Periodic Reporting for period 4 - Dynasore (Dynamical magnetic excitations with spin-orbit interaction in realistic nanostructures)
Período documentado: 2020-12-01 hasta 2021-05-31
We propose to go beyond the state of the art by investigating from first-principles the dynamical properties of chiral spin textures in nanostructures from 2-dimensions to 0-dimension with these nanostructures being deposited on different substrates where spin-orbit interaction plays a major role. Understanding their response to external dynamical fields (electric/magnetic) or currents will impact on the burgeoning field of nano-spin-orbitronics. Indeed, to achieve efficient manipulation of nano-sized functional spin textures, it is imperative to exploit and understand their resonant motion, analogous to the role of ferromagnetic resonance in spintronics. A magnetic skyrmion is an example of a spin-swirling texture characterized by a topological number that will be explored. This spin state has huge potential in nanotechnologies thanks to the low spin currents needed to manipulate it.
Based on time-dependent density functional theory and many-body perturbation theory, our innovative scheme will deliver a paradigm shift with respect to existing theoretical methodologies and will provide a fundamental understanding of: (i) the occurrence of chiral spin textures in reduced dimensions, (ii) their dynamical spin-excitation spectra and the coupling of the different excitation degrees of freedom and (iii) their impact on the electronic structure.
We expect that the results collected from this project will contribute to a better understanding on how to realise nano-devices of importance in nanotechnologies and to discover effects that can be useful in storing, manipulating and reading information.
We introduced a new family of chiral magnetic interactions involving multi-spins beyond the usual bilinear Dzyaloashinskii-Moriya interactions (DMI's). The mechanism leading to multi-spin interactions triggers a new Hall effect that we coined the non-collinear Hall effect. We found that topological magnetic textures such as skyrmions carry a topological orbital moment that is not induced by the spin-orbit interaction but instead by the non-collinearity of the spin-texture. We proposed how to measure it with optical means. We also found that skyrmions interact with single atomic defect following a universal pattern dictated by the electronic filling of the electronic states of the defect. This allows us to predict how an atom will interact with skyrmions just by knowing its location in the periodic table. Atom-by-atom manufacturing of multi-atomic defects permits the breeding of their energy profiles. The resulting interaction phenotype is rich and unexpected. Moreover, we demonstrated that atomic defects can be utilised to trigger new highly-efficient modes of spin-mixing magnetoresistance (XMR), introduced previously by our group, enabling the all-electrical detection of non-collinear spin-textures.
We found a new contribution to the orbital magnetic moment, which can be as large as the atomic-like one accessible from standard DFT codes. In the context of spin-excitations, we found that even non-magnetic adatoms can carry excitations of paramagnetic natures, promoting the boring non-magnetic atoms to highly interesting objects for information nanotechnology. We discovered that the zero-bias anomalies known for Co-adatom originate from gaped spin-excitations induced by a finite magnetic anisotropy energy, in contrast to the usual widespread interpretation relating them to Kondo resonances. We also demonstrated that instead of the Kondo resonance, a new many-body state emerge from the interaction of electrons with spin-excitations, which we name spinaron. We furthermore unravelled the dynamical behaviour of Hall effects and have shown that the Hall angles, dynamical spin-orbit torques as well as various magnetoresistance effects get dramatically enhanced in the AC-regime. In nanoscale objects, it is expected that zero-point fluctuations will be important. We evaluated for the first time the zero-point spin-fluctuations and found that they can be as large as the magnetic moments. This has a dramatic impact on magnetic properties such as the magnetic anisotropy energy and the magnetic exchange interactions. We contributed to the establishment of a logical scheme for a four-state memory based on clusters made of three magnetic atoms deposited on a non-magnetic substrate and have shown how atomic manipulation can be utilized to suppress spin-fluctuations by nonlocally enhancing the spatial symmetry of the nanostructure.