SGER: Magnetic Interactions Between Mesoscopic Ferromagnetic Metallic Nanoparticles: Aftereffect Measurements and Preisach Modeling of Magnons

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TECHNICAL: This transformative project aims at the understanding of the magnetic interactions between and within mesoscopic ferromagnetic Co80Ni20 metallic nanoparticles, embedded in a diamagnetic PVC matrix. The understanding will be primarily sought from (i) an experimental technique, namely magnetic aftereffect measurements, which PIs have found to be unique in its ability to determine quantum magnetic properties, and (ii) a theoretical technique, namely Preisach modeling, which PIs have pioneered in the past. This project will advance the understanding of the Bose-Einstein condensation of magnons in mesoscopic nanoparticles, and attempt to measure the macroscopic quantum entanglement of the magnons. Applications are to the prediction of lifetimes of new high density recording, and more high-risk to quantum computing. Intellectual Merit The research has significance both to the fundamental physics of ferromagnetism as well as to technologically important magnetic nano-systems. The research involves a newly-observed phenomenon, namely the observation of Bose-Einstein condensation in nanostructures. The observation of a visible distortion in the Bloch T3/2 Law for which PIs give a thermodynamic explanation necessitates an extension of the Bloch Law. (The Bloch Law is one of the most fundamental laws of ferromagnetism, as stated earlier.) The extension involves accounting for the possibility of a magnon/magnetic entropy term, leading to a magnon chemical potential (hitherto omitted in the traditional derivation) which varies with temperature, and in turn, to a Bose condensation of the magnons. The result is a visible peaking in the magnetic aftereffect and a subtle upturn of the magnetization curves of ferromagnetic nanoparticles in the mesoscopic regime in the 10-50 K temperature range. These have been observed by us experimentally. The influence of the chemical potential to the magnetic aftereffect and to the thermal dependence of magnetization leads to a direct relationship with nanotechnology. If successful, our ability to measure macroscopic quantum entanglement will pave the way for application to quantum information. These matters require further investigation if we are to have a full understanding of the magnetism of the mesoscopic regime. NON-TECHNICAL: The study of Bose-Einstein condensation of magnons in nanostructures is of broad impact per se. Successful completion of this project will have wide and significant implications in understanding of magnetic nanostructures for electrical engineering, physics, and chemistry. The nanoelectronics industry, particularly the magnetic media industry, will benefit directly from the experiments and modeling results. The control of the condensation through choice of materials preparation, size, and composition will require a deep theoretical understanding of the thermodynamics underlying the magnetic behavior of nanostructures. The measurement of quantum entanglement in our samples is high-risk, high payoff. This research is integrated into the training of doctoral students in Electrical Engineering at GWU. If successful in this project, PIs will apply for a REU grant to add two undergraduate students.