Control of Composition and Phase at the Nanoscale: The Development of AlMn Nanoparticles

University Of Alabama Tuscaloosa, Tuscaloosa AL

Investigators

Abstract

TECHNICAL SUMMARY: This project will discover methods to synthesize AlMn nanoparticles in the tau phase. Bulk tau-AlMn is ferromagnetic (Ms = 950 emu/cc) with a high magnetocrystalline anisotropy (Ku ~ 1 x 107 erg/cc). These particles are expected to have ideal magnetic properties necessary to support the growth in data storage capacity for magnetic tape beyond the year 2020. This technology demands tight compositional and size distributions. From previous work on FePt it has been determined that a two-step nucleation process can be used to control the compositional uniformity. One metal forms the seed from which the other metal atom heterogeneously nucleates. In this project the approach is to nucleate the formation of Mn seed particles, followed by a heterogeneous reduction of Al3+ at the particle surface. The nucleation step will either be a thermal decomposition of an organometallic manganese compound (e.g., Mn2(CO)10) or reduction of Mn2+. Cyclic voltammetry will be used to determine the reduction potentials for the Mn2+ and Al3+ precursors, thereby providing a means of identifying the reducing agents for the nucleation and growth steps. The particles will be prepared in the presence of trioctylphosphine capping ligands to provide a dispersion of particles in an organic solvent. Reaction conditions will be identified that provide control over the particle composition and size distribution. High resolution TEM images will be used to measure the distributions of particle sizes and EDAX on individual particles will provide their compositions. Post synthesis heat treatment in an inert atmosphere will determine conditions for obtaining the chemically ordered, ferromagnetic tauphase with high magnetocrystalline anisotropy. Time-dependent remnant coercivity measurements will provide values of important magnetic properties, i.e, Ms, Hk, Ku, and V. The effect of particle size, composition and chemical ordering on the magnetic properties will be ascertained. NON-TECHNICAL SUMMARY: The world-wide demand for information storage capacity is growing faster than our ability to provide data storage media. Magnetic storage tape is the lowest cost, most reliable and highest volume metric storage density medium for archiving digital data. It is an indispensible component of the overall data storage hierarchy. The Information Storage Industry Consortium (INSIC) has projected that by 2018 current magnetic particles will not support further growth in data storage density. This research project aims at addressing the systematic development of a new class of magnetic nanoparticles that will support further increases in storage density and make tape a viable medium beyond 2018. The particles are a ferromagnetic aluminum-manganese tau phase alloy and this project will discover new chemistry to prepare these particles. The development of these particles will require an essential understanding of compositional, phase and structure stability in multi-component metallic alloys in the nanometer regime. The results will elucidate the intrinsic growth mechanisms of nanoparticles. This will bring to fruition the ability to tailor nanoparticles for applications beyond magnetic storage such as catalysis, hyperthermia cancer treatments, and energy harvesting systems. This project will support a graduate student, who will earn a Ph. D. in Materials Science under the joint direction of D. E. Nikles (chemistry) and G. B. Thompson (metallurgy). The student will have a unique multidisciplinary educational experience at the interface between nanoparticle chemical science and nanoparticle metallurgy. The project will also support a high school student who will spend the summer in doing research as part of a Nanoscience and Engineering High School Internship Program.