Ab-initio theory of the magnetic properties of heterogeneous nanostructures

This thesis presents a general formalism for a Density Functional Theory description of the magnetic state of a heterogeneous system, from its paramagnetic high-temperature state to the magnetically ordered ground state. The key ingredient is the identification of localised magnetic moments as emergent electronic degrees of freedom, and the evolution of their orientations under a classical spin Hamiltonian dictated by the underlying electronic structure, computed using Multiple Scattering Theory. The magnetic interactions are contained in the spin-spin correlation function, derived in a linear response approach, and are fully anisotropic, as relativistic effects are accounted for. A range of applications is given. A Mn monolayer on the W(001) is shown to favour a cycloidal spin spiral as ground state, with a well-defined rotational sense due to unidirectional anisotropic interactions. The antiferromagnetism of Mn monolayers on X(111), with X = Pd, Pt, Ag and Au, is analysed, and the triangular Néel state is shown to possess a well-defined chirality pattern. Calculations for bulk zinc{blende MnSb characterise the half-metallic state as being robust against magnetic disorder; this particular polymorph was discovered in epitaxial form by experimentalists at the University of Warwick, and shows promise for spintronics applications. Bulk Co in the hcp and fcc structure reveals the strong feedback between the magnitude of the spin moment and the degree of magnetic order, through the corresponding electronic structure. To conclude, an FeRh film embedded in V is considered. The magnetisation profile corresponding to the imposed antiferromagnetic order is computed self-consistently, and shows the stabilisation of the Fe layers close to the interface with V by those in the interior of the film.EThOS - Electronic Theses Online ServiceFundação para a Ciência e a Tecnologia (FCT) (SFRH/BD/35738/2007)GBUnited Kingdo