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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/ /FOR OFFIElIAk WSE OPtkY (Fa) is "hard" and used to polarize the current, while the spacer (N) is thin enough for the polarized current to get t hrough and excite t he second "free" magnet (Fb) , This Fa/N/Fb trllayer structure is sim ilar to a GMR spin valve . The GMR effect can thus be used to monitor the orientation of Fb relative to Fa - GMR varies linearly with cose, where e is ang le between magnetic moments of Fa and Fb, and a phenomenological description (Reference 46) gives the trilayer resistance R(0) = RF+ (RAF- RF) (1 - cos0)/2. When current flows across Fa/N/Fb, t he current-induced torques act on both Fa and Fb layers (Reference 3, 47). Th is is schematica lly illustrated in Figure 5. This qualitative picture of STT .assumes both Fa and Fb layers are perfect spin filters, so t hat electron spins aligned with t he magnetic moment of, for example, Fa layer are completely transmitted t hrough the layer, while spi ns aligned antiparallel to the layer moment are comp letely reflected. When electron current crosses the Fb/N/Fa trilayer from right to left (Figure Sa), electrons transmitted t hrough Fa will be polarized along Fa. If spin-diffusion length in N is long enough, this spi n- polarized curre nt will reach Fb and exert a torque on Fb in a direction so as to align Fb with Fa. Repeating the argument for Fb, we find that electrons reflected from Fb will be polarized antiparallel to Fb and, hence, in turn exert a torque on Fa trying to alig n Fa antiparallel with Fb. The net result is a pinwheel-type motion with both Fa and Fb rotating in the same direction (clockwise in Figure Sa), as described previously by Slonczewski (Reference 3). When the current crosses the trilayer from left to right, the directions of the torques are reversed (Figure Sb) - the torque on Fa is trying to align Fa parallel with Fb, while the torque on Fb is trying to align Fb antiparallel with Fa . Fb N Fa F N r-¢ V¢- ¢ (b) Electron Current Electron Current Figure 5. Qualitative Picture of STT. (a) For left- going electrons magnetic moments (thin arrows) of both Fa and Fb are rotated clockwi se. (b) For right-going electrons the directions of t he torques (thick arrows) on Fa and Fb are reversed . (Reference 47) The above discussion implies the asymmetry of STT with res pect to current direction as follows. Let's fix t he orientation of the polarizer Fa; in experiments this is usually accomplished by making Fa very t hick (compared wit h Fb) or by pi nn ing its orientation with an adjacent antiferromagnetic layer via the phenomenon of exchange bias. If initially Fb is almost parallel with Fa, t he left-going electrons will stabilize this parallel alignment, and no STT excitation is present. When current bias is reversed , the torque on Fb will try to rotate Fb away from Fa and will result in STT excitation of the system. This asymmetry with respect to current polarity is one of the main features of STT in experiments; see, for insta nce, Figure 5, where STT excitations are present only at negative bias. UNCLASSIFIED/ ,'EAR AEFICIOL !9&i Ql'IL¥ 6
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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.