The unidirectional motion of information carriers such as domain walls in magnetic nanostrips is a key feature for many future spintronic applications based on shift registers. This magnetic ratchet effect has so far been achieved in a limited number of complex nanomagnetic structures, for example, by lithographically engineered pinning sites. Here we report on a simple remagnetization ratchet originated in the asymmetric potential from the designed increasing lengths of magnetostatically coupled ferromagnetic segments in FeCo/Cu cylindrical nanowires. The magnetization reversal in neighboring segments propagates sequentially in steps starting from the shorter segments, irrespective of the applied field direction. This natural and efficient ratchet offers alternatives for the design of three-dimensional advanced storage and logic devices.

The surface and the internal magnetic structure of bamboo-like cylindrical nanowires with tailored diameter modulations have been determined by XMCD/PEEM and MFM.

Control over the magnetization reversal process of nanowires is essential to current advances in modern spintronic media and magnetic data storage. Much effort has been devoted to permalloy nanostrips with rectangular cross section and vanishing crystalline anisotropy. Our aim was to unveil and control the reversal process in FeCoCu nanowires with significant anisotropy and circular cross section with tailored periodical modulations in diameter. Magneto-optical Kerr effect measurements and their angular dependence performed on individual nanowires together with their analysis allow us to conclude that the demagnetization process takes place due to the propagation of a single vortex domain wall which is eventually pinned at given modulations with slightly higher energy barrier. In addition these results create new expectations for further controlling of the propagation of single and multiple domain walls.

We present experimental evidence of transverse magnetic domains, previously observed only in nanostrips, in CoNi cylindrical nanowires with designed crystal symmetry and tailored magnetic anisotropy. The transverse domains are found together with more conventional vortex domains along the same cylindrical nanowire, denoting a bistable system with similar energies. The surface and the inner magnetization distribution in both types of domains are analyzed by photoemission electron microscopy with x-ray magnetic circular dichroism contrast, and hysteresis loop in individual nanowires are measured by magneto-optical Kerr effect. These experimental data are understood and compared with complementary micromagnetic simulations.

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“ Domain wall traps ” have been engineered and well-exploited in nanostrips by creating a geometrical trapping site, e.g. a single notch along a stripe, compared to diameter-modulated (DM) cylindrical magnetic nanowires (NWs) where multi-segmented DM-NWs have been generally studied. Here, we report our systematic study on the magnetization behavior, domain wall structure and its nucleation/propagation in tri-segmented diameter-modulated Ni nanowires, a simple system to investigate the magnetization reversal as function of segment geometry and lay-out order . We find out that the magnetization behavior of single Ni DM-NWs exhibits the significance of positional ordering of thick and thin segments, distinguished by two distinct geometries including: dumbbell-type (type I) and rolling pin-type (type II). Based on experimental and theoretical simulations, it was evidenced that the wide-narrow junctions create trap sites for domain walls where the narrow segment restricts their motion. This type of geometrically engineered nanowires exhibit potential efficiency for future novel spintronic devices in particular when assembled in arrays of DM-NWs as a practical three-dimensional memory device.

Series of high hexagonally ordered compositionally modulated nanowire arrays, with different Cu layer and FeCoCu segment thicknesses and a constant diameter of 35 nm, were fabricated by electroplating from a single electrolytic bath into anodic aluminum oxide membranes. The objective of the study was to determine the influence of ferromagnetic (FM) segment and non-ferromagnetic (NFM) layer thickness on the magnetic properties, particularly coercivity and magnetic interactions. First-order reversal curve (FORC) measurements and simulations were performed to quantify the effect of the inter-/intra-nanowire magnetostatic interactions on the coercivity and interaction field distributions. The FORC coercivity increases for a thick NFM layer and long FM segments due to decoupling of the the FM segments and the increased shape anisotropy, respectively. On the other hand, the interaction field presents a parallel strong reduction for a thick NFM layer and thin FM segments, which is ascribed to a similar NFM/FM thickness ratio and degree of FM segment decoupling along the nanowire.

The electronic structure of crystalline CdTe, CdO, α-TeO2, CdTeO3 and Cd3TeO6 is studied by means of first principles calculations. The band structure, total and partial density of states, and charge densities are presented. For α-TeO2 and CdTeO3, Density Functional Theory within the Local Density Approximation (LDA) correctly describes the insulating character of these compounds. In the first four compounds, LDA underestimates the optical bandgap by roughly 1 eV. Based on this trend, we predict an optical bandgap of 1.7 eV for Cd3TeO6. This material shows an isolated conduction band with a low effective mass, thus explaining its semiconducting character observed recently. In all these oxides, the top valence bands are formed mainly from the O 2p electrons. On the other hand, the binding energy of the Cd 4d band, relative to the valence band maximum, in the ternary compounds is smaller than in CdTe and CdO.