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The Defense Intelligence Agency's Defense Warning Office issued this Defense Intelligence Reference Document, dated 23 March 2010, as one of a series of advanced technology reports produced in FY 2009 under its Advanced Aerospace Weapon System Applications Program. The report reviews metallic spintronics, including giant magnetoresistance, spin-transfer-torque and antiferromagnetic spintronics, along with their applications. It concludes that spintronic devices could offer radiation-resistant, low-power electronics suited to aerospace use and long space trips.
From the source: Release of 2026-09-18 Incident: 3/23/10, Las Vegas, Nevada. Released with redactions. This document is a Defense Intelligence Reference Document (DIRD), a technical reference format used by the Defense Intelligence Agency (DIA) to capture baseline knowledge on a specific topic for later analytic use. DIRDs are best understood as reference and synthesis products rather than as original research. It is one of 38 DIRDs produced under the Advanced Aerospace Weapon System Applications Program (AAWSAP) between 2009 and 2011. Because AAWSAP’s scope permitted a broad range of supporting topics, not every DIRD in the series directly concerns aerospace systems or future threat assessment. The following summary reflects the DIRD’s scope and framing at the time of writing and should not be read as implying current validation of the concepts discussed. This DIRD surveys metallic spintronics, a branch of electronics that seeks to use both the electric charge and the magnetic spin of electrons to store, detect, and manipulate information, and argues that the field could lead to faster, lower-power, and more radiation-resistant devices than conventional semiconductor electronics. The report focuses on two main effects: giant magnetoresistance (GMR), which allows magnetic states to be read through changes in electrical resistance, and spin-transfer torque (STT), which allows electrical currents to change those magnetic states. The DIRD reviews their underlying physics, the experimental work then available, and possible applications in memory, sensors, oscillators, and logic devices. The document treats metallic spintronics as a promising field while emphasizing that many of its more advanced proposed applications still require substantial further development.
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studies (Reference 30) on sputtered cobalt-copper (Co/Cu) multilayers revealed
magnetoresistances at room temperatures 3 to 4 times larger than those for iron
chromium and 13 times gr eater than those for the permalloy films that were used as
magnetoresistive sensors in magnetic reading heads at that time. The much higher
numbers observed in magnetic multilayers predetermined the fate of GMR in magnetic
recording technology.
The current understanding is that GMR
observed in magnetic multilayers arises
from the dependence of the resistivity
on their internal magnetic configuration
and the role of the external magnetic
field to change this configuration. Figure
2b illustrates GMR in the simple limit
where the electron mean-free-path is
much longer than the layer thicknesses.
The electrical transport properties of the
system are described in terms of the so
called two-current model (Reference
31), based on the suggestion by Mott
(Reference 32) that, at temperatures
lower than the Curie temperature, the
spin -up and spin-down electrons will be
almost independent and carry current in
parallel. Electrons are much more
strongly scattered by a magnetic layer if
they and the local magnetization spin in
opposite rather than the same direction
(R > r). For simplicity, the figure is
drawn with scattering only at interfaces;
however, there is also scattering within
the layers. At zero magnetic field,
where the magnetizations of adjacent
magnetic layers are aligned
antiparallel-for example, because of
exchange coupling between the layers
(Reference 29)-the spin-down
electrons are weakly scattered in layer
R
Bs
J RF ----
0
Magnetic Field
F1 F2 F1 F2
l l ' t - -
t R R t R r t r r
~ ioo}t r r wR R R
Figure 2. (a) Resistance of a magnetic multilayer R
versus magnetic field. {b) Origin of GMR in terms of
spin-dependent electron scattering: F1 aInd F2 are
ferromagnetic layers with a nonmagnetic layer in
between. At zero magnetic field, the magnetizations
in F1 and F2 are aligned antiparallel (center panel)
and can be switched to parallel orientation by an
applied field. (c) The equivalent resistance circuits
corresponding to the three magnetic configurations
shown in (b). See text for details.
Fl but strongly scattered in F2. In contrast, the spin-up electrons are weakly scattered
in layer F2 but strongly scattered in FL As a result, two channels are equivalent,
leading to a total resistance in this "antiferromagnetic" configuration RAF= (R+r)/2 (see
the corresponding resistance circuit in Figure 2c).
When the magnetizations of the two F layers are set into parallel configuration by an
applied magnetic field, the spin-up electrons are weakly scattered in both layers and
form a low-resistivity channel, whereas the spin-down electrons are strongly scattered
in all the layers and form a high - resistivity channel. The reversal of magnetic fii eld just
interchanges the roles of spin-up and spin-down channels. The current's shunting by
the low-resistivity channe'I produces a low total resistance RF= 2Rr/(R+ r) in this
"ferromagnetic" configuration . The size of the GMR is defined as (RAF-RF)/RAF = (R-
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Official release, from the pursue collection. The PDF is mirrored here; the original link is above. 27 pages are in the text index: search them above, or from the library's search.