Investigations in Nanotechnology: Tailoring of Magnetic Nanomaterials for Electromagnetic Wave Absorption

In recent years, there has been a growing interest in magnetic nanomaterials used as microwave-absorbing materials due to military and civil applications such as stealth technology and electromagnetic interference. They are used in portable electronic devices such as smart phones and mobile PCs to protect humans from exposure to electromagnetic pollution, which could increase the risk of cancer or other neural illnesses. In defense applications, the surface of ships, submarines, and aircrafts are coated with electromagnetic absorbing materials to reduce the radar cross section (RCS) and increase stealth capabilities. Magnetic materials have long been used as radar absorbers on aircrafts, e.g., in the form of iron ball paint. The absorber is usually applied by painting the metal surface with mixtures of carbonyl iron and polymer which generates magnetic iron or ferrite particles in situ by decomposition and/or oxidation of iron carbonyl. While this approach has been demonstrated to be successful in reduction of the RCS, it can be expected that the poorly defined synthetic approach produces inhomogeneous layers of magnetic materials with a wide distribution of particle sizes and may also generate magnetic particles containing impurities. This lack of control over material structure makes it challenging to systematically study and improve magnetic materials for electromagnetic wave absorption. This research explores the application of magnetic nanomaterials for electromagnetic wave absorption. We present organic solution synthesis routes towards preparation of a wide range of magnetic nanoparticles, including soft and hard magnetic materials. We have been able to manipulate the synthetic conditions to tune the particle size, shape, and composition to tailor the magnetic properties in terms of coercivity (Hc) and magnetization (M0). We have evaluated the dependence of the permittivity (ε) and permeability (μ) of the nanoparticle assemblies on these parameters, based on which we have further derived the correlation between the electromagnetic wave absorption characteristics and the nanoscale architectures of the materials. Our research will substantially advance the fundamental understanding of the electromagnetic wave absorption behavior of magnetic nanomaterials. The materials and technology developed in this research will also have great applications in both civilian and defense industries