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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/ ~fQB OFFICIO! 1155 Ollklf 3.2 STT EXPERIMENTS Section 3.1 introduced the physics of STT in magnetic nanosystems. We have seen that a high-density electrical current can result in torques on magnetic elements of the system. These torques may be used to control and manipulate the system's magnetic state. However, the resulting behavior of the system can differ significantly from case to case, depending on particular conditions of observation. For instance, in modest external magnetic fields, magnetization of a small element can be repeatedly reversed between two stable configurations, while at higher fields, where the reversal is energetically unfavorable, the moment can be set into precession at a very high..... frequency. To understand details of what happens with a magnetic moment S in a particular situation, one can use Newton's Second Law. ..... ..... For S this would be the Landau-Lifshitz-Gilbert equation, where the rate of change of S ..... is set equal to the net torque acting on S: Equation 1: dS _. P J'.) a P dS Jin D (°" P) - - r S x B41 - -IIS x - + I'/ I - .t x .t x .1; dt • S dt e Ben STT Here the first term on the right_Is the torque on a magnetic m~ment S in an effective magnetic field B eff, (including applied, demagnetizing, anisotropy, and other fields), with ;,i the gyromagnetic ratio; the second term is a phenomenological damping term introduced by Gilbert, with a the Gilbert damping parameter; the third term is ......... .... the SST where smalls ands* are unit Damping... vectors along S and the polarizer S *, I is the current, μa is the Bohr magneton, e is the electron charge, and 11 is the spin-polarization factor. The diagram in Figure 6 shows the directions of the three torques from Equation 1. Note that, depending on the polarity of applied current, the STT torque can be either in the same or opposite direction as the damping Figure 6. Torques on a Magnetic Moment in a Magnetic Field and Subject to an Electrical Current torque. In the former case, SIT will effectively result ln an increased damping for any ..... magnitude of the applie~ current and suppress any possible excitations of S from its equilibrium state along B eff. If, however, the STT torque is opposite to the damping, we can distinguish two situations. For currents below a critical current, where STT is... ..... small compared with damping, S spirals toward B eff (red trajectory in Figure 6). For 7 UNCLASSIFIED//liOP OFFICJtL IHii a,111\1
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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.