Switching fields of magnetic elements with nanometric dimensions have been investigated by Lorentz microscopy using a transmission electron microscope. Acicular elements of Co and Ni80Fe20 were fabricated by electron beam lithography and lift-off techniques. They were 1.6–3.5 μm long, 200 nm wide, and 20–50 nm thick, with flat rectangular ends or triangular pointed ends, and were patterned in linear arrays with center-to-center spacing ranging from 7 μm to 250 nm. Switching fields and reversal behavior of the elements were found to depend strongly on the shape of the ends and, in a closely packed array, on element separation, thereby providing a way of controlling their magnetic properties.

The magnetization distributions of an array of small NiFe elements were studied using Lorentz transmission electron microscopy (LTEM) and magnetic force microscopy (MFM). The dependence of the domain configurations at zero field as a function of the aspect ratio was observed using MFM, and confirms the earlier observations using LTEM. Comparison of the images of similar islands using both techniques elucidate the complementarity between the LTEM and MFM measurements which individually show different facets of the magnetization distributions on soft magnetic thin films.

By combining a finite element tip model and numerical simulations of the tip-sample interaction, it is shown that magnetic force microscopy images of patterned soft elements may be quantitatively compared to experiments, even when performed at low lift heights, while preserving physically realistic tip characteristics. The analysis framework relies on variational principles. Assuming magnetically hard tips, the model is both exact and numerically more accurate than hitherto achieved.

Domains and domain walls in micron and submicron sized magnetic elements can be studied at high resolution using Lorentz microscopy in the transmission electron microscope. In situ magnetizing experiments are possible in which magnetization reversal processes can be viewed directly in the presence of varying magnetic fields. These techniques have been used to investigate small magnetic structures fabricated by electron beam lithography on electron transparent membrane substrates. Patterned elements as small as 200 ×40 nm have been imaged magnetically. Detailed studies have been carried out into the properties of high aspect ratio (acicular) elements of Co and a soft NiFe alloy. It has been found that the coercivity increases as the elements become narrower, down to ultrasmall elements with a width of 40 nm. Element length has no effect so long as the aspect ratio is sufficiently high. Magnetization reversal in acicular elements is known to begin from the ends of the elements, therefore the shape of the ends—flat, elliptical, or pointed—has a significant effect on the coercivity. The magnetic environment of an element is also highly important in determining its properties. A one-dimensional array of closely spaced elements has the same average switching field as an isolated element but the spread in values is greatly increased when the gap between elements is made smaller than the width of an element. Adding rows of elements to make a two-dimensional array also has an effect, even if the rows are spaced further apart than the length of the elements.

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