The Iterative Process of Scientific Exploration: Effects of Electrical Current in Nanomagnetic Systems
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In the iterative process of scientific exploration, experimental observations are generalized into hypotheses, leading to predictions subsequently tested in experiments, and so on. In nanoscience and nanotechnology, this process is complicated by the indirect nature of observations, often making it challenging to confirm or disprove scientific predictions. I will illustrate this process with the studies of the effects of electrical currents on nanomagnetic systems. They started with a theoretical prediction, 20 years ago, that spinpolarized current can induce magnetization precession or reversal, which can be utilized in multiple applications from hybrid memory to microwave generation and logic. While the subsequent experiments confirmed this idea, we have found that the predicted precession generally does not occur. I will show how the experimental observations can be explained by the nonlinear dynamical properties inherent to the magnetic systems. Furthermore, I will show a critical reexamination of the theory underlying the current-in-duced phenomena in nanomagnetic systems reveals quantum effects that are conventionally assumed to be negligible at length scales above a few nanometers, but turn out to provide significant contributions to electron transport and magnetization dynamics even in 100 nanometer-scale systems.
- Nano@Tech Lecture Series