AAWSAP DIRD, Metallic Spintronics, March 2010

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Metallic Spintroni·cs
1. Introduction
The rapid pace of progress in the computer industry over the past 40
years has been based on the miniaturization of chips and other
computer components. Further miniaturization, however, faces
serious challenges-for example, increasingly high power dissipation.
To continue on pace, the industry must g,o beyond incremental
improvements and embrace radically new technologies. A promising
nanoscale technology known as spintronics (a neologism for "spin­
based electronics"} has emerged. Spintronics refers to the role an
electron spin plays in solid-state physics. Spintronics researchers
aim to develop a revolutionary new class of electronic devices based
on the spin of electrons in addition to the charge. In spintronic
devices, information is carried not by the electron's charge, as in
conventional microchips, but by the electron's intrinsic spin.
Changing the spin of an electron is faster and requires less power
than moving it. Therefore, if a reliable way could be found to control
and manipulate spins, spintronic devices could offer higher data
processing speeds, lower electricity consumption, and many other
advantages over conventional chips, perhaps including the ability to
carry out radically new quantum computations.
Spintronics in ferromagnetic systems is built on a complementary
set of phenomena in which the magnetic configuration of the system
influences its transport properties and vice versa. Giant
magnetoresistance (GMR} (Reference 1, 2} and spin-transfer-torque
(STT} (Reference 3-5} phenomena exemplify such interconnections
in multilayers composed of ferromagnetic (F} and nonmagnetic (N)
layers. The physics and applications of metallic spintronics are
discussed in this report from the perspec:tive of these two
phenomena. GMR, research on which was awarded the Nobel Prize in
Physics in 2007, refers to a large change in resistance of magnetic
multilayers when the relative orientation of magnetic moments in
their constituent ferromagnetic layers is altered by an applied
magnetic field. The inverse effect, STT, in which a large electrical
current density j can perturb the magnetic state of a multilayer, has
also been predicted (Reference 3, 4} and observed in experiments on
current-induced reversal and precession of magnetization
(Reference 5-9} and magnetic domain wall motion (Reference 10,
11}.
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