Swift Heavy Ion Irradiation and Thermal Annealing Induced Modification of Structural Topographical and Magnetic Properties in Monolayer and Bilayer Films Based on FeNiMoB and Zinc Ferrite

Abstract

Magnetism and magnetic materials have been playing a lead role in the day to day life of human beings. The human kind owes its gratitude to the lodestone meaning leading stone which lead to the discovery of nations and the onset of modern civilizations. If it was William Gilbert, who first stated that earth was a giant magnet , then it was the turn of Faraday who correlated electricity and magnetism. Magnetic materials find innumerable applications in the form of inductors, read and write heads, motors, storage devices, magnetic resonance imaging and fusion reactors. Now the industry of magnetic materials has almost surpassed the semiconductor industry and this speaks volumes about its importance. Extensive research is being carried out by scientists and engineers to remove obsolescence and invent new devices. Though magnetism can be categorized based on the response of an applied magnetic field in to diamagnetic, paramagnetic, ferromagnetic, ferrimagnetic and antiferromagnetic; it is ferrimagnetic, ferromagnetic and antiferromagnetic materials which have potential applications. The present thesis focusses on these materials, their composite structures and different ways and means to modify their properties for useful applications. newlineIn the past, metals like Fe, Ni and Co were sought after for various applications though iron was in the forefront because of its cost effectiveness and abundance. Later, alloys based on Fe and Ni were increasingly employed. They were used in magnetic heads and in inductors. Ferrites entered the arena and subsequently most of the newer applications were based on ferrites, a ferrimagnetic material, whose composition can be tuned to tailor the magnetic properties. In the late 1950s a new class of magnetic material emerged on the magnetic horizon and they were fondly known as metallic glasses. They are well known for their soft magnetic properties. They were synthesized in the form of melt spun ribbons and are amorphous in nature and they are projected to replace the crystalline counterpartsMetallic glasses are alloys of transition elements and metalloids and have attracted the attention of technologists owing to their superlative soft magnetic properties compared to other conventional crystalline materials. The transition elements like Fe, Co, Ni imparts magnetic properties, while metalloids like B and Si aid in amorphisation and Mo and Nb act as grain growth inhibitors. Nanocrystallinity can be induced in these alloys by thermal annealing and this improvises the soft magnetic properties. The nanocrystalline thin films are highly sought after for read and write heads and sensors. Metallic glass having a composition of Fe40Ni38Mo4B18 exhibits high saturation magnetisation, high Curie temperature and low anisotropy and crystallizes at 4000C. The bulk properties of these alloys are well studied; however studies on thin films are rare in literature. Earlier investigations carried out in this laboratory on thin film forms of these alloys by employing vacuum evaporation yielded films with excellent magnetic properties; however the target and the film composition were at variance. Retaining the composition of the target in the film as well is necessary as this influences the magnetic properties substantially. newline