The method of ferromagnetic resonance (FMR) was used to study magnetic properties of thin films of half-metallic ferromagnetic Heusler alloys Co 2 Cr 0.6 Fe 0.4 Al and Co 2 MnSi depending on the film thickness and the presence or absence of a vanadium buffer layer. It is shown that the FMR method is a highly efficient technique for studying nanoscale magnetic properties of thin films, especially for the investigation of their magnetic inhomogeneities and anisotropy. Samples of Co 2 Cr 0.6 Fe 0.4 Al and Co 2 MnSi were prepared by magnetron-sputtering deposition on substrates of single-crystal silicon dioxide (SiO 2 ) with an orientation (100). It has been shown that the magnetic properties of thin Co 2 Cr 0.6 Fe 0.4 Al films strongly depend on both the film thickness (25 or 100 nm) and the presence of an intermediate vanadium layer (50 nm). Well-resolved spin-wave modes were observed in the sample 100 nm thick without a vanadium buffer layer, which made it possible to determine the parameter of spin stiffness D for this ferromagnet. Two series of thin films of Co 2 MnSi have also been studied, which were prepared on a buffer layer of vanadium (42 nm thick): (1) with various thicknesses (4–100 nm) and a fixed annealing temperature (450°C) and (2) with a fixed thickness (80 nm) and various annealing temperatures (425–550°C). It has been shown that in the series of Co 2 MnSi films with a variable thickness (4–100 nm) the greatest value of magnetization is reached for a film with a thickness of 61 nm. The investigations of the other series of films, which were annealed at various temperatures, show that to achieve both a greater magnetization and a better structural homogeneity, annealing at temperatures T ≥ 450°C is required. In addition, low-intensity spin-waves were observed in some samples with thicknesses of 100 and 61 nm, which made it possible to estimate the spin-stiffness parameter D for the Co 2 MnSi Heusler alloy as well.

Spintronics needs half-metallic materials implemented in technologically relevant devices. We prepare Co2MnSi/AlOx/Co7Fe3 junctions showing a tunneling magnetoresistance of 94.6% at 1 mV and 20 K. Their inelastic electron tunneling spectra at 20 K show typical magnon and phonon excitations in the electrode and the barrier and an additional shoulder around −22 mV not observed in Co7Fe3/AlOx/Ni81Fe19 reference junctions. Furthermore, the bias voltage and temperature dependence of the tunneling magnetoresistance is considerably larger than for the reference junctions. The transport properties are discussed with respect to a variety of current contributions associated with the structural and magnetic properties of the Co2MnSi/AlOx interface.

In this paper, we present a complete optimization loop in order to maximize the efficiency of turbine blades. The optimization of the shape of turbine blades is considered within the context of a whole turbine stage. Thus, also stator/rotor interactions are taken into account. An essential part of the optimization loop is providing gradient information in order to increase efficiency. The derivation of the sensitivity equation and its discretization within the framework of the underlying flow solver is the main part of the paper. The performance of the optimzation loop is demonstrated on a complete turbine stage.

Magnetic tunnel junctions with a magnetically soft Heusler-alloy electrode (Co2MnSi/Al+oxidation+in situ annealing/Co7Fe3/Mn83Ir17) and a maximal tunnel magnetoresistance effect of 86% at 10 K/10 mV are investigated with respect to their structural and magnetic properties at the lower barrier interface by electron and x-ray absorption spectroscopy. A plasma-oxidation-induced Mn/Si segregation and oxide formation at the barrier interface is found, which results in a strongly increased area-resistance product of the junctions, because of an enlarged barrier thickness. For Co2MnSi thickness equal to 8 nm or larger, ferromagnetic order of Mn and Co spins at the interface is induced by annealing; simultaneously, atomic ordering at the interface is observed. The influence of the structural and magnetic interface properties on the temperature-dependent transport properties of the junctions is discussed.

We have integrated Co2MnSi as a representative of the full-Heusler compound family as one magnetic electrode into technological relevant magnetic tunnel junctions. The preparation strategy has been chosen so as to sputter Co2MnSi at room temperature onto a V-buffer layer, which assists in (110) texture formation, and to deposit the Al-barrier layer directly thereafter. After plasma oxidizing the Al-barrier layer subsequent annealing leads (1) to the texture formation and (2) to the appropriate atomic ordering within the Co2MnSi and (3) homogenizes the AlOx-barrier. The resulting magnetoresistance of the Co2MnSi containing magnetic tunnel junctions has been determined as a function of temperature. At a bias voltage of 1 mV a magnetoresistance of 94.6% has been realized at 20 K leading to a spin polarization of 65.5%. Furthermore, the microstructural as well as magnetic quality of the Co2MnSi/AlOx-barrier interface has been investigated in detail. Additionally, the problem of antisite formation at the Co2MnSi/AlOx-barrier interface is experimentally addressed by intercalating thin Co layers in between the Heusler layer and the AlOx barrier. (C) 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Large opportunities in magnetolectronic devices are opened by the spin dependent tunnelling resistance, where a strong dependence of the tunnelling current on an external magnetic field can be found. Within a short time, the quality of the junctions increased dramatically. We will briefly address some important basics depending on the material stacking sequence of the underlying thin film system with special regard to the ferromagnetic electrodes. Scaling issues, i.e. the influence of the geometry of small tunnelling junctions especially on the magnetic switching behaviour are considered down to junction sizes below 0.01 mum(2). The last part will give a short overview on applications beyond the use of the tunnelling elements as storage cells in MRAMs. This concerns mainly field programmable logic circuits, where we demonstrate the clocked operation of a programmed AND gate. The second 'unconventional' feature is the use as sensing elements in DNA or protein biochips, where molecules marked magnetically with commercial beads can be detected via the dipole stray field in a highly sensitive and relatively simple way. (C) 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Hard magnetic (HM) thin films have been vertically integrated below giant magnetoresistive (GMR) multilayer sensors in order to shift the operating point of an applicable GMR sensor. The shift in maximum magnetoresistance (MR) peaks was found to be dependent on the thickness of the HM layer. As a result of different bias geometries, which have been tested, current shunting effects mainly reduce the maximum MR amplitudes. A strong microstructural influence on the magnetotransport has been found; meander-shaped microstructures with different stripe widths have been microfabricated in order to investigate the influence of shape anisotropy and stray field geometry on the magnetotransport. As a result, the bias strength, as well as the shape of the HM hysteresis, varies with the underlying microstructured pattern geometries and the angle of applied field. Comparing the major MR loops of meanders with 1.5, 5, and 10 μm structure width of HM/GMR systems, different MR behavior has been found. It was determined that the MR loops are shifted by different field values simultaneously with a change in the MR loop shape. The effect depends on the orientation of applied field with respect to the meander structure, as well as on the structure width. A creeping effect, which demagnetizes the hard layer, has not been observed during sine-shaped switching cycles. The MR response signal of biased multilayers can be understood using numerical calculations.

The discoveries of antiferromagnetic coupling in Fe/Cr multilayers by Grünberg, the Giant MagnetoResistance by Fert and Grünberg and a large tunnelling magnetoresistance at room temperature by Moodera have triggered enormous research on magnetic thin films and magnetoelectronic devices. Large opportunities are especially opened by the spin dependent tunnelling resistance, where a strong dependence of the tunnelling current on an external magnetic field can be found. Within a short time, the quality of these junctions increased dramatically. We will briefly address important basic properties of these junctions depending on the material stacking sequence of the underlying thin film system with special regard to the ferromagnetic electrodes. Next, we discuss scaling issues, i.e. the influence of the geometry of small tunnelling junctions especially on the magnetic switching behaviour down to junction sizes below 0.01 µm2. The last part will give a short overview on applications beyond the use of the tunnelling elements as storage cells in MRAMs. This concerns mainly field programmable logic circuits, where we demonstrate the clocked operation of a programmed AND gate. The second ‘unconventional’ feature is the use as sensing elements in DNA or protein biochips, where molecules marked magnetically with commercial beads can be detected via the dipole stray field in a highly sensitive and relatively simple way.

As a consequence of the growing theoretical predictions of 100% spin-polarized half- and full-Heusler compounds over the past six years, Heusler alloys are among the most promising materials class for future magnetoelectronic and spintronic applications. We have integrated Co2MnSi, as a representative of the full-Heusler compound family, as one magnetic electrode into magnetic tunnel junctions. The preparation strategy has been chosen so as to sputter Co2MnSi at room temperature onto a V-buffer layer, which assists in (110) texture formation, and to deposit the Al-barrier layer directly thereafter. After plasma oxidizing the Al-barrier layer, subsequent annealing leads (1) to the texture formation and (2) to the appropriate atomic ordering within the Co2MnSi, and (3) homogenizes the AlOx barrier. It is shown that the magnetic switching of the ferromagnetic electrodes is well controlled from room temperature down to 10K. The resulting tunnel magnetoresistance-effect amplitude of the Co2MnSi containing magnetic tunnel junctions has been determined as a function of temperature and the spin polarization of the Co2MnSi Heusler compound has been estimated to be 61% at 10K. Thus, the spin polarization of the Co2MnSi layer at 10K exceeds that of conventional transition metals.

Our study presents experimental results on Co2MnSi thin-film preparation and resulting magnetic properties of the Co2MnSi Heusler alloy. The focus of our work is on the important role of the microstructure and the magnetic properties relationships of Co2MnSi thin films prepared using dc magnetron sputtering. We examined the microstructure evolution determined with x-ray diffraction for various substrates, e.g., MgO, SrTiO3, Si and SiO2, at different substrate temperatures. Polycrystalline growth observed at high substrate temperatures is independent of the nature and orientation of the substrate. These films show soft magnetic behavior at a net magnetization of 4.12μB. In contrast, textured growth is obtained at room temperature by introducing a vanadium seed layer. These samples are magnetically harder but possess a magnetization of 0.25μB only. This behavior indicates a two phase film consisting of an amorphous and textured volume. Consequently, sputtering at low argon pressure at high temperature result in very smooth Co2MnSi Heusler films, enabling the Co2MnSi Heusler alloys to serve as electrodes in tunnel magnetoresistance structures.

Summary form only given. The authors have successfully produced Co magnetic nanocrystals organized in patches and chains by adapting the chemical preparation approach of the Alivisatos group (2001). They study the magnetic and transport properties of these nanoclustered systems in order to get insights into the physics of these Co nanocrystals.