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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/ /FOA OFFl&iI.,k Wli& O,.kY r) 2/(R+r) 2 ~ 1. The other definition ti. R/R = (RAF-RF)/RF= (R-r)2/4Rr (unbounded from above) is also in use. Figure 2a shows a magnetoresistance curve typical for magnetic multilayers. The resistance is constant at a minimum value RF above a saturation field Bs (parallel Fs) and rises to a maximum value RAF as the applied magnetic field B approaches zero (antiparallel Fs). GMR occurs in two different geometries (see Figure 1): namely when the current flows in the plane of the layers, or CIP geometry, or when current flows perpendicular to the layers, or CPP geometry. Most of experiments on GMR are carried out in the CIP geometry because measuring the fairly large resistance of a thin film is quite easy (film length is typically orders of magnitude larger than its thickness). Experiments in the CPP geometry are more d'ifficult (Reference 33) and require special techniques for precision measurements of very small resistances ~10-7 - 10-s Q resulting from the "short and wide" geometry of a 1-mm 2 "wide" and 1- ~Lm "long" sample . In order to increase the resistances to easily observable values, microfabrication techniques can be used to reduce the sample's cross-sectional area (Reference 34-36). Finally, a simple and inexpensive point-contact technique (Reference 37) may also be suitable for this purpose. The samples with a reduced cross-sectional area will be of interest for spin transfer-torque experiments presented in Section 3. 2.2 GMR APPLICATIONS GMR is currently used in magnetic field sensors, including those in read heads for computer hard drives, in galvanic isolators, and in nonvolatile random access memory devices. Reading information stored on magnetic har d disk drives in computers was the first large-sca le commercial application of GMR. The information is stored by magnetizing small regions (magnetic domains) of a magnetic recording disk in different directions. The stray magnetic fields from these domains are detected by a GMR sensing element called spin valve. The simplest type of spin valve consists of two ferromagnetic layers separated by a thin, nonmagnetic spacer. The spin-valve resistance is smallest when the magnetizations of the two ferromagnetic layers are para llel and largest when the magnetizations are antiparallel. The antiparallel alignment is achieved by making the two layers respond differently to an external magnetic field; an antiferromagnet in contact with one of the layers is used to effectively "pin" the magnetization in this layer through an effect called "exchange bias." The exceptional responsiveness of spin valves to magnetic fields has enabled very high areal packing densities in hard drives. Other sensor applications using GMR elements include monitoring of a ferrous gear rotation in machinery oper ation (Reference 38) via detection of a changing magnetic flux when a gear tooth passes near the sensor, man itoring of electrical current via detection of the current-induced Oersted magnetic field, and transferring high frequency signals between isolated circuits (Reference 39) via magnetic fields generated by a high-frequency inductor in one circuit and replicated in another circuit by a GMR sensor. UNCLASSIFIED//5O9 AEFICI0L 11 && Q,.L¥ 3
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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.