Henry Greve

Giant magnetoelectric coefficients in (Fe90Co10)78Si12B10-AlN thin film composites

Thin film magnetoelectric (ME) two–two composites consisting of AlN and amorphous (Fe90Co10)78Si12B10 layers were fabricated by magnetron sputtering on Si (100) substrates. Upon magnetic field annealing they show an extremely high ME coefficient of 737 V/cm Oe at mechanical resonance at 753 Hz and 3.1 V/cm Oe out of resonance at 100 Hz. These are the highest reported ME coefficients in thin film composites ever. Furthermore, the induced magnetic anisotropy by field annealing serves the possibility to obtain a sensor element with a pronounced sensitivity in only one dimension, which allows the realization of a three-dimensional vector field sensor.

Plasmonic properties of Ag nanoclusters in various polymer matrices

Nanocomposite films containing Ag nanoparticles embedded in a polymer matrix of Teflon AF, poly(methyl methacrylate) (PMMA) and Nylon 6 were prepared by vapour phase co-deposition in high vacuum. A large variation of the particle plasmon resonance frequency in the visible region was obtained by increasing the Ag volume fraction from 4-80%. The metal volume fraction was measured by energy dispersive x-ray spectrometry (EDX) and the film thickness was measured by surface profilometry. The position, width and strength of the plasmon resonance depend strongly on the metal filling factor, cluster size and interparticle distance. The microstructure of the nanocomposites (shape, size, size distribution and interparticle separation of metal clusters) was determined by transmission electron microscopy. The effect of the surrounding dielectric medium on the optical properties of nanocomposites was investigated by comparing the Teflon AF/Ag, PMMA/Ag and Nylon/Ag composites.

Low damping resonant magnetoelectric sensors

The signal of magnetic sensors based on resonant cantilevers comprised of elastically coupled piezoelectric and magnetostrictive materials increases as the damping decreases. Here, we demonstrate that air damping which normally is suppressed by evacuation can also be substantially reduced by lowering the resonance frequency. We show that a Si-cantilever structured to include a seismic mass features a resonant magnetoelectric coupling coefficient of 1.8 kV/cmOe at 330 Hz in air.

Nanostructured magnetic Fe–Ni–Co/Teflon multilayers for high-frequency applications in the gigahertz range

Thin multilayer films of sputtered polytetrafluoroethylene (Teflon) and Fe54Ni27Co19 with different layer thicknesses were prepared by vapor-phase tandem deposition. The films show ferromagnetic resonance frequencies from 3.0to4.7GHz and a high-frequency permeability in the range from 100 to 175, while having negligible losses up to 700MHz and a quality factor Q up to 12 at 1GHz. Thus these films could be promising candidates as high-frequency components used, for example, in mobile communication electronics.

Noise Performance of Magnetometers With Resonant Thin-Film Magnetoelectric Sensors

Sensors based on materials with a giant magnetoelectric (ME) effect may be used to measure biomagnetic fields at room temperature. It is necessary to know the noise behavior of the whole detection unit. The noise level of a thin-film ME sensor was measured at room temperature, and suitable types of low-noise amplifiers were investigated. Noise measurements were carried out at room temperature. Results show a sensitivity value of 5.4 pT/ √Hz at a resonance frequency of 330 Hz. Furthermore, the signal-to-noise ratio was investigated in order to improve the sensitivity of the sensor.

Functional Polymer Nanocomposites

While extensive research has been carried out in the field of structural polymer-based nanocomposites much less investigations have been concerned with polymer nanocomposites for functional applications. Among the functional nanomaterials, nanocomposites consisting of metal nanoparticles dispersed in a dielectric matrix are of particular interest due to their novel functional properties offering hosts of new applications. Here, polymers are attractive as matrix, and several approaches have been reported to incorporate metal nanoparticles into polymers. The present review is concerned with the preparation of polymer-based nanocomposites by vapor phase co-and tandem deposition and the resulting functional properties. The techniques involve evaporation and sputtering, respectively, of metallic and organic components and inter alia allow the preparation of composites which contain alloy clusters of well defined composition. Emphasis is placed on soft-magnetic high frequency materials with cut-off frequencies well above 1 GHz and on optical composites with tuned plasmon resonances suitable for ultra thin color filters, Bragg reflectors, and other devices. In addition, antibacterial coatings and sensors for organic vapors are addressed. The latter take advantage of the steep drop of the electrical resistivity at the percolation threshold. First results are also reported on the incorporation of photo-switchable molecules into nanocomposites near the percolation threshold. Moreover, a novel approach to produce magnetic nanorods is presented.

Fully integrable magnetic field sensor based on delta-E effect

A fully integrable magnetic field sensor based on magnetic microelectromechanical systems is presented. The approach yields high application potential since it is compatible with standard micromachining techniques, operates at room-temperature, and provides high bandwidth and vector field capability. The demonstrator presented in this work consists of a tipless commercial atomic force microscope cantilever which is coated with an amorphous thin film layer of (Fe90Co10)78Si12B10. Amplitude and frequency of magnetic fields are measured via the modulation of the oscillation of the microcantilever via the delta-E effect of the FeCoSiB coating.

Self-organization of ultrahigh-density Fe–Ni–Co nanocolumns in Teflon® AF

We demonstrate a single-step and powerful method based on vapor-phase codeposition to fabricate self-organized, ultrahigh-density Fe–Ni–Co nanocolumnar structures in a Teflon® AF matrix. It is shown that at certain deposition parameters the structure of the metal-polymer nanocomposite changes from a cluster to a nanocolumnar morphology. These mostly monodisperse nanocolumns have an average diameter of around 6nm separated by ∼4nm Teflon® AF and were fabricated so far with aspect ratios of up to 30.

Direct measurements of field-induced strain at magnetoelectric interfaces by grazing incidence x-ray diffraction

The magnetic field induced strain at the interface of a magnetoelectric composite, consisting of a ZnO(001) piezoelectric substrate and an amorphous (Fe90Co10)78Si12B10 magnetostrictive layer, was directly determined by grazing incidence X-ray diffraction. Upon applying a magnetic field along the [110] direction, the ZnO single crystal is under tensile strain in [110] direction and compressive strain in [1-10] direction, in agreement with the magnetostriction in the (Fe90Co10)78Si12B10 layer. At room temperature, the saturation strain along [1-10] of about 3 × 10−5 is close to the saturation magnetostriction of the film measured with the cantilever bending technique.

Toroid microinductors with magnetic nanocomposite cores

This paper presents toroid microinductors with magnetic cores consisting of a novel metal-polymer nanocomposite. The investigations aim at fulfilling the demands of small size, high inductance, high operation frequency, and adequate quality factors required for modern mobile communication electronics. The high-frequency behaviour of the toroid inductors was simulated using the Ansoft HFSS field simulator. The simulations show the dependence of the self resonant frequency of the toroid and number of coil turns if the geometry is otherwise fixed. The terminal impedance Z11 is determined from measured and simulated S11 parameters. The comparison of simulated and measured parameters shows reasonable agreement in the high frequency behavior. Inductors were manufactured using thin film deposition techniques, photolithography, electroplating, and etching processes. The magnetic core material was prepared by sputtering.