Single-vortex magnetization distribution and its reversal behaviour in Co–Pt nanotubes

Using template-assisted electrodeposition in partially Au-covered polycarbonate templates, we have successfully deposited equiatomic Co–Pt nanotubes with an external radius R of 100 nm, lengths L of 800–2000 nm and tube-wall thicknesses of 70 nm. By applying different characterization methods – vibrating-sample magnetometry and combined atomic and magnetic force microscopy – we have shown that in as-deposited face-centred cubic Co–Pt nanotubes the magnetization in the remanent state can be described with a vortex-type of closure. Such curling of the magnetization distribution has its origin in the minimization of the demagnetizing field that arises from the surface or volume charges. The demagnetization of single-vortex-type nanotubes proceeds gradually and exhibits only a modest hysteresis. Such nanotubes with a single vortex-type of magnetization distribution possess the unique property of emitting no stray fields in the remanent state, despite their elongated shape, and therefore represent perfect candidates for magnetoresistive random-access-memory devices and for biomedical applications such as targeted drug delivery.