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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//fOlt Offl@IAL ~91! OHL¥ 2. Giant Magnetoresistance 2.1 GMR BASICS This section discusses the phenomenon of giant magnetoresistance (GMR). Excellent reviews of GMR are available elsewhere (Reference 12-22). The focus on physical concepts important for the sections to follow are discussed. GMR in magnetic multilayers refers to a dramatic reduction in the resistance of the multilayers when subjected to an external magnetic field. GMR's size is usually defined as the resistance change in magnetic field relative to its peak value. The effect can be distinguished from the ordinary magnetoresistance (MR) coming from the direct action of the magnetic field on the electron trajectories via the Lorentz force (Reference 23), and from the anisotropic MR, which comes from dependence of the resistivity on the relative orientation of magnetic moment to the current (Reference 24 ). To prepare the magnetic multilayers, where several atomic layers of one (ferromagnetic) material alternate by layers of another (nonmagnetic) material (see Figure 1), a wide variety of deposition methods have been used, such as electrochemical deposition techniques (Reference 25, 26) and various vacuum deposition techniques (Reference 27, 28). The latter shares mainly between two methods using either sputter deposition or molecular beam epitaxy (MBE) systems. Sputter deposition involves knocking off the atoms of the material of interest from a target by particle bombardment, followed by the deposition of high energetic atoms (N2-30 electronvolts [eV]) onto the substrate. A principal advantage of sputter deposition is the ease with which many different materials can be deposited at relatively high deposition rates. In contrast, deposition rates in MBE systems are usually much lower than for sputtering systems, but much lower energies (~0.1 eV) of the evaporated material Current In the Plane Current Perpendicular to the Plane Figure 1. In a Magnetic Multilayer, Several Atomic Layers of Magnetic Material (shown In grey) Alternate With Layers of Nonmagnetic Material (shown in white). GMR occurs in one of two different geometries: (1) when the cu rrent flows in the plane (CIP geometry) of the layers or (2) wh en the current flows perpendicular (CPP geometry) to t he layers. make this technique favorable for growth of highly oriented single-crystalline films. The original observation of GMR (Reference 1) was made on MBE grown iron-chromium (Fe/Cr) mu ltilayers with nearly perfect crystal lin ity. Subsequently, by using sputtered samples that are grown much more rapidly than MBE samples, it was possible not only to reproduce these results but also to observe osci ll ations in the magnetoresistance as the th ickness of the nonmagnetic spacer layers was varied (Reference 29). Subsequent UNCLASSIFIED/ /FOR OFFIGI.t.b W&& &PtblJ 1
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