Revealing Long-Range Magnetic Order in High-Density Nanowire Arrays

High density arrays of ferromagnetic nanowires are critical to realizing next-generation 3D spintronic technologies, such as spin transfer torque-based racetrack memory. Segmented nanowires have emerged as exciting routes towards magnetic memory. To attain anticipated densities, the nanowires must be extremely close to each other. However, the effect of long range ordering interactions remains largely untested, and intersegment/interwire coupling may result in the formation of long-range magnetic correlations.
We used polarization analyzed small angle neutron scattering to probe Fe_xGa_1-x/Cu nanowire arrays, extracting a three-dimensional picture of magnetic ordering. In these wires, competing interactions induce complex, long-range magnetic order including antiferromagnetic interwire stripe patterns, in-plane interwire ferromagnetism, and intrawire fan structures. The magnetic ordering was tunable through either the external field or the segment aspect ratio. We develop a theoretical framework for more accurately treating interwire magnetic interactions in nanowire arrays. This work suggests that arrays of segmented nanowires possess a complex and highly-tunable, long-range magnetic domain structure which must be carefully considered in the design of nanowire-based devices.