Figure 4. Fabrication and characterization of radially magnetized tubes.

(a) Preparation of radially magnetized tubes via rolling up out-of-plane magnetized multilayer stacks, for example, Co/Pd multilayers. The normal magnetization component is indicated by red and blue. The initial single domain (SD) state transforms into a multidomain (MD) state on tightly rolling up. (b,d) show the remanent states of an out-of-plane magnetized rolled-up nanomembrane with 2 μm diameter (field initially applied along 180°) visualized in MTXM. Dark and bright contrast refer to strong and weak absorption, and a magnetization pointing outside and inside the tube, respectively. Regions with one and two windings are indicated by 1 and 2 W, respectively. The magnetization is reconstructed by analysing the evolution of magnetic contrast with varying projection angle α, for example, between α and α+4°. This operation is illustrated by encircled plus and arrow symbols. Scale bars, 500 nm. (e,f) Schematic illustration of the magnetic domain patterns in tightly wound rolled-up nanomembranes. Large and small domains form along and perpendicularly to the field direction (indicated by arrow), respectively. A multidomain state wrapping around the whole tube as occurring in regions with multiple windings exhibits azimuthally aligned domains.