Ferromagnetic Nanowire Metamaterials: Theory and Applications
ABSTRACT An overview of ferromagnetic nanowire (FMNW) metamaterials is presented. First, FMNW metamaterials are placed in the historical context of antique composites and 20th Century artificial dielectrics, and presented as an example of second-generation metamaterials following the microstructured metamaterials developed in the first part of the decade. Next, the fabrication processes of FMNW metamaterials and subsequent planar devices are detailed. It is then shown how the geometrical properties of the FMNW structure, such as the wire diameter and the wire nanodisk thicknesses, determine the dc and RF responses of the material. Upon this basis, the modeling of the metamaterial is presented, using a two-level approach where the microscopic (with respect to the wires) susceptibility is derived by solving the Landau-Lifshitz equation and the macroscopic (metamaterial) permittivity and permeability tensors are obtained by effective medium theory. Next, a review of FMNW microwave devices, such as circulators, isolators, and phase shifters, is provided, and the example of an FMNW dual-band edge-mode isolator is studied. Finally, spintronic effects and applications of FMNW metamaterials, such as dc to RF generators and detectors based on the spin-torque transfer phenomenon, are reviewed.
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ABSTRACT: The electrical resistivity of Fe-Cr-Fe layers with antiferromagnetic interlayer exchange increases when the magnetizations of the Fe layers are aligned antiparallel. The effect is much stronger than the usual anisotropic magnetoresistance and further increases in structures with more than two Fe layers. It can be explained in terms of spin-flip scattering of conduction electrons caused by the antiparallel alignment of the magnetization.Physical review. B, Condensed matter 04/1989; 39(7):4828-4830.
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ABSTRACT: In developing high-sensitivity micro sensors for very weak magnetic field, extremely high permeability magnetic material is essential for the sensing element. In this study, the effect of plating current density in nanocrystalline electrodeposition of permalloy on the crystal grain size and consequently on the soft magnetic properties of the deposited layer of Ni80Fe20/Cu composite wire is investigated. It is found that the coercivity of the deposited Ni80Fe20 increases and the MI effect ratio of the Ni80Fe20/Cu wire decreases with increasing current density in the lower range of current density (0.6–2A/dm2) while the opposite trend is observed as the current density range increases in a higher range (2–8A/dm2). It seems that increasing plating current density has the effect of decreasing the crystal grain size of the plated material, resulting in lower coercivity of the plated material. This effect, due to decreased grain size, is dominating in the higher range of plating current density. However, it also has the effect of increasing residual stresses in the plated material, which is dominating in the lower range of plating current density, resulting in higher coercivity of the plated materials.Journal of Magnetism and Magnetic Materials - J MAGN MAGN MATER. 01/2006; 302(1):113-117.