223 research outputs found
Current-induced Pinwheel Oscillations in Perpendicular Magnetic Anisotropy Spin Valve Nanopillars
Nanopillar spin valve devices are typically comprised of two ferromagnetic
layers: a reference layer and a free layer whose magnetic orientation can be
changed by both an external magnetic field and through the introduction of
spin-polarized electric current. Here we report the continuous repeated
switching behavior of both the reference and free layers of a perpendicular
spin valve made of Co/Pd and Co/Ni multilayers that arises for sufficiently
large DC currents. This periodic switching of the two layers produces an
oscillating signal in the MHz regime but is only observed for one sign of the
applied current. The observed behavior agrees well with micromagnetic
simulations
A COMPARISON OF THE ECONOMIC RENT AND CONSUMER SURPLUS METHODS OF VALUING RECREATION BOATING SITES
Resource /Energy Economics and Policy,
Spin-orbit torque induced dipole skyrmion motion at room temperature
We demonstrate deterministic control of dipole-field-stabilized skyrmions by
means of spin-orbit torques arising from heavy transition-metal seed layers.
Experiments are performed on amorphous Fe/Gd multilayers that are patterned
into wires and exhibit stripe domains and dipole skyrmions at room temperature.
We show that while the domain walls and skyrmions are achiral on average due to
lack of Dzyaloshinskii-Moriya interactions, the N\'eel-like closure domain
walls at each surface are chiral and can couple to spin-orbit torques. The
current-induced domain evolutions are reported for different magnetic phases,
including disordered stripe domains, coexisting stripes and dipole skyrmions
and a closed packed dipole skyrmion lattice. The magnetic textures exhibit
motion under current excitations with a current density ~10^8 A/m2. By
comparing the motion resulting from magnetic spin textures in Fe/Gd films with
different heavy transition-metal interfaces, we confirm spin currents can be
used to manipulate achiral dipole skyrmions via spin-orbit torques.Comment: 23 pages, 8 figure
Bimodal switching field distributions in all-perpendicular spin-valve nanopillars
Switching field measurements of the free layer element of 75 nm diameter
spin-valve nanopillars reveal a bimodal distribution of switching fields at low
temperatures (below 100 K). This result is inconsistent with a model of thermal
activation over a single perpendicular anisotropy barrier. The correlation
between antiparallel to parallel and parallel to antiparallel switching fields
increases to nearly 50% at low temperatures. This reflects random fluctuation
of the shift of the free layer hysteresis loop between two different
magnitudes, which may originate from changes in the dipole field from the
polarizing layer. The magnitude of the loop shift changes by 25% and is
correlated to transitions of the spin-valve into an antiparallel configuration.Comment: 3 pages, 4 figures. Submitted to JAP for 58th MMM Proceeding
Distortion of the Stoner-Wohlfarth astroid by a spin-polarized current
The Stoner-Wohlfarth astroid is a fundamental object in magnetism. It
separates regions of the magnetic field space with two stable magnetization
equilibria from those with only one stable equilibrium and it characterizes the
magnetization reversal of nano-magnets induced by applied magnetic fields. On
the other hand, it was recently demonstrated that transfer of spin angular
momentum from a spin-polarized current provides an alternative way of switching
the magnetization. Here, we examine the astroid of a nano-magnet with uniaxial
magnetic anisotropy under the combined influence of applied fields and
spin-transfer torques. We find that spin-transfer is most efficient at
modifying the astroid when the external field is applied along the easy-axis of
magnetization. On departing from this situation, a threshold current appears
below which spin-transfer becomes ineffective yielding a current-induced dip in
the astroid along the easy-axis direction. An extension of the Stoner-Wohlfarth
model is outlined which accounts for this phenomenon.Comment: 8 pages, 6 figure
Periodic chiral magnetic domains in single-crystal nickel nanowires
We report on experimental and computational investigations of the domain
structure of ~0.2 x 0.2 x 8 {\mu}m single-crystal Ni nanowires (NWs). The Ni
NWs were grown by a thermal chemical vapor deposition technique that results in
highly-oriented single-crystal structures on amorphous SiOx coated Si
substrates. Magnetoresistance measurements of the Ni NWs suggest the average
magnetization points largely off the NW long axis at zero field. X-ray
photoemission electron microscopy images show a well-defined periodic
magnetization pattern along the surface of the nanowires with a period of
{\lambda} = 250 nm. Finite element micromagnetic simulations reveal that an
oscillatory magnetization configuration with a period closely matching
experimental observation ({\lambda} = 240 nm) is obtainable at remanence. This
magnetization configuration involves a periodic array of alternating chirality
vortex domains distributed along the length of the NW. Vortex formation is
attributable to the cubic anisotropy of the single crystal Ni NW system and its
reduced structural dimensions. The periodic alternating chirality vortex state
is a topologically protected metastable state, analogous to an array of
360{\deg} domain walls in a thin strip. Simulations show that other remanent
states are also possible, depending on the field history. Effects of material
properties and strain on the vortex pattern are investigated. It is shown that
at reduced cubic anisotropy vortices are no longer stable, while negative
uniaxial anisotropy and magnetoelastic effects in the presence of compressive
biaxial strain contribute to vortex formation.Comment: 15 pages, 11 figure
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