Shape critical properties of patterned Permalloy thin films

• Domain reversal observation in Permalloy crosses with and without an external frame.
• Found a linear inverse relationship between coercivity and the µm-scale line width.
• Discovery of an effect on the linear inverse relationship upon adding a frame.
• Found an inverse relationship between the coercivity and the width of the frame.

The effects of shape and edges in magnetic elements with reduced dimensions on the magnetization reversal of cross- and framed cross- shaped Ni79Fe21 (30 nm) films were studied. Remagnetization details in the strips of the patterned structures, which had 3 to 30 µm widths and ~100 µm lengths, were visualized by the magneto-optical indicator film technique. The magneto-optic images revealed three different types of the domain structure formation and evolution in the samples during their magnetization reversal: (i) spin rotation with growth and annihilation of a cross-tie structure in the strips perpendicular to the applied field, (ii) nucleation and fast motion of special boundaries, which consist of a number of coupled vortices located along both edges of the strips parallel to the applied field, and (iii) switching by ripple structure formation with macrodomain nucleation and domain wall motion in the large unpatterned part of the films. It was experimentally revealed that there exists a dependence of the critical field for nucleation and motion of domain walls in the parallel-to-field strips on their width and frame width. In particular, an inverse proportionality between this nucleation field and strip width was found in these strips having micrometer sized widths. Both experimental and simulation results show that, in cases (i) and (ii), the magnetostatic fields, which are formed on the edges of the strips and at their intersections, play a crucial role in the formation of spin inhomogeneities and switching of the samples.