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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 OFFI&IAk W&E 8PtkY In F/N/F tri layers, the relative orientation of the magnetizations of the two Fs is controlled by an externally applied magnetic field B. To achieve well-defined antiparallel and parallel states of the two Flayers, the moment of one Fis often "pinned," via exchange coupling (exchange bias) to an adjacent AFM layer (Reference 88, 89), leaving the moment of the other free to reverse in much smaller B. In a simple AFM/N/AFM sample, just applying a field Bis not expected to be efficient because of the weak effect of external fields on magnetic moments in AFMs. To achieve better control of the AFMs, AFM/N/AFM spin valves can be sandwiched between two F layers to give F/AFM/N/AFM/F, with the two AFM layers differently exchange-coupled to their respective F neighbors. Applying a magnetic field to change the magnetic order of the F layers should then also affect the order of the AFM layers. In addition to AFM/N/AFM and F/AFM/N/AFM/F multilayers, Wei et al. (Reference 87) have studied a variety of structures-F/AFM/N/AFM, AFM/F/N/AFM, F/AFM, and single F and AFM layers-to isolate the MR observations of interest from potential spurious effects . For small applied currents, neither standard current-in-plane (CIP) MR measurements on extended multilayer films nor CPP MR measurements with point contacts showed any MRs for samples of all types. For larger applied currents, small positive CPP MRs (resistance is highest at saturation) were sometimes observed in samples with at least one F layer, while no MR was seen in samples with no Fs. These observations suggest sputtered AFM/N/AFM multilayers do not show AGMR, possibly owing to mostly diffusive transport in such imperfect films. Smal l MRs observed at higher currents in films with F layers may be associated with the suppression at high currents of spin accumulation induced within and around Fs (Reference 90). Further studies on high-quality films are still needed to verify any possible existence of AGMR in such structures. 4 .2 ANTIFERROMAGNETIC STT Stimulated by the theoretical studies in (Reference 84-86), four experimental searches for effects of STT on AFMs have been published so far (Reference 91-94 ), all working with exchange-biased spin-valves (EBSVs) of the form AFM/Fl/N/F2. Here the AFM lies outside the "active" GMR region of the two F layers and serves mainly to "pin" the magnetization of the adjacent F2 layer to a higher reversing (switching) field than that of the "free" Fl layer, leaving the Fl layer free to rotate at a lower field. The pinning is produced either by heating the sample to above the blocking temperature of the AFM, applying a magnetic field, and then cooling to room temperature with the field on or by applying a magnetic field during sample growth. Wei et al. (Reference 91) used a point contact to inject a high de current density j "' 1012 A/m 2 approximately CPP into an EBSV film. Urazhdin and Anthony (Reference 92) sent a de CPP current density j ~ 5 x 1011 A/m 2 into electron-beam-lithography-fabricated nanopillar EBSVs. Tang et al. (Reference 93) sent a de current-in-plane (CIP) current density ~ 1010 A/m 2 into an EBSV film with a metallic AFM. Dai et al. (Reference 94) sent an ac CIP current density j "' 109 A/m 2 into an EBSV film with an insulating AFM. In all of the studies (Reference 91-94), it was found that a sufficiently high bias current can influence the magnetic reversal of the "pinned" Fl layer. As the pinning (ex,change bias) is known to be associated with interfacial AFM moments (Reference 88, 89), this observation can be taken as evidence of effects of the current on the AFM predicted in (Reference 84-86), given that other spurious effects (for example, Joule heating) can be ruled out. UNCLASSIFIED/ ,eFOlil OFFI CI 0L: 11 &: i ODI L:¥ 14
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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.