Control of the motion of domain walls in magnetic nanowires is at the heart of various recently proposed three-dimensional (3D) memory devices. However, fabricating 3D nanostructures is extremely complicated using standard lithography techniques. Here we show that highly pure 3D magnetic nanowires with aspect-ratios of ~100 can be grown using focused electron-beam-induced-deposition. By combining micromanipulation, Kerr magnetometry and magnetic force microscopy, we determine that the magnetisation reversal of the wires occurs via the nucleation and propagation of domain walls. In addition, we demonstrate that the magnetic switching of individual 3D nanostructures can be directly probed by magneto-optical Kerr effect.

We have synthesized a Sr₂CrReO₆ double perovskite sample with the expected high Curie temperature ≈ 600 K, which shows negligible impurity phases and ≈ 15% Cr/Re structural antisite disorder as shown by X-ray and neutron diffraction. High-field magnetization measurements up to 47 T show that the saturation magnetization below room temperature is much higher than the one predicted by simple models that do not take into account the Re spin-orbit coupling. The crucial role of the large Re orbital moment in the physics of Sr₂CrReO₆ and related compound is highlighted.

Using static magnetic fields up to $30\mathrm{T}$ , the authors have measured the high-field magnetization in high-quality samples made from Re-based double perovskites: $A_2\mathrm{Fe}\mathrm{Re}{\mathrm{O}}_6$ ($A_2={\mathrm{Ca}}_2$ , ${\mathrm{Sr}}_2$ , BaSr) and ${\mathrm{Sr}}_2\mathrm{Cr}\mathrm{Re}{\mathrm{O}}_6$ , with Curie temperatures ranging from 360 up to $610\mathrm{K}$ . The results indicate that the saturation magnetization in these compounds is higher than the assumed spin-only ionic values, $3{\mu }_B∕\mathrm{f.u.}$ for $A_2\mathrm{Fe}\mathrm{Re}{\mathrm{O}}_6$ and $1{\mu }_B∕\mathrm{f.u.}$ for ${\mathrm{Sr}}_2\mathrm{Cr}\mathrm{Re}{\mathrm{O}}_6$ , which is explained by the large orbital contribution to the magnetization. Indirectly, these results show that Re-based double perovskites cannot be described as half-metals.

The nature of graphene–metal bonding is crucial for the performance of graphene-based electronic devices. Raman spectroscopy is a powerful technique for probing the electronic behaviour of graphene–metal interfaces. The changes in the Raman spectrum of pristine graphene upon contact with standard metal layers are reported here. In particular, the study is focused on metallization by electron-beam evaporation using chromium or titanium (commonly used as an adhesion layer to improve the bonding of other metals such as gold) and nickel or cobalt (ferromagnetic materials used for spintronics). The results obtained indicate that the main changes in the Raman spectra can be explained in terms of a biaxial strain generated by graphene trying to match the crystalline lattice of the metal. In the case of cobalt, we find that the strong binding of some cobalt atoms to graphene generates a spectrum with a duplication of the characteristic graphene peaks: those corresponding to cobalt physisorbed to graphene and those corresponding to cobalt chemisorbed to graphene, strongly redshifted. Such special behaviour of the graphene–cobalt interface is correlated to the low contact resistance and the enhanced perpendicular magnetic anisotropy of cobalt on graphene.