Magnetic Behavior of Nanoengineered Lithographic Particles and Arrays in the Single Domain Limit

University Of Washington, Seattle WA

Investigators

Abstract

TECHNICAL SUMMARY: The fundamental goal of this proposal is to address, for the first time, the static and dynamic magnetic behavior of metallic, nanoengineered heterostructures in the single-domain limit and in the size-range of 30-300 nm, that include shape-controlled single layers, tri-layers of synthetic anti-ferromagnets, and heterostructures with exchange-bias and exchange-spring behavior. It will emphasize size-dependent scaling laws, with studies of true nanoscale magnetic exchange phenomena by eliminating longer length-scale effects, collective behavior of large ensemble arrays and free-floating elements with complete degrees of freedom, including rotation. The central focus will be on the fundamental understanding of magnetic reversal behavior, interlayer coupling, exchange interactions, aging and memory effects and relaxation dynamics, all in the single domain limit and in the context of recent theoretical models. This new science will be enabled by high-throughput recently established nanoimprinting routines and by a series of careful and specialized magnetic measurements. Nanoimprinting allows the fabricate of identical, custom-shaped thin-film elements in the lateral size range between 30 and 300 nm over areas as large as several square centimeters---sufficient for macroscopic ensemble measurements. Unlike electron-beam lithography, with patterning times of many hours, nanoimprint lithography can pattern a whole substrate in just a few minutes. Moreover, the proposed synthesis method overcomes two principal limitations of wet-chemistry approaches, i.e. preparing monodisperse particles in this mesoscopic size range and creating heterostructured elements. Finally, the physical/magnetic microstructure at the nanometer length scale of the NLPs will be correlated at all stages with the magnetic properties measured using particle ensembles. NON-TECHNICAL SUMMARY: The properties of materials depend critically on size, especially on the nanometer length scale. Magnetic properties express this behavior most prominently. At the macroscopic scale a magnetic material breaks down into domains to minimize its magnetostatic energy. As the size of the materials is made smaller it is no longer able to sustain multiple domains and becomes a single domain material. At this length scale, it becomes possible to explore fundamental and intrinsic magnetic behavior without the interference of extrinsic characteristics arising from domain walls. It is proposed to use a novel method to synthesize large numbers of such "designer particles" that are homogeneous in size, shape, morphology and magnetic characteristics by a newly developed technique of nanoimprint lithography---a method similar to rubber-stamping but with nanoscale features. This will enable the study of the magnetic response, as well as its time dependence, of sufficiently large number of "particles" to provide statistically significant data and understanding of magnetic behavior on this length scale. This fundamental work also has potential impact on the technologies of information storage, spin electronics, magnetic logic, hard magnets for energy applications and biological sensing. The simultaneous advancement of discovery with teaching, training and learning will be integrated. These activities include developing new lecture modules for an undergraduate course in Nanotechnology and a graduate class on Magnetic Materials. A new interactive exhibit for the annual UW, College of Engineering open house will be developed; is attended by more than 4000 students from local schools. The PI plans to make the extra effort to recruit minority/women students to UW and will specifically work with Spelman College, a historical African-American liberal arts college in Atlanta, which has a joint science/engineering program in place with UW. International collaborations on electron holography with a leading group in Japan are also planned.