Influence of internal geometry on magnetization reversal in asymmetric permalloy rings.

We report the magnetization reversal behavior of microstructured Ni80Fe20 rings using magneto-optic indicator film imaging and magnetometry. While the reversal behavior of rings with a symmetric (circular) interior hole agrees with micromagnetic simulations of an onion → vortex → onion transition, we experimentally demonstrate that rings possessing an elliptical hole with an aspect ratio of 2 exhibit complex reversal behavior comprising incoherent domain propagation in the rings. Magneto optic images reveal metastable magnetic configurations that illustrate this incoherent behavior. These results have important implications for understanding the reversal behavior of asymmetric ferromagnetic rings.

Structure and magnetic properties of nanostructured Pd-Fe thin films produced by pulse electrodeposition.

Nanostructured Pd-Fe thin films with varied Fe content were prepared by electrodeposition technique from organic electrolytes on Cu and brass substrates. The structure and the magnetic properties of the films were investigated prior to post-deposition annealing. The structure of the Pd1-xFe(x) thin film with x = 0.14, 0.24, and 0.52 was determined by X-ray diffraction (XRD) and transmission electron microscopy (TEM) as a solid solution of iron in palladium face-centered cubic lattice with the (111) orientation of nanograins relatively to the substrate surface. The films with higher iron concentration, x = 0.74, 0.91, have structure of a solid solution based on the body-centered cubic lattice. The average grain size determined by the scanning electron microscopy (SEM) for the first two alloys is 7-10 nm, and for the latter ones it is about 120 nm. The saturation magnetization of the films has linear dependence on the iron content, but coercivity has non-monotonic dependence on x, i.e., the films with x = 0.68 show highest coercivity. The magnetic anisotropy of the samples is studied by ferromagnetic resonance (FMR) spectroscopy.

Asymmetric domain nucleation and unusual magnetization reversal in ultrathin Co films with perpendicular anisotropy.

We report unexpected phenomena during magnetization reversal in ultrathin Co films and Co/Pt multilayers with perpendicular anisotropy. Using magneto-optical Kerr microscopy and magnetic force microscopy we have observed asymmetrical nucleation centers where the reversal begins for one direction of the field only and is characterized by an acute asymmetry of domain-wall mobility. We have also observed magnetic domains with a continuously varying average magnetization, which can be explained in terms of the coexistence of three magnetic phases: up, down, and striped.