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

技术：这个变革性的项目旨在了解嵌入在抗磁性聚氯乙烯基质中的介观铁磁性Co80Ni20金属纳米颗粒之间和内部的磁性相互作用。理解将主要从(I)实验技术，即磁后效测量，PI发现其在确定量子磁性方面的独特能力，以及(Ii)理论技术，即Preisach模型，由PI在过去开创。该项目将促进对介观纳米粒子中磁子的玻色-爱因斯坦凝聚的理解，并尝试测量磁子的宏观量子纠缠。应用于预测新的高密度记录的寿命，以及对量子计算的更高风险。这项研究对铁磁性的基础物理以及具有重要技术意义的磁性纳米系统都具有重要意义。这项研究涉及一个新观察到的现象，即在纳米结构中观察到玻色-爱因斯坦凝聚。在布洛赫T3/2定律中观察到可见的扭曲，PI给出了热力学解释，因此有必要对布洛赫定律进行推广。(如前所述，布洛赫定律是铁磁性最基本的定律之一。)这一扩展涉及到考虑磁振子/磁熵项的可能性，导致磁振子化学势(在传统推导中被省略)随温度变化，进而导致磁振子的玻色凝聚。结果表明，在10-50K温度范围内，在介观范围内，磁性纳米颗粒的磁后效出现了明显的峰值，磁化曲线出现了微妙的上移。这些都是我们在实验中观察到的。化学势对磁后效和磁化强度的热依赖性的影响导致了与纳米技术的直接关系。如果成功，我们测量宏观量子纠缠的能力将为应用于量子信息铺平道路。如果我们要对介观体系的磁性有一个全面的了解，这些问题需要进一步的研究。非技术性：研究纳米结构中磁子的玻色-爱因斯坦凝聚本身具有广泛的影响。该项目的成功完成将对理解磁性纳米结构在电气工程、物理和化学方面具有广泛而重要的意义。纳米电子行业，特别是磁性媒体行业，将直接从实验和建模结果中受益。通过材料制备、尺寸和组成的选择来控制凝聚，将需要对纳米结构磁性行为背后的热力学有深刻的理论理解。在我们的样品中测量量子纠缠是高风险、高回报的。这项研究被整合到华威大学电气工程博士生的培养中。如果这个项目成功，私人投资机构将申请REU助学金，以增加两名本科生。

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.