Magnetic nanostructures, referred to as nanomagnets, are the foundation of emerging information storage technologies such as magnetic random access memory (MRAM) devices. Explosive growth in information science and technology sectors demands new storage technologies that are smaller recording bits, densely packed, fast, low-cost, and energy-efficient. Therefore, the magnetic nanostructures used to build magnetic memory need to be small, fast, and uniform across many devices. However, identically engineered nanomagnets' performances deviate from each other due to geometric imperfections, non-uniform material compositions, and manufacturing-related defects. A detailed diagnosis of individual nanomagnets is necessary to unravel the effects of shape, sizes, and manufacturing imperfections on nanomagnets' properties. However, the measurement of nanomagnets' properties is complicated because they are small and buried under many layers. The proposed project aims to measure the properties of individual nanomagnets. The proposed measurement would expose what causes the nanomagnets' performances to deviate from each other. The proposed research will be performed with a collaborator at the University of Nebraska – Lincoln (UNL). The state-of-the-art research tools at the Nebraska Nanoscale Facility will be used to design, fabricate, and measure nanomagnets' properties. The obtained new knowledge will be implemented into the education plans, which empower the future STEM workforce.
The confined geometry of magnetic nanostructures causes spin dynamics to deviate from bulk thin films. In addition to shifting the resonance frequency, multiple spin-wave modes are present. The strong inhomogeneity in the internal magnetic field at the edge allows spin-wave to localize within a few nanometers from the edge. Damages induced during nanopatterning, such as impurities, edge, and interface roughness, can significantly modify spin dynamics. The edges and defects' roles become critical with decreasing size as the spin dynamics deviate among nanomagnets due to a slight deviation in edge roughness and defect densities. The measurement of spin dynamics is complicated because nanomagnets are often buried under nonmagnetic layers, and both conventional metrology tools and routine magnetic measurements are not adequately sensitive. Furthermore, it is difficult to retrieve an individual nanomagnet's covert spin dynamics from the average response of many similar nanomagnets. The proposed research investigates the spectroscopy of spin-wave excitation modes characteristics of individual magnetic nanostructures. The overall goals are to understand the fundamental device physics that controls the dynamic properties of magnetic nanostructures and to understand the source of defects, non-uniformity, and geometrical imperfection among devices and their roles in device performances. The proposed novel method is scanning Nitrogen-Vacancy (NV-) center-based magnetometry combined with real-time locking and tracking of NV- center's magnetic resonance peak. The proposed approach leverage the unique properties of NV- centers whose magnetic resonance frequency shifts due to change in the magnetic field in the vicinity.
This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.
