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.




Organizers
SSP Parkin (IBM)
GA Sawatzky (UBC)
PCE Stamp (UBC)
SC Zhang (Stanford)