Titles and Abstracts
The Spin on Electronics!
Stuart Parkin
IBM Almaden
Research Center
Recent
advances in generating, manipulating and detecting spin-polarized
electrons and
electrical current make possible new classes of spin based sensor, memory
and
logic devices. This talk will review recent developments in this field,
especially the physics and applications of magnetic tunnel junctions as
non-volatile memory elements and as solid-state sources of highly spin
polarized current.
How do you design a
sensible
computer?
Robert Garner
IBM Almaden
Research Center
What are the basic, fundamental elements
required to build a universal, general-purpose computer? This tutorial
will
cover the minimum logical elements that need a physical counter part in
any technology
that wishes to efficiently and reliability implement a general-purpose
computer. I'll also discuss a range of efficiencies that may make sense
relative to future microprocessors and touch on some unorthodox logic gate
implementations that were pursued long before FET's became prevalent.
I'll end
with some reflections on qubit and reversible computing.
Spin Electronics and Spin Computation
Sankar Das Sarma
University of Maryland
I will provide an elementary
introduction to the emerging field of spintronics in this talk. Active
control
of carrier spin in nanostructures of semiconductors and other electronic
materials
is projected to lead to new device functionalities in the future. In
particular, it may be possible to envision memory and logic operations
being
carried out on the same 'spintronic' chip. I will discuss various aspects
of
fundamental physics related to this new research area of spin electronics
with
the particular emphasis on spin-polarized transport and spin electronic
materials (e.g. ferromagnetic semiconductors). A revolutionary possibility
in
the (perhaps, far) future is using the natural two-level dynamics of
electron
spin to create robust quantum bits ('qubits') which could be used to carry
out
solid state quantum information processing or quantum computation. I will
discuss the issues of entanglement, decoherence, quantum error correction,
and
quantum gates in semiconductor nanostructure-based solid state spin
quantum
computer architectures.
Please see http://www.physics.umd.edu/cmtc
for more information about spintronics and related references.
(Theoretical) Spintronics with Ferromagnetic
Semiconductors
Allan MacDonald
University of Texas, Austin
Spintronics in semiconductors can be based
on
the creation and manipulation of spin-polarized currents by injection from
metallic ferromagnets, by optical orientation, by combining spin-orbit
coupling
and electrical control, by Zeeman coupling, or by exploiting
ferromagnetism in
semiconductor materials. Useful spintronics effects will likely require a
relatively abrupt dependence of a readily measurable properties on an
easily
controllable parameters. Among the possibilities for spin-control listed
above, ferromagnetism in semiconductors has many appealing advantages.
The
problem is that ferromagnetism at room temperature has not yet been
demonstrated.
With this in mind I will present a personal view on the prospects for room
temperature ferromagnetism in a well understood semiconductor. I will
also
discuss a new effect in which the transition temperature of a ferromagnet
abruptly changes by a factor of two as a function of a gate voltage. This
effect illustrates the potential of ferromagnetic
semiconductors.
X-Ray Studies of Materials
and
Processes in Spintronics
Joachim Stöhr
Stanford
Synchrotron Radiation Laboratory,
Stanford,
CA 94309
I will give an overview of state-of-the-art x-ray
dichroism
techniques, both spectroscopy and microscopy, which have been developed
over
the last 15 years for the study of magnetic materials and phenomena. I
will
show how these techniques can be used to study complex nanoscale magnetic
materials and their magnetization dynamics. As examples I will discuss the
use
of x-ray techniques to study the layer-by-layer magnetic structure in
ferromagnets
and antiferromagnets, interfacial magnetic phenomena, the time-resolved
response of magnetic nanostructures to sub-nanosecond magnetic field
pulses,
and magnetic switching phenomena due to spin polarized currents. I will
finish
with my personal vision of future uses of x-ray for studies of the
ultrafast
magnetic nanoworld.
Ultrafast magnetization dynamics
triggered
by magnetic field pulses
Hans-Christof Siegman, Stanford
Synchrotron
Radiation Laboratory
Abstract: Magnetization dynamics have been
excited by laser or magnetic field pulses. In the latter case, the
dynamics depend
critically on the rise time, duration, and amplitude of the initiating
magnetic
field pulse. The relativistic high energy bunches of SLAC have ideal
Gaussian
shape and provide by far the strongest and shortest magnetic field pulses
that
can be produced in a metallic thin film. We demonstrate that magnetic
relaxation phenomena can be studied with the SLAC pulses in actual
magnetic
recording materials as well as in ultrathin epitaxial model films. Special
emphasis will be given to the discussion of ultrafast magnetization
relaxation
claimed in a number of experiments.
Spin-torque for spintronics
Jonathan Sun, IBM Research
T.J.
Watson
Research
Center
A deeper understanding of the basic
physics in
magnetism and magneto-transport is needed for today's magnetic
nanostructures
that are increasingly important for modern electronics. As an example I
will
discuss the discovery and understanding of a spin-angular momentum
transfer
effect in magnetic nanostructures. I will discuss the basic physics
involved,
the recent experimental progress, and the relevance these nderstandings
may
have on emerging magnetic memory technologies in light of its scaling
behavior
in stability against thermally activated reversal in
nanomagnets.
Dissipationless spin current induced by
the
electric field
Andrei Bernevig, Stanford
University
Abstract=Two of the main goals of
spintronics
are the low power logical operation and the manipulation of the spin
degrees of
freedom by the electric field. Recently, it has been theoretically
predicted
that semiconductors with spin-orbit coupling placed under an electric
field
exhibit a dissipationless spin current polarized perpendicular to the
electric
field and the direction of flow (spin Hall effect). In this talk, we shall
review the recent theoretical developments and various proposals to
experimental detect such a spin current.
Transport measurements in a magnetically doped 2D
electron system
John Cumings
Stanford University
Two-dimensional electron
systems
in GaAs semiconductors have proven to be a fruitful area for studying the
basic
physics of electrons confined to nanometer-scale spaces. Using electric
gates
patterned with high-resolution lithography, it is possible to confine
electrons
to small canals and droplets, creating tunable single-state conduction
channels
and artificial atoms. This system is also an obvious area to explore
magnetism
and spin in confined electron systems, however experiments to date have
been
hampered by the lack of good magnetic materials. The 2D GaAs systems are
not
ferromagnetic, and studies of Zeeman effects are disadvantaged by the
relatively low g-factor, |g| < 2. I will present preliminary studies
on a
2D electron system fabricated from a magnetic semiconductor in lieu of the
traditional non-magnetic GaAs. These materials cannot yet be made
ferromagnetic, but nevertheless, interactions with the paramagnetic
dopants
yield an effective g-factor for the electrons that can be over 100. With
such
a large g-factor, the Zeeman splitting can be made to be larger than the
Fermi
energy at modest magnetic fields, producing a completely spin-polarized 2D
system. These materials therefore provide an entirely new paradigm for
studying spin in confined electron systems.
Tunnel spin injectors for semiconductor
spintronics
Xin
Jiang
IBM Almaden Research Center, San
Jose
Spin-based
electronics aims to develop novel sensor, memory and logic devices by
manipulating the spin states of carriers in semiconducting materials.
This
talk will focus on electrical spin injection into semiconductors, which is
a
prerequisite for spintronics and, in particular, on tunnel based spin injectors that are potentially operable
above
room temperature. The magneto-transport properties of two families of
tunnel
spin injectors will be discussed. The first type of spin injector, the
magnetic
tunnel transistor, utilizes spin-filtering effect of hot electrons in
ferromagnetic metals to achieve high spin polarization. The second type,
a
tunnel barrier spin injector, relies on the high tunneling spin
polarization of
a CoFe/MgO structure. The spin polarization of the electron current within
the
semiconductor is detected by measuring the circular polarization of the
electroluminescence (EL) from a quantum well light emitting diode
structure. The
temperature and bias dependence of the EL polarization provides insight
into
the mechanism of spin relaxation within the semiconductor
heterostructure.
Hysteretic electroluminescence in organic
light-emitting
diodes for spin injection
G. Salis, S. Alvarado and R. Allenspach
IBM Research, Zurich Research Laboratory, Säumerstrasse 4,
CH-8803 Rüschlikon, Switzerland
The signature of spin injection into
amorphous
organic layers is studied by measuring the electroluminescence intensity
of
organic light-emitting diodes (OLEDs) with ferromagnetic contacts. In the
organic material, parallel electron and hole spins form non-radiative
triplet
states, reducing the luminescence intensity as compared with antiparallel
electron and hole spins. This effect provides a means to detect the
injection
of spin-polarized charge carriers. OLEDs with an organic-layer thickness
between 50 and 100 nm are fabricated, and contacted by Ni and Co anodes
and permalloy
cathodes. The different coercive fields of the magnetic electrodes allow
the
magnetization of the electrodes to be switched independently by a magnetic
field applied in the plane of the sample. The electroluminescence
intensity is
studied at room temperature as a function of applied magnetic field. We
find a
hysteretic electroluminescence that has a higher intensity for the
antiparallel
magnetic configuration than for the parallel one. By analyzing this effect
as a
function of the applied bias voltage and comparing the results with those
of OLEDs
that have only one magnetic electrode, we show that the hysteretic
electroluminescence is not evidence for spin injection. Instead, an
overall
magnetic-field dependence of the electroluminescence intensity makes the
signal
susceptible for magnetic stray-fields, which mimic the behavior expected
for
injection of spin-polarized charge carriers. From the data, an upper limit
for
the spin polarization of electrons and holes is extracted.
Optical transient-grating detection of spin-motion in
GaAs
Christopher Webber
Lawrence
Berkeley
National
Laboratory
We use an ultrafast, optical pump-probe
method
to create and measure nonequilibrium spin populations in GaAs. Our
coherent,
transient-grating technique allows phase-sensitive detection of spin
propagation on submicron length-scales. Measurement of the magneto-optical
Kerr
effect gives the spin lifetime. We demonstrate measurement of a
spin-diffusion constant
of 90 cm2/s in a quantum well at room temperature, and show
temperature-dependent
results. We discuss the possibilities of measuring submicron drift of spin
populations and of measuring spin-propagation in ferromagnetic
semiconductors.
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