Magnetic nano-materials have recently attracted much attention since they may have potentially many new exciting applications in a wide range of areas. The research described in this thesis has particularly focused on design, synthesis, assembling, testing and characterisation of some novel magnetic nano-materials for potential applications. Thus, a number of new magnetic nanoparticles, in particular core-shell metal, metal oxide or alloy particles encapsulated in ultra-thin porous materials including FeOx, FePt, and Fe3Pt in C, Si02 and Ti02 coatings have been prepared using various bottom-up nanochemistry synthetic methods including micro-emulsion, controlled decomposition, polyol reduction process, hydrothermal and slow evaporation techniques. Also, in this thesis, a number of chemical treatments for the surface engineering of the magnetic particles are discussed. It is important to stress that this thesis describes some first exploratory research on the uses of magnetic nanoparticles as magnetic separable nano-carriers for carrying solvent droplets, bio-molecules and catalytically active species (oxidation) for applications. The studies of two dimensional arrays of coated magnetic nanoparticles as ultra high density surfaces for magnetic memory storage and three dimensional arrays as colloid supercrystals for protein separation, etc are also described in this thesis. The thesis is divided into seven chapters. The first chapter reviews the latest literature in the area of magnetic nano-materials. The second chapter describes the uses of these nanomaterials to assist partition coefficient and protein binding constant measurements in collaboration with my sponsor, AstraZeneca. The third, fourth and fifth chapters reveal the design, synthesis and the architecture for one, two and three dimensional assembled magnetic nano-materials for applications. The sixth chapter describes analytical methodologies and instruments used for the characterisation of these particles. The final chapter summarises the main contributions from my research during the PhD period.