Cylindrical nanowires made of soft magnetic materials, in contrast to thin strips, may host domain walls of two distinct topologies. Unexpectedly, we evidence experimentally the dynamic transformation of topology upon wall motion above a field threshold. Micromagnetic simulations highlight the underlying precessional dynamics for one way of the transformation, involving the nucleation of a Bloch-point singularity, however, fail to reproduce the reverse process. This rare discrepancy between micromagnetic simulations and experiments raises fascinating questions in material and computer science.

Nickel nanorods with an average length of 250–420 nm and diameter of 20–26 nm were prepared by pulsed current electrodeposition into porous aluminum oxide templates and dispersed as colloidal probes in water-based viscoelastic matrices. The ferromagnetic single domain nanorods were driven to rotational motion by an oscillating magnetic field. Nanorod rotation was detected using optical transmission of linearly polarized light providing a frequency-dependent complex magneto-optical response function. Quantitative data analysis was derived for the two most basic mechanical equivalents to viscoelastic materials, the Voigt-Kelvin and Maxwell model, respectively, and demonstrated by means of two examples. The transition from a viscous fluid towards a viscoelastic hydrogel with static shear elasticity was monitored by analyzing an isothermal series of magneto-optical measurements of a gelatin sol after temperature quench in terms of the Voigt-Kelvin model. Maxwell-type relaxation was investigated using CTAC/NaSal giant wormlike micellar solution as matrix. The viscosities and shear moduli retrieved from magneto-optical measurements were compared with macroscopic values obtained by conventional shear rheometry. Characteristic features for each model system were found in the rheological properties at both length scales, yet with quantitative differences caused by the small size of the nanorod probe particles.

We establish a method to produce cylindrical magnetic nanowires displaying several segments, with a large versatility in terms of segment diameter and length. It is based on electroplating in alumina templates, the latter being prepared by several steps of anodization, wet etching and atomic layer deposition to produce, widen or shrink pores, respectively. We propose an analytical model to analyze the in-plane and out-of-plane magnetization loops of dense assemblies of multisegmented wires. The model considers inter-wires dipolar fields, end-domain curling and predicts the switching field of individual wires with no adjustable parameter. Its ingredients are crucial to extract reliable parameters from the fitting of loops, such as magnetization or the porosity of the array.