Polymagnets: Hierarchical micromagnetic structures in ferromagnetic shape memory alloys
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In multi-ferroic materials such as Ferromagnetic shape memory alloys (FSMAs), the ferromagnetic Weiss domains are superimposed on, and magnetoelastically coupled to the martensite twins. A systematic study of the micromagnetic structure in the zeroth, first, and higher order structural polydomains leads to the concept of ‘polymagnets’. In this concept various micromagnetic structures can be organized into a hierarchy based on their complexity. This is analogous to the concept of structural polydomains, whereby ferroelastic twin domains are organized into a hierarchy according to their complexity. In the same manner that structural domains lower the overall elastic energy of the system, a polymagnet lowers the magnetic energy of the system. This thesis presents a detailed study of the hierarchy of these micromagnetic structures.