NWs that support stabilized skyrmions opens a route toward the
exploration of new skyrmion physics and devices based on similar nanostructures