Magnetic ordering in 45 nm-diameter multisegmented FeGa/Cu nanowires: Single nanowires and arrays

Magnetic nanowires are ideal candidates for many diverse applications, such as 3D magnetic memory and bio-barcodes, they also allow fundamental studies of magnetic interactions at the nanometer level. Usually their magnetic characterization involves hysteresis loops that represent the weighted averages of each entire array. Here, off-axis electron holography under Lorentz microscopy conditions has been used to observe the magnetization distribution and to determine the saturation magnetization (M_s = 1.26 × 10⁶ A m^-1) of a single 45 nm diameter FeGa(10.5 nm)/Cu(6.5 nm) nanowire. In addition, a row of segmented nanowires still within the alumina growth template was carefully sliced from the array to observe the magnetization distribution resulting from interwire as well as intersegment interactions. Two simultaneous magnetic states were observed in this novel experimental configuration: one is the antiferromagnetic ordering of segments along each wire with ferromagnetic ordering between nanowires and the second is the presence of ferromagnetic vortices along nanowire lengths. Simulations have been performed to verify the presence of both remnant states. These states demonstrate the frustration present in hexagonally packed nanowires and demonstrate the necessity to understand long range magnetic ordering for applications such as 3D magnetic memory.