Spin-dependent transport in antiferro and ferrimagnetic nanostructures

Orateur : Soutenance de Thèse de Pablo MERODIO

The thesis is devoted to theoretical study of spin transfer torque (STT) in antiferromagnet (AF) and ferrimagnetic (FI) based tunnel junct ions, where two AF or FI metal electrodes are separated by a thin nonmagnetic insulating barrier. The behaviour of STT and TMR in these structures is investigated using tight binding technique in the framework of the Keldysh formalism. The spatial distribution of the STT in AF-based MTJs out-of-plane component is found to be staggered, similar to the in-plane component. It is also demonstrated that unlike conventional ferromagnetic-based tunnel junctions, the TMR in AF-based MTJ can increase with applied bias. The additional magnetic complexity inherent to FI materials yields to a richer physics concerning the STT spatial behaviour in FI based tunnel junctions. In particular, the STT spatial distribution within the leads exhibits a striking spin-modulated wave-like behaviour resulting from the interplay between the exchange splittings of the two FI sublattices. Finally, the STT characteristic lengths in AF materials are investigated experimentally. Here, room temperature critical depths and absorption mechanisms of spin currents in IrMn and FeMn are determined by F-resonance and spin pumping. In particular, room temperature critical depths are observed to be originated from di erent absorption mechanisms : dephasing for IrMn and spin ipping for FeMn.

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