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This Defense Intelligence Reference Document, dated 23 March 2010 and produced by the Defense Intelligence Agency under its Advanced Aerospace Weapon System Applications (AAWSA) program, is a technical report on metallic spintronics. It explains giant magnetoresistance, spin-transfer torque and antiferromagnetic spintronics, along with their uses in sensors, hard drive read heads and magnetic memory. It concludes that spintronic devices could enable low-power, radiation-resistant electronics suited to aerospace and long space missions.
UNCLASSIFIED/ ,'Fl.HI &FFl&IAI! WOI 8HL'f similar to conventional HDDs; but the racetrack memory would have much higher read/write performance than HOD. 4. Antiferromagnetic Metal Spintronics Recently, MacDonald and coworkers (Reference 84) predicted that effects similar to GMR and STT observed with ferromagnets ought to occur in multilayer systems where the ferromagnetic (F) components are replaced by antiferromagnets (AFM). First, they predicted that the resistance of an AFM spin valve-where two AFM layers are separated by an N spacer-could depend on the relative orientations of the magnetic moments in the two AFM layers (antiferromagnetic GMR = AGMR). Second, they predicted that injecting a sufficiently strong current density into an AFM should affect its magnetic state via current-induced spin torque. These new AFM effects could lead to new all-AFM spintronics where AFMs are used in place of Fs. Replacing F metals with AFM metals in a spintronic device has several advantages. While AGMR of an AFM spin valve was predicted (Reference 84) to be similar in magnitude to GMR in standard F spin valves, the critical current needed to alter the magnetic order in AFMs can be smaller than for Fs, partly because spin torques can act through the entire AFM volume. The estimate of the necessary current density j ~ 109 A/m 2 (Reference 84) was less than the typical j ~ 1011 A/m 2 needed to reverse the magnetic order in F/N/F multilayers (Reference 5-9, 40-43, 48-51). Finally, using AFM metals in spintronic devices in place of F metals would eliminate unwanted effects of shape anisotropy on the magnetic stability of small elements, thus potentially offering better control of the magnetic state in nanoscale systems and easing fabrication requirements. Following the original predictions of MacDonald and coworkers (Reference 84), Xu et al. (Reference 85) calculated the AGMR for a simple AFM/N/AFM/N = FeMn/Cu/FeMn/Cu multilayer, and Gomonay and Loktev (Reference 86) provided additional theoretical evidence that polarized current can destabilize the equilibrium state of an AFM. Note, however, that all calculations to date are for perfect samples and depend on quantum coherence. It is known that disorder can reduce the predicted effects. Experiments are thus crucial to see if any such effects are visible in real samples. 4.1 ANTIFERROMAGNETIC GMR To the author's knowledge 1 the only experimental study searching for AGMR was performed by Wei et al. (Reference 87). They have measured current-in-plane (CIP) and current-perpendicular-to-plane (CPP) magnetoresistances (MR) of magnetic multilayers containing two antiferromagnetic layers separated by a nonmagnetic layer. Such an antiferromagnetic spin valve, AFM/N/AFM, was predicted (Reference 84) to exhibit AGMR similar to GMR seen in ferromagnetic spin valves, F/N/F, containing two ferromagnetic layers separated by a nonmagnetic layer. Note, however, that calculations (Reference 84) assumed ballistic transport in samples with perfect layers and interfaces where AGMR is a consequence of quantum interference effects. Thus, any disorder that produces diffusive scattering and weakens quantum interference will weaken any such AGMR. 13 UNCLASSIFIED/ (502 OEEICIIL lltilii Q:tlkY •
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Report, from the dia 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.