RESUMEN

The magnetization dynamics of a wound [DyFe(2)(20 Å)/YFe(2)(80 Å)](×40) exchange spring multilayer have been explored in optical pump probe experiments. Ultrafast optical heating was used to modify the magnetic parameters of the multilayer, while the time resolved magneto-optical Kerr effect was used to probe its response. Although the probe signal is dominated by precession and winding of the exchange spring within the soft YFe(2) layer, reorientation of the DyFe(2) hard-layer magnetization is detected on time scales less than 100 ps. Micromagnetic simulations reproduce the main features of the experimental data and indicate a dramatic optically induced reduction of the hard-layer anisotropy. The results establish the feasibility of switching a spring system by means of parametric excitation.

RESUMEN

We report on a metamolecule antenna, based on a fish-scale design but augmented with two split-ring resonators (SRRs) placed within the fish-scale loops. The properties of the antenna resonator, with and without additional SRRs, were examined using finite element method simulations (COMSOL Multiphysics). The simulation findings were subsequently confirmed experimentally, using a vector network analyser coupled to an antenna-loaded coplanar waveguide (CPW). The addition of SRRs to the fish-scale meta-molecule leads to a demonstrably large increase in microwave-absorption. It is shown that the fish-scale/SRR/CPW combination performs as a microwave antenna. Simulations of the antenna gain and far-field emission are presented and discussed.

RESUMEN

Ar(+) ions have been implanted into Laves phase epitaxial thin films of YFe(2) and DyFe(2). Magneto-optical Kerr effect and vibrating sample magnetometry experiments show that the easy and hard axes of magnetization in both materials rotate through an in-plane angle of 90°, whilst the strength of the magnetic anisotropy remains unaltered. This is supported by OOMMF computational modelling. Atomic force microscopy confirms that the film roughness is not affected by implanted ions. X-ray diffraction data show that the lattice parameter expands upon ion implantation, corresponding to a release of strain throughout the entire film following implantation with a critical fluence of 10(17) Ar(+) ions cm(-2). The anisotropy of the films is linked to the strain and from these data it is concluded that the source of anisotropy alters from one where magnetoelastic and magnetocrystalline effects compete to one which is governed solely by magnetocrystalline effects. The ability to locally tune the source of magnetic anisotropy without affecting the film surface and without inducing or eliminating anisotropy could be important in the fabrication of high density magnetic data storage media, spintronic devices and magneto-optical materials.

Asunto(s)

RESUMEN

Nonlinear and switchable metamaterials achieved by artificial structuring on the subwavelength scale have become a central topic in photonics research. Switching with only a few quanta of excitation per metamolecule, metamaterial's elementary building block, is the ultimate goal, achieving which will open new opportunities for energy efficient signal handling and quantum information processing. Recently, arrays of Josephson junction devices have been proposed as a possible solution. However, they require extremely high levels of nanofabrication. Here we introduce a new quantum superconducting metamaterial which exploits the magnetic flux quantization for switching. It does not contain Josephson junctions, making it simple to fabricate and scale into large arrays. The metamaterial was manufactured from a high-temperature superconductor and characterized in the low intensity regime, providing the first observation of the quantum phenomenon of flux exclusion affecting the far-field electromagnetic properties of the metamaterial.

Asunto(s)

RESUMEN

We show that subterahertz transmission of the superconducting metamaterial, an interlinked two-dimensional network of subwavelength resonators connected by a continuous superconducting wire loop, can be dynamically modulated by passing electrical current through it. We have identified the main mechanisms of modulation that correspond to the suppression of the superconductivity in the network by magnetic field and heat dissipation. Using the metamaterial fabricated from thin niobium film, we were able to demonstrate a transmission modulation depth of up to 45% and a bandwidth of at least 100 kHz. The demonstrated approach may be implemented with other superconducting materials at frequencies below the superconducting gap in the THz and subterahertz bands.

RESUMEN

The current status of magnetic moments used in micro-magnetic modelling of the Laves phase rare earth iron REFe(2) inter-metallic compounds is reviewed. In particular, it is argued that both the neutron scattering results and band structure calculations provide little support for the long-held view that the Fe 3d moments are constant across the REFe(2) series, and for the oft-used rule of thumb that the (57)Fe hyperfine field is proportional to the Fe magnetic moment. Nevertheless, it is argued that it is acceptable to employ a simple ferrimagnetic model, in which the free-ion moment is ascribed to the RE ion and a moment of µ(d) = µ(3d) + µ(5d)≈1.5 µ(B) is used for the combined Fe(3d) and Fe-driven RE(5d) moments.

RESUMEN

The magnetic anisotropy parameters in [110] MBE-grown films of REFe(2) (RE, rare earth) compounds are not the same as those in the bulk. This is due to the presence of a shear strain ε(xy), frozen-in during crystal growth. In this paper, magnetic anisotropy parameters for [110] MBE-grown REFe(2) films, that directly involve the shear strain ε(xy), are presented and discussed. In addition to the usual first-order Callen and Callen term [Formula: see text], there are nine second-order terms, six of which involve cross-terms between ε(xy) and the cubic crystal field terms B(4) and B(6). Two of the second-order cross-terms are identified as being important: [Formula: see text] and [Formula: see text]. Of these, the rank-two term [Formula: see text] dominates over a large temperature range. It has the same angular dependence as the first-order term [Formula: see text], but with a more rapid temperature dependence. The correction at T = 0 K for TbFe(2), DyFe(2), HoFe(2), ErFe(2) and TmFe(2), amounts to ∼+9.2%, -13.9%, -11.6%, +14.3%, and 27.1%, respectively. Similar comments are made concerning the rank-four [Formula: see text] term.

RESUMEN

The spontaneous formation of domains of commensurate vortex patterns near rational fractional matching fields of a periodic pinning array has been investigated with high resolution scanning Hall probe microscopy. We show that domain formation is promoted due to the efficient incorporation of mismatched excess vortices and vacancies at the corners of domain walls, which outweighs the energetic cost of creating them. Molecular dynamics simulations with a generic pinning potential reveal that domains are formed only when vortex-vortex interactions are long range.