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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.
UNCLASSIFIED/ /fOft Offl@IAL ~SE 8,.L?f converts a direct current (de) voltage input into an alternating current (ac) voltage output. The frequency of such a precession can be tuned from a few gigahertz (GHz) to > 100 GHz by changing the applied magnetic field and/or de current, effectively resulting in a current-controlled oscillator for use in practical microwave circuits. Since its prediction in 1996, the STT effect has been observed in a number of experiments, including those with mechanical (Reference 5, 9, 40) and lithographic point contacts (Reference 6, 41), manganite junctions (Reference 7), electrochemically grown nanowires (Reference 8), lithographically defined nanopillars (Reference 42, 43), tunnel junctions (Reference 44), and semiconductor structures (Reference 45). These different methods all share one characteristic feature: they make it possible to attain extremely high current densities (>1012 A/m 2 for metallic structures) needed to produce sufficiently large spin-transfer torques (Reference 3, 4 ). This is achieved by forcing the electrical current to flow through a very small constriction. The latter can be a mechanical point contact, a lithographically defined point contact or nanopillar, or a nanowire, as illustrated in Figure 4. I n all cases, the maximum current density jmax = I/A is defined by the current I flowing through the device and the minimum cross sectional area A of the current path. For typical mechanical point contacts, I ~1 mA and A ~100 nm 2 gives jmax ~10 13 A/m 2 . In lithographically defined structures, both I and A are typically larg er, I ~10 mA and A ~10000 nm that gives jmax ~10 A/m2 12 2 , . manganite electrodeposited IIthog raphycalmechanical lithographycal trilayer junctions nanowires pillar devicespoint contacts point contacts e- Figure 4. Device Schematics for STT Experiments. All experiments share one co mmon feature: a small constriction for electrical current-that Is, point contact, junction, nanowire, or nanopillar. Black (grey) Indicates insulator; dark blue indicates mag netic materia l. The basic physical mechanism underlying STT relies on conservation of angular momentum. Consider a pedagogically simple case where a conduction electron crosses an interface between a nonmagnetic metal (N) and a ferromagnet (F). We assume the initial state of the electron's spin S in N is noncollinear to the F's magnetization M. Once into F, S is subject to an exchange torque caused by M that tends to reorient S. Therewith, according to Newton 's Third Law, there should also exist a reaction torque that acts on M - STT torque. Deep into F, S is aligned with M, and the change in angular momentum that occurs from its reorientation has been transferred to M. Hence the phenomenon's name: spin -transfer torque. Of course, the torque applied to M by a single-sp in S is negligibly small owing to S being negligibly small compared with M. For high current density crossing the N/F interface, however, the number of such spins can be very large and the resulting effective S might become comparable to M. This highlights the need for high current densities to observe the STT phenomenon . A typical experiment on current-driven excitation of a ferromagnet usually involves two single-domain thin -film magnets separated by a nonmagnetic spacer. Here one magnet UNCLASSIFIED/ ,CFOA QFFIGIAk W&& 0PtLY 5
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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.