Magnetotunable left-handed FeSiB ferromagnetic microwires

The magnetotunable left-handed characteristics of Fe(77.5)Si(12.5)B(10) glass-coated ferromagnetic microwires are analyzed in array and single microwire configuration, employing a rectangular waveguide working in X band. While the negative permeability is ascribed to the natural ferromagnetic resonance (NFMR) of the highly and positive magnetostrictive microwire, the negative permittivity features of the medium are attributed to the interaction of the microwires with the metallic rectangular waveguide. The dependence of the NFMR frequency on the applied external magnetic field enables the design of magnetotunable left-handed systems with wide-frequency band.

Model for hyperthermia with arrays of magnetic nanoparticles: spatial and time temperature distributions in tumor

A square array of micron-sized needles containing magnetic nanoparticles has been studied theoretically as potential systems to deliver heat to tumor tissue for the hyperthermia treatment. The spatiotemporal distributions of temperature in a tumor were calculated for different arrays of microneedles. The resulting temperature distributions are found to be more uniform within the tumor target than those caused by other heating systems. Moreover, the temperature profiles could be tuned by a proper choice of the combination of the system parameters: the needle radius, the spatial needles period, as well as the filling fraction and parameters of magnetic nanoparticles.

Temperature and time dependent magnetic phenomena in a nearly stoichiometric Ni(2)MnGa alloy

In this work, the temperature and time dependence of the magnetic properties of a polycrystalline Ni(49.7)Mn(24.1)Ga(26.2) alloy is analysed. The law of approach to magnetic saturation has been employed to estimate the magnetic anisotropy in the three structural phases of the alloy (martensitic, pre-martensitic and austenitic). The temperature dependences of magnetic parameters, such as the magnetic susceptibility and coercive field, are interpreted in terms of the changes in the magnetic anisotropy taking place with the structural transformations. The strong magnetocrystalline anisotropy is confirmed to mainly control the magnetic response of the low temperature martensitic phase. Furthermore, magnetic relaxation studies (magnetic after-effect) have been employed to analyse the main differences between the magnetization processes in the three characteristic structural phases. The time decay of the magnetization displays a distinctive response in the pre-martensitic state. The results (logarithmic time decay of the remanent magnetization and field dependence of the magnetic viscosity) indicate the thermally activated nature of the relaxation process.

Magnetic properties of nickel and cobalt catalysts supported on nanoporous oxides

The aim of this work is to use magnetic measurements as a research tool in the study of possible metal-support interactions in nickel and cobalt nanoporous catalysts. Several physicochemical techniques, namely nitrogen adsorption, X-ray diffraction, temperature-programmed reduction and chemical analysis, were used to analyze the role of the preparation method and the nature of the support on the existence of such metal-support interactions and to relate them with the magnetic response of these nanoporous systems. The catalysts were prepared by incipient wetness impregnation and precipitation-deposition with two commercial oxides, gamma-Al2O3 and SiO2, as supports. The magnetic behavior of the catalysts is drastically affected by the existence of interactions between the metal and the support during the preparation procedure. The samples with weak metal-support interactions have characteristic magnetic behavior of antiferromagnetic metal oxide nanoparticles, while the ones having strong interactions display spin-glass like behavior.