Larysa Tryputen

Polymethyl methacrylate/hydrogen silsesquioxane bilayer resist electron beam lithography process for etching 25 nm wide magnetic wires

A method of patterning magnetic metallic thin films is presented using a bilayer polymethyl methacrylate and hydrogen silsesquioxane electron beam lithography resist mask combined with ion beam etching. The bilayer resist process allows for the combination of a high-resolution resist mask with easy postprocess removal of the mask without damage to the magnetic quality of the film. Co60Fe20B20 and Co/Ni multilayer films were patterned with electron beam lithography at 10–125 keV down to 25 nm wide features with 2 nm average root-mean square edge roughness. Both the in-plane and out-of-plane magnetic anisotropies of the respective film types were preserved after patterning.

360° domain walls: stability, magnetic field and electric current effects

The formation of 360° magnetic domain walls (360DWs) in Co and Ni80Fe20 thin film wires was demonstrated experimentally for different wire widths, by successively injecting two 180° domain walls (180DWs) into the wire. For narrow wires (≤50 nm wide for Co), edge roughness prevented the combination of the 180DWs into a 360DW, and for wide wires (200 nm for Co) the 360DW was unstable and annihilated spontaneously, but over an intermediate range of wire widths, reproducible 360DW formation occurred. The annihilation and dissociation of 360DWs was demonstrated by applying a magnetic field parallel to the wire, showing that annihilation fields were several times higher than dissociation fields in agreement with micromagnetic modeling. The annihilation of a 360DW by current pulsing was demonstrated.

Effects of Edge Taper on Domain Wall Structure and Current-Driven Walker Breakdown in a Ferromagnetic Thin Film Wire

Domain walls in a ferromagnetic thin film wire with rectangular cross section adopt transverse wall (TW) or vortex wall (VW) geometries depending on the magnetic material and the wire width and thickness. However, experimentally wires can have a trapezoidal cross section if they are made by liftoff using an undercut resist profile. Micromagnetic modeling shows that tapering of the wire not only promotes the formation of a TW over a VW, but also increases the critical current value and the domain wall velocity at which Walker breakdown occurs, providing a potential route to higher speed domain wall devices.

Monte Carlo Modeling of Mixed-Anisotropy [Co/Ni] 2 /NiFe Multilayers

The magnetic properties of a thin film consisting of an exchange-coupled [Co/Ni]2/NiFe multilayer have been studied as a function of the NiFe thickness by using Monte Carlo modeling and compared with experimental results of [Co/Ni]4/Co/NiFe multilayers. Both modeling and experiment showed that the NiFe thickness controls the effective anisotropy. The direction of the easy axis is determined by a competition between the perpendicular crystalline anisotropy of the Co/Ni and the shape anisotropy of the multilayer. As the thickness of the NiFe layer increases, the reversal mechanism of the thin film changes from the nucleation of reverse domains to vortex propagation. Therefore, our results reveal the magnetic configurations and the easy axis reorientation of mixed-anisotropy multilayers.