Conventional electronics rely on the transport of electrons through a circuit to carry information. This comes with ever-present Joule heating as a result of the resistive scattering of electrons. Recent works in the field of spintronics have focused on using magnetic excitations (e.g., spin waves) instead of electrons as a means of information transport without Joule heating. However, realizing long distance information transport using conventional spin waves has proven difficult owing to their diffusive nature and the exponential decay of spin current. Theoretical studies have proposed a new form of magnetization dynamics, referred to as superfluid-like spin transport, as a way to overcome this shortfall. Instead of decaying exponentially with distance, the spin current associated with superfluid-like spin transport decays linearly with distance, potentially allowing for information transport beyond the micron-scale. In this dissertation, I discuss the work that I have done towards realizing this novel phenomenon in a metallic, ferromagnetic system. Results on a reduced damping and reduced magnetic moment Fe-based alloy, micromagnetic simulations that use established domain wall physics to explain superfluid-like spin transport, and an investigation of spin torques found in a current-in-plane spin valve structure with broken in-plane symmetry for excitation of superfluid-like spin transport dynamics are discussed. I conclude by discussing what steps remain before superfluid-like spin transport can be measured in an experimental system as well as the impacts this work could have on the wider spintronics field.
This work was supported in part by National Science Foundation, Grant No. DMR-2003914. / Doctor of Philosophy / All of the electronics devices we use every day depend on tiny, charged particles called electrons moving through a wire. These particles bounce off of and collide with defects within that wire and cause the wire to heat up, dissipating their energy to the surrounding environment. If this could be avoided, the overall power needed to operate our devices could be lowered. To alleviate this problem, scientists take advantage of another property of the electron, its spin (which gives rise to magnetism), to send signals. Since the electron spin can interact with the spin of nearby electrons, information can be transported this way without actually moving the electrons themselves. These magnetic signals can be thought of as the electron spin wiggling a small amount about its axis, somewhat akin to a precessing top. The downside to these magnetic signals is that they decay away very quickly, typically much quicker than electron currents. In this dissertation, I focus on using a different form of magnetic signals, one that can be thought of like a fluid flowing through a pipe, to send information much further than before without significant energy losses. This phenomenon, which I call ``superfluid-like spin transport,'' has the potential to dramatically alter the future development path of next-generation devices. In the first experiment, I discuss the work done to choose a suitable material platform that can host superfluid-like spin transport. Starting with the common magnet iron, we show that by mixing it with the correct non-magnetic material, it is possible to improve the magnetic properties in a way that is beneficial to superfluid-like spin transport. In the next experiment, computer simulations were used to understand how superfluid-like spin transport might behave in a future device. We find that the fluid-like behavior found in this phenomenon can actually be understood by imagining a train of rigid particle-like entities being packed closely together. In the final experiment, I investigate whether a new and potentially simpler device geometry can be used to start the flow of superfluid-like spin transport. It turns out that the mechanism needed to start the flow is surprisingly weak in the material system studied. While this work does not achieve superfluid-like spin transport, it has taken essential steps towards understanding how one might do so in the future using common materials in an easy-to-make manner. I conclude by offering my thoughts of what the next steps would be as well as impacts this work might have on future next-generation energy-efficient devices.
| Identifer | oai:union.ndltd.org:VTETD/oai:vtechworks.lib.vt.edu:10919/110071 |
| Date | 12 May 2022 |
| Creators | Smith, David Acoya |
| Contributors | Physics, Emori, Satoru, Barnes, Edwin Fleming, Nguyen, Vinh, Heremans, Jean Joseph |
| Publisher | Virginia Tech |
| Source Sets | Virginia Tech Theses and Dissertation |
| Language | English |
| Detected Language | English |
| Type | Dissertation |
| Format | ETD, application/pdf, application/pdf |
| Rights | In Copyright, http://rightsstatements.org/vocab/InC/1.0/ |
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