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Emerging Technologies of Computation

Explore the fundamentals of magnetism and nanomagnets in the context of Magnetic Quantum Dot Cellular Automata (MQCA). Understand concepts such as magnetic domains, their alignment, and the factors influencing magnetostatic energy. This session will delve into the challenges presented by nanomagnets, including their coupling types—ferromagnetic and antiferromagnetic. The critical roles of anisotropy, Zeeman energy, and magnetostriction in magnetic behavior will be discussed. Engage with the current open questions and potential benefits of MQCA in computational technologies.

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Emerging Technologies of Computation

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  1. Emerging Technologies of Computation Montek Singh COMP790-084 Sep 6, 2011

  2. Today: Magnetic Quantum Dot Cellular Automata (MQCA) • Basics of magnetism • Nanomagnets and their coupling • Next class: • Challenges and Benefits • Open questions

  3. Basics of magnetism • Magnetic domains • regions within magnetic material with uniform magnetization… • … separated by “domain walls” • magnetic moments all exactly aligned • responsible for magnetic behavior of “ferromagnetic” materials: iron, nickel, etc. • What causes them? • magneto-static energy is minimized • Other energy terms: • magnetoelastic anisotropy • magnetocrystalline anisotropy • Zeeman energy Magnetic domains

  4. Basics of magnetism • Magnetic domains • more domains reduces magnetostatic energy • but increases wall energy • Single Domain (SD) • 10 to 100nm is a good size

  5. Basics of magnetism • Magnetization • … under externally applied magnetic field (H) • domains change shape and magnetic moments re-orient • walls shift or disappear • even physical shape of material can change somewhat! • called magnetostriction • useful in actuators and sensors • in strong enough field, all domains aligned • minimizes Zeeman energy

  6. Basics of magnetism • Shape-induced magnetic anisotropy • long grains tend to have magnetic moments along the longer dimension • magnetized grain produces internal magnetic field that counters external field • internal field is anisotropic • Magnetization axis can be determined by fabricated shape • gives us two states! • comes in handy for magnetic storage!

  7. Nanomagnets

  8. Nanomagnets • Two types of coupling • ferromagnetically ordered coupling • collinear along the long axes • states line up • antiferromagnetically ordered coupling • side-by-side, in parallel • favors antiparallel: up-down-up-down…

  9. MQCA: majority gate

  10. MQCA: majority gate

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