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介观铁磁Co80Ni20金属纳米颗粒之间和内部的磁相互作用，嵌入在抗磁性PVC基质中。理解将主要从(i)一种实验技术，即磁后效应测量，pi已经发现它在确定量子磁性能方面是独一无二的，以及（ii）一种理论技术，即Preisach建模，pi在过去已经开创了这一技术。本项目将促进对介观纳米粒子中磁振子的玻色-爱因斯坦凝聚的理解，并尝试测量磁振子的宏观量子纠缠。应用于预测新的高密度记录的寿命，而更高风险的是量子计算。本研究对铁磁性的基础物理和具有重要技术意义的磁性纳米系统都具有重要意义。该研究涉及到一种新观察到的现象，即观察纳米结构中的玻色-爱因斯坦凝聚。在布洛赫T3/2定律中观察到明显的畸变，pi给出了热力学解释，这就需要对布洛赫定律进行扩展。（如前所述，布洛赫定律是铁磁性最基本的定律之一。）扩展涉及到考虑磁振子/磁熵项的可能性，从而导致随温度变化的磁振子化学势（迄今为止在传统推导中省略），进而导致磁振子的玻色凝聚。结果表明，在10-50 K温度范围内，铁磁性纳米颗粒的磁后效应出现了明显的峰值，并且在介观区磁化曲线有轻微的上升。这些都是我们通过实验观察到的。化学势对磁后效应和磁化热依赖性的影响与纳米技术有直接关系。如果成功，我们测量宏观量子纠缠的能力将为量子信息的应用铺平道路。如果我们要充分了解介观体系的磁性，这些问题还需要进一步的研究。非技术：纳米结构中磁振子的玻色-爱因斯坦凝聚的研究本身具有广泛的影响。这个项目的成功完成将对电气工程、物理和化学领域的磁性纳米结构的理解产生广泛而重要的影响。纳米电子工业，特别是磁性介质工业，将直接受益于实验和建模结果。通过选择材料制备、尺寸和组成来控制冷凝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。在我们的样本中测量量子纠缠是高风险的，高回报的。本研究被整合到GWU电气工程博士生的培养中。如果项目成功，pi将申请REU资助，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.