Spin Dynamics Simulations of Iridium Manganese Alloys

Until the late 1980's, anti-ferromagnets were thought of as theoretically interesting but with no practical application. Since then, this idea has been completely altered, and they are a key element in nearly all magnetic recording devices such as read heads in magnetic hard drives. More recently, the development of antiferromagnetic spintronics has enabled the use of the anti-ferromagnet as the active element and could lead to storage devices with THz speeds, much higher storage densities and a lower power consumption. A current problem in the development of such devices is a lack of understanding of the magnetic properties of antiferromagnets. Atomistic modelling is a powerful tool in understanding these properties as it has the ability to model the materials in atomistic detail on a scale comparable to realistic device sizes. In this thesis, I present an atomistic model of the Iridium Manganese (IrMn) that was created to model the static and dynamic magnetic properties of this complex material. The ground state magnetic structure and thermal stability are calculated including composition effects, disorder effects and finite-size effects. The magnitude and symmetry of the anisotropy in IrMn is calculated, solving a long standing debate between theory and experiment, where the calculations differ orders of magnitude. Finally, an IrMn layer is coupled to a ferromagnet to study the origin of the exchange bias effect, with realistic device sizes, including multiple grains, temperature and interface disorder. The results presented in this thesis determine the properties of IrMn in extraordinary detail, paving the way for a full understanding of this complex and interesting material and its interaction with natural magnets. The work in this thesis has been published in four peer reviewed papers in world leading journals.