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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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similar to conventional HDDs; but the racetrack memory would have much higher
read/write performance than HDD.
4 . Antiferromagnetic Metal Spintronics
Recently, MacDonald and coworkers (Reference 84) predicted that effects similar to
GMR and STT observed with ferromagnets ought to occur in multilayer systems where
the ferromagnetic (F) components are replaced by antiferromagnets (AFM). First, they
predicted that the resistance of an AFM spin valve- where two AFM layers are
separated by an N spacer- could depend on the relative orientations of the magnetic
moments in the two AFM layers (antiferromagnetic GMR = AGMR). Second, they
predicted that injecting a sufficiently strong current density into an AFM should affect
its magnetic state via current-induced spin torque. These new AFM effects could lead to
new all-AFM spintronics where AFMs are used in place of Fs .
Replacing F metals with AFM metals in a spintronic device has several advantages.
While AGMR of an AFM spin valve was predicted (Reference 84) to be sim ilar in
magnitude to GMR in standard F spin valves, the critical current needed to alter the
magnetic order in AFMs can be smaller than for Fs, partly because spin torques can act
through the entire AFM volume. The estimate of the necessary current density j 109N
A/m 2 (Reference 84) was less than the typical j "' 10 11 A/m 2 needed to reverse the
magnetic order in F/N/F multilayers (Reference 5-9, 40 -43, 48 -51). Finally, using AFM
metals in spintronic devices in place of F metals would eliminate unwanted effects of
shape anisotropy on the magnetic stability of small elements, thus potentially offering
better control of the magnetic state in nanoscale systems and easing fabrication
requirements.
Following the original predictions of MacDonald and coworkers (Reference 84), Xu et al.
(Reference 85) calculated the AGMR for a simple AFIM/N/AFM/N = FeMn/Cu/FeMn/Cu
multilayer, and Gomonay and Loktev (Reference 86) provided additional theoretical
evidence that polarized current can destabilize the equilibrium state of an AFM. Note,
however, that all calculations to date are for perfect samples and depend on quantum
coherence. It is known that disorder can reduce the predicted effects. Experiments are
thus crucial to see if any such effects are visible in real samples .
4 . 1 ANTIFERROMAGNETIC GMR
To the author's knowledge, the only experimental study searching for AGMR was
performed by Wei et al. (Reference 87). They have measured current-in-plane {CIP)
and current- perpendicular-to-plane (CPP) magnetoresistances (MR) of magnet1ic
multilayers containing two antiferromagnetic layers separated by a nonmagnetic layer.
Such an antiferromagnetic spin valve, AFM/N/AFM, was predicted (Reference 84) to
exhibit AGMR similar to GMR seen in ferromagnetic spin valves, F/N/F, containii ng two
ferromagnetic layers separated by a nonmagnetic layer. Note, however, that
calculations (Reference 84) assumed ballistic transport in samples with perfect layers
and interfaces where AGMR is a consequence of quantum interference effects. Thus,
any disorder that produces diffusive scattering and weakens quantum interference will
weaken any such AGMR .
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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.