Eszter Simon

Giant magnetoresistance in electrodeposited Co-Cu/Cu multilayers: Origin of the absence of oscillatory behavior

A detailed study of the evolution of the magnetoresistance was performed on electrodeposited Co/Cu multilayers with Cu-layer thicknesses ranging from 0.5 to 4.5 nm. For thin Cu layers up to 1.5 nm, anisotropic magnetoresistance AMR was observed, whereas multilayers with thicker Cu layers exhibited clear giant magnetoresistance GMR behavior. The GMR magnitude increased up to about 3.5–4 nm Cu-layer thickness and slightly decreased afterward. According to magnetic measurements, all samples exhibited ferromagnetic FM behavior. The relative remanence turned out to be about 0.75 for both AMR- and GMR-type multilayers. This clearly indicates the absence of an antiferromagnetic AF coupling between adjacent magnetic layers for Cu layers even above 1.5 nm where the GMR effect occurs. The AMR behavior at low spacer thicknesses indicates the presence of strong FM coupling due to, e.g., pinholes in the spacer and/or areas of the Cu layer where the layer thickness is very small. With increasing spacer thickness, the pinhole density reduces and/or the layer thickness uniformity improves, which both lead to a weakening of the FM coupling. This improvement in multilayer structure quality results in a better separation of magnetic layers and the weaker coupling or complete absence of interlayer coupling enables a more random magnetization orientation of adjacent layers, all this leading to an increase in the GMR. Coercive field and zero-field resistivity measurements as well as the results of a structural study reported earlier on the same multilayers provide independent evidence for the microstructural features established here. A critical analysis of former results on electrodeposited Co/Cu multilayers suggests the absence of an oscillating GMR in these systems. It is pointed out that the large GMR reported previously on such Co/Cu multilayers at Cu-layer thicknesses of around 1 nm can be attributed to the presence of a fairly large superparamagnetic SPM fraction rather than being due to a strong AF coupling. In the absence of SPM regions as in the present study, AMR only occurs at low spacer thicknesses due to the dominating FM coupling.

Formation of magnetic skyrmions with tunable properties in PdFe bilayer deposited on Ir(111)

We perform an extensive study of the spin-configurations in a PdFe bilayer on Ir(111) in terms of ab initio and spin-model calculations. We use the spin-cluster expansion technique to obtain spin model parameters, and solve the Landau-Lifshitz-Gilbert equations at zero temperature. In particular, we focus on effects of layer relaxations and the evolution of the magnetic ground state in an external magnetic field. In the absence of a magnetic field, we find a spin-spiral ground state; while applying an external magnetic field, skyrmions are generated in the system. Based on energy calculations of frozen spin configurations with varying magnetic field we obtain excellent agreement for the phase boundaries with available experiments. We find that the wavelength of spin-spirals and the diameter of skyrmions decrease with increasing inward Fe layer relaxation, which is correlated with the increasing ratio of the nearest-neighbor Dzyaloshinskii-Moriya interaction and the isotropic exchange coupling,

Higher-order contributions to the Rashba-Bychkov effect with application to the Bi/Ag(111) surface alloy

D/J

Formation and stability of metastable skyrmionic spin structures with various topologies in an ultrathin film

. Our results also indicate that the applied field needed to stabilize the skyrmion lattice increases when the diameter of individual skyrmions decreases. Based on our observations, we suggest that the formation of the skyrmion lattice can be tuned by small structural modification of the thin film.

Exchange interaction between magnetic adatoms on surfaces of noble metals

In order to explain the anisotropic Rashba-Bychkov effect observed in several metallic-surface-state systems, we use k⋅p perturbation theory with a simple group-theoretical analysis and construct effective Rashba Hamiltonians for different point groups up to third order in the wave number. We perform relativistic ab initio calculations for the (3√×3√)R30∘ Bi/Ag(111) surface alloy, and from the calculated splitting of the band dispersion we find evidence of the predicted third-order terms. Furthermore, we derive expressions for the corresponding third-order Rashba parameters to provide a simple explanation of the qualitative difference concerning the Rashba-Bychkov splitting of the surface states at Au(111) and Bi/Ag(111).

Complex magnetic phase diagram and skyrmion lifetime in an ultrathin film from atomistic simulations

We observe metastable localized spin configurations with topological charges ranging from

Tensile strain-induced softening of iron at high temperature

Q=-3

Spin-correlations and magnetic structure in an Fe monolayer on 5d transition metal surfaces

to

Magnetism of Gadolinium: A First-Principles Perspective

Q=2

Spin-polarized scanning tunneling microscopy characteristics of skyrmionic spin structures exhibiting various topologies

in a (Pt