The fabrication and magnetic properties of acicular magnetic nano-elements

Two different lithographic techniques have been developed for fabricating magnetic nano-elements on ultra-thin electron-transparent substrates thereby allowing transmission electron microscopy to be used to investigate their properties. Here we describe studies of elements of micropolycrystalline Permalloy and cobalt whose thicknesses lie in the range 20-30 nm. Bright field images show that a high degree of edge acuity is attained and elements with lateral dimensions ≈25 nm have been produced. Lorentz microscopy has provided unique insight into the detailed magnetisation reversal mechanisms in acicular elements with widths in the range 100-300 nm. In cobalt elements a single domain occupies most of the volume with complex domain structures existing very close to the ends; switching fields increase markedly with decreasing element width but are substantially independent of element length. The reversal mechanism is found to involve the propagation of a small “reversing” domain structure along the element length. In Permalloy, extensive domain structures are observed in all but the narrowest elements in the remanent state. The response to applied fields is described