1,552 research outputs found
Integrating all-optical switching with spintronics
All-optical switching (AOS) of magnetic materials describes the reversal of
the magnetization using short (femtosecond) laser pulses, and has been observed
in a variety of materials. In the past decade it received extensive attention
due to its high potential for fast and energy-efficient data writing in future
spintronic memory applications. Unfortunately, the AOS mechanism in the
ferromagnetic multilayers commonly used in spintronics needs multiple pulses
for the magnetization reversal, losing its speed and energy efficiency. Here,
we experimentally demonstrate `on-the-fly' single-pulse AOS in combination with
spin Hall effect (SHE) driven motion of magnetic domains in Pt/Co/Gd
synthetic-ferrimagnetic racetracks. Moreover, using field-driven-SHE-assisted
domain wall (DW) motion measurements, both the SHE efficiency in the racetrack
is determined and the chirality of the optically written DW's is verified. Our
experiments demonstrate that Pt/Co/Gd racetracks facilitate both single-pulse
AOS as well as efficient SHE induced domain wall motion, which might ultimately
pave the way towards integrated photonic memory devices
Correlation between magnetism and spin-dependent transport in CoFeB alloys
We report a correlation between the spin polarization of the tunneling
electrons (TSP) and the magnetic moment of amorphous CoFeB alloys. Such a
correlation is surprising since the TSP involves s-like electrons close to the
Fermi level (EF), while the magnetic moment mainly arises due to all
d-electrons below EF. We show that probing the s and d-bands individually
provides clear and crucial evidence for such a correlation to exist through s-d
hybridization, and demonstrate the tuneability of the electronic and magnetic
properties of CoFeB alloys.Comment: Accepted for publication in Physical Review Letters. Letter (4 pages)
and Supplementary material (4 pages
Spin motive forces due to magnetic vortices and domain walls
We study spin motive forces, i.e, spin-dependent forces, and voltages induced
by time-dependent magnetization textures, for moving magnetic vortices and
domain walls. First, we consider the voltage generated by a one-dimensional
field-driven domain wall. Next, we perform detailed calculations on
field-driven vortex domain walls. We find that the results for the voltage as a
function of magnetic field differ between the one-dimensional and vortex domain
wall. For the experimentally relevant case of a vortex domain wall, the
dependence of voltage on field around Walker breakdown depends qualitatively on
the ratio of the so-called -parameter to the Gilbert damping constant,
and thus provides a way to determine this ratio experimentally. We also
consider vortices on a magnetic disk in the presence of an AC magnetic field.
In this case, the phase difference between field and voltage on the edge is
determined by the parameter, providing another experimental method to
determine this quantity.Comment: 8 pages, 9 figures, submitted to PR
Optimizing propagating spin wave spectroscopy
The frequency difference between two oppositely propagating spin waves can be
used to probe several interesting magnetic properties, such as the
Dzyaloshinkii-Moriya interaction (DMI). Propagating spin wave spectroscopy is a
technique that is very sensitive to this frequency difference. Here we show
several elements that are important to optimize devices for such a measurement.
We demonstrate that for wide magnetic strips there is a need for de-embedding.
Additionally, for these wide strips there is a large parasitic antenna-antenna
coupling that obfuscates any spin wave transmission signal, which is remedied
by moving to smaller strips. The conventional antenna design excites spin waves
with two different wave vectors. As the magnetic layers become thinner, the
resulting resonances move closer together and become very difficult to
disentangle. In the last part we therefore propose and verify a new antenna
design that excites spin waves with only one wave vector. We suggest to use
this antenna design to measure the DMI in thin magnetic layers.Comment: 12 pages, 4 figure
Anomalous direction for skyrmion bubble motion
Magnetic skyrmions are localized topological excitations that behave as
particles and can be mobile, with great potential for novel data storage
devices. In this work, the current-induced dynamics of large skyrmion bubbles
is studied. When skyrmion motion in the direction opposite to the electron flow
is observed, this is usually interpreted as a perpendicular spin current
generated by the spin Hall effect exerting a torque on the chiral N\'{e}el
skyrmion. By designing samples in which the direction of the net generated spin
current can be carefully controlled, we surprisingly show that skyrmion motion
is always against the electron flow, irrespective of the net vertical
spin-current direction. We find that a negative bulk spin-transfer torque is
the most plausible explanation for the observed results, which is qualitatively
justified by a simple model that captures the essential behaviour. These
findings demonstrate that claims about the skyrmion chirality based on their
current-induced motion should be taken with great caution
Thickness dependence of unidirectional spin-Hall magnetoresistance in metallic bilayers
A nonlinear magnetoresistance - called unidirectional spin-Hall
magnetoresistance - is recently experimentally discovered in metallic bilayers
consisting of a heavy metal and a ferromagnetic metal. To study the fundamental
mechanism of the USMR, both ferromagnetic and heavy metallic layer thickness
dependence of the USMR are presented in a Pt/Co/AlOx trilayer at room
temperature. To avoid ambiguities, second harmonic Hall measurements are used
for separating spin-Hall and thermal contributions to the non-linear
magnetoresistance. The experimental results are fitted by using a
drift-diffusion theory, with parameters extracted from an analysis of
longitudinal resistivity of the Co layer within the framework of the
Fuchs-Sondheimer model. A good agreement with the theory is found,
demonstrating that the USMR is governed by both the spin-Hall effect in the
heavy metallic layer and the metallic diffusion process in the ferromagnetic
layer
Efficient Gold(I) Acyclic Diaminocarbenes for the Synthesis of Propargylamines and Indolizines
Mononuclear gold(I) acyclic diaminocarbenes (ADCs) were prepared by the reaction of 1, 2-cyclohexanediamine with the corresponding isocyanide complexes [AuCl(CNR)] (R = Cy, tBu). The three-component coupling of aldehydes, amines, and alkynes was investigated by using these gold(I) ADC complexes. The new gold(I) metal complexes are highly efficient catalysts for the synthesis of propargylamines and indolizines in the absence of solvent and in mild conditions. This method affords the corresponding final products with excellent yields in short reaction times. Additionally, chiral gold(I) complexes with ADCs have been prepared and tried in the enantioselective synthesis of propargylamines
Substrate conformal imprint fabrication process of synthetic antiferromagnetic nanoplatelets
Methods to fabricate and characterize monodisperse magnetic nanoplatelets for
fluid/bio-based applications based on spintronic thin-film principles are a
challenge. This is due to the required top-down approach where the transfer of
optimized blanket films to free particles in a fluid while preserving the
magnetic properties is an uncharted field. Here, we explore the use of
substrate conformal imprint lithography (SCIL) as a fast and cost-effective
fabrication route. We analyze the size distribution of nominal 1.8 um and 120
nm diameter platelets and show the effect of the fabrication steps on the
magnetic properties which we explain through changes in the dominant
magnetization reversal mechanism as the size decreases. We show that SCIL
allows for efficient large-scale platelet fabrication and discuss how
application-specific requirements can be solved via process and material
engineering
Magnetotransport properties of iron microwires fabricated by focused electron beam induced autocatalytic growth
We have prepared iron microwires in a combination of focused electron beam
induced deposition (FEBID) and autocatalytic growth from the iron
pentacarbonyl, Fe(CO)5, precursor gas under UHV conditions. The electrical
transport properties of the microwires were investigated and it was found that
the temperature dependence of the longitudinal resistivity (rhoxx) shows a
typical metallic behaviour with a room temperature value of about 88
micro{\Omega} cm. In order to investigate the magnetotransport properties we
have measured the isothermal Hall-resistivities in the range between 4.2 K and
260 K. From these measurements positive values for the ordinary and the
anomalous Hall coefficients were derived. The relation between anomalous Hall
resistivity (rhoAN) and longitudinal resistivity is quadratic, rhoAN rho^2 xx,
revealing an intrinsic origin of the anomalous Hall effect. Finally, at low
temperature in the transversal geometry a negative magnetoresistance of about
0.2 % was measured
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