Monica Tanase, Daniel M. Silevitch, Chia-Ling Chien, and Daniel H. Reich

A key feature of electrodeposited nanowires is the ability to vary the composition along the length, allowing for the study of magnetotrasnport properties with current flowing perpendicular to the modulation. Here, we study the magnetic switching behavior of nickel nanowires, where the wires have been mechanically bent. By comparing the properties of these bent wires to similar straight wires, we can look for the effects of interactions between the segments.

We grew 350 nm diameter wires that had a 20 micron central Ni segment and 2 micron Pt endcaps (to give clean electrical contact). After removing the wires from the template, they were spun in a centrifuge, which induces sharp bends in the center of the wire. Lithographic electrical leads were then patterned on top of individual bent wires.

Magnetoresistance curves are shown below for a straight and a 90 degree bent nanowire. The straight wire shows a sharp increase in the resistance at a specific field, known as the "switching field" Hsw. The bent wire shows two independent switching events, corresponding to the two individual segments.

Switching field vs. orientation for a straight wire and two bent wires are shown below. For the straight wire, Hsw(theta) is well-described by the curling model of domain reversal. A similar model can be used to describe the behavior of the bent wires, treating them as two independent straight segments. The solid triangles mark the points where only one switching event is seen in the bent wires. This region is significantly larger than what would be expected from a pure independent-segment view of the bent wires, indicating that there are interactions between the segments that alter the switching fields.

Conclusions

Our ability to address, manipulate and deform single magnetic nanowires allows us new freedom to explore and engineer their properties. The locking of the switching transitions in the bent wires indicate that interactions between the segments are observable. The ability to tune the magnetic response of the nanowires through simple mechanical manipulations suggests that it may be possible to design novel devices that take advantage of the unique properties of electrodeposited nanowires.

Download a preprint: "Magnetotransport Properties of Bent Ferromagnetic Nanowires"