Interactions and magnetization reversal of Ni nanowire arrays have been investigated by the first-order reversal curve (FORC) method. Several series of samples with controlled spatial distribution were considered including simple wires of different lengths and diameters (70 and 110 nm) and complex wires with a single modulated diameter along their length. Subtle features of magnetic interactions are revealed through a quantitative analysis of the local interaction field profile distributions obtained from the FORC method. In addition, the FORC analysis indicates that the nanowire systems with a mean diameter of 70 nm appear to be organized in symmetric clusters indicative of a reversal-field memory effect.

Spinel chromite nanoparticles are prospective candidates for a variety of applications from catalysis to depollution. In this work, we used a sol–gel auto-combustion method to synthesize spinel-type MgCr₂O₄ nanoparticles by using fructose (FS), tartaric acid (TA), and hexamethylenetetramine (HMTA) as chelating/fuel agents. The optimal temperature treatment for the formation of impurity-free MgCr₂O₄ nanostructures was found to range from 500 to 750 °C. Fourier transform infrared (FTIR) spectroscopy was used to determine the lattice vibrations of the corresponding chemical bonds from octahedral and tetrahedral positions, and the optical band gap was calculated from UV–VIS spectrophotometry. The stabilization of the spinel phase was proved by X-ray diffraction (XRD) and energy-dispersive X-ray (EDX) analysis. From field-emission scanning electron microscopy (FE-SEM), we found that the size of the constituent particles ranged from 10 to 40 nm. The catalytic activity of the as-prepared MgCr₂O₄ nanocrystals synthesized by using tartaric acid as a chelating/fuel agent was tested on the decomposition of hydrogen peroxide. In particular, we found that the nature of the chelating/fuel agent as well as the energy released during the auto-combustion played an important role on the structural, optical, and catalytic properties of MgCr₂O₄ nanoparticles obtained by this synthetic route.

Systems of magnetic nanowires are considered strong candidates in many technological applications as microwave filters, sensors or for data storage. The main parameter that controls the response of magnetic nanowires assemblies is the aspect ratio of the nanowires. In this paper we modify the aspect ratio by keeping constant the length of nanowires and modifying the nanowires' diameter. Ni nanowires with diameters of 40, 60, 80 nm and constant lengths of 1000 nm and 500 nm were grown with a standard electrodeposition technique in Anodized Aluminum Oxide (AAO) membranes. The samples were studied using vibrating sample magnetometer and X-band ferromagnetic resonance experiments at room temperature. As the nanowire diameter increases, the coercive field increases and also two different types of dependence of resonance field versus aspect ratio were observed. The results are explained taking into account the effects of the magnetostatic interactions and shape anisotropy.

Using a radio-frequency tunnel diode oscillator technique, we measured the temperature dependence of the in-plane London penetration depth $\Delta {\lambda }_{ab}\left(T\right)$ in Fe${}_{1+y}$(Te${}_{1-x}$Se${}_x)$ single crystals, down to temperatures as low as 50 mK. A significant number of samples, with nominal Se concentrations $x=0.36$, 0.40, 0.43, and 0.45, respectively, were studied and in many cases we found that $\Delta {\lambda }_{ab}\left(T\right)$ shows an upturn below 0.7 K, indicative of a paramagnetic-type contribution. After subtracting the magnetic background, the low-temperature behavior of penetration depth is best described by a power law with exponent $n\approx 2$ and with no systematic dependence on the Se concentration. Most importantly, in the limit of $T\to 0$, in some samples we observed a narrow region of linear temperature dependence of penetration depth, suggestive of nodes in the superconducting gap of Fe${}_{1+y}$(Te${}_{1-x}$Se${}_x)$.