Resumen de Mn-based magnetic films: From monolayers to microislands
The search of alternatives to rare-earth-based permanent magnets has attracted increased attention in the last years. The scarcity of those elements and their location, together with the raise of new technologies, where permanent magnets are a fundamental part, has led to a mismatch in the balance of supply and demand, causing political and social problems. Based on this problem, nowadays many scientists focus their research on finding new rare-earth free permanent magnet compounds and structures with the aim of using them in certain applications, representing, thus, a strong economic impact.
This Thesis provides a systematic study on two Mn-based permanent magnet compounds: MnAl and MnBi. Both of them present excellent magnetic properties and can be potential candidates to substitute rare earth based permanent magnets in certain applications. Both of them have been studied in thin films form. This Thesis has been divided in four parts in the form of Chapters.
Chapter 1 offers a general and theoretical overview about the fundamental aspects covered in this Thesis. From the main reason why MnAl and MnBi compounds have been studied in the form of thin films, followed by a short introduction on the theory of permanent magnets and their fundamental properties, to a summary of the main Mn based permanent magnet compounds.
Chapter 2 explains in detail the experimental techniques used in this Thesis. Both the in situ and the ex situ techniques.
In Chapter 3 the growth of ultra-thin films (few nanometers) of MnAl and MnBi by MBE has been studied. The formation of the ferromagnetic phase of both compounds and their magnetic and structural properties has been analyzed. Two main achievements have been made. First, the in-depth analysis of the surface and interface carried out by in-situ characterization techniques, such as XPS, UPS and LEED. Second, the formation and characterization of the ferromagnetic phase in MnBi ultrathin films, which is quite unusual.
Chapter 4 focuses on the growth of MnBi thin films by sputtering technique. The effect that different sputtering techniques and temperature during deposition exerts on morphological, structural and magnetic properties has been studied. One of the main achievements is the formation of microscopic structures (micromagnets), which, after further studies, could open the path to great advances in microelectromechanical systems (MEMS) and microsurgery applications, among others.
Finally, the Appendix shows a brief study on the oxidation and degradation of the MnBi compound. Variations of morphological, structural and magnetic properties over time have been studied.
