Fabrication and Study of the Structure and Magnetism of Rare-earth Free Nanoclusters

Extensive search for new magnetic materials free of critical rare-earth elements or expensive platinum suitable for technology or energy-applications is one of the main factors driving today's research in magnetism. Development of these new materials is often hindered by conventional bulk-synthesis techniques which result in phase mixtures or poor magnetic properties. This dissertation focusses on this problem by investigating an alternate approach to fabricate nanoclusters of magnetic materials using an inert-gas-condensation cluster-deposition method, and analyzing their potential for magnetic applications. Nanoclusters of hard-magnetic Zr2Co11 were studied which have relatively high magnetocrystalline anisotropy as required for permanent-magnet applications. The Zr2Co11 nanoclusters exhibit high coercivity at room temperature, high magnetization and a high-energy product of 16.6 MGOe. When combined with a soft Fe-Co phase, the energy product rises to 19.5 MGOe. In-situ magnetic alignment of these nanoclusters is also demonstrated, which enhances the remanent magnetization and energy product. Mn5Si3 and Fe5Si3 nanoclusters also were studied and high surface spin polarization was demonstrated for these materials resulting in novel magnetism such as, high magnetization and Curie temperature at the nanoscale compared to bulk. These materials show lattice-matching with semiconductors and high spin-polarization, which suggest further studies of these nanoclusters in the context of spintronics as potential spin-injectors. iii Copyright 2017, Bhaskar Das iv DEDICATION To my parents Aloke Das and Anasuya Das, whose hard work has enabled me to become what I am. They always inspire me to go forward in life in any circumstances and never lost hope in me. To my wife, Moumita, who encourages me to fulfil my dreams by sacrificing a lot of her own. I am very thankful to her to remain patient and drive me to think positively through difficult times. v ACKNOWLEDGEMENTS