The giant magnetoresistance (GMR) effect is a very basic phenomenon that occurs in magnetic materials ranging from nanoparticles over multilayered thin films to permanent magnets. In this contribution, we first focus on the links between effect characteristic and underlying microstructure. Thereafter, we discuss design criteria for GMR-sensor applications covering automotive, biosensors as well as nanoparticular sensors.

We present transport measurements with magnetoresistance effect amplitudes of up to 260% at room temperature obtained in granular systems consisting of Co nanoparticles embedded in conductive gels as a non-magnetic matrix. In order to gain a better understanding of the transport mechanism in gel during measurement, the granular system was simultaneously monitored by optical microscopy. Gel-like matrices with different conductivities and viscosities were tested and will allow us to realize a highly sensitive granular giant magnetoresistance sensor without the need for lithographic techniques.

In recent years progress has been achieved in the theory of propagating particles that experience scattering due to interactions with magnetic turbulence. Modern theories for transport are nonlinear as opposed to the traditional quasilinear approach. However, nonlinear theories are based on certain assumptions such as approximations of higher-order correlations. Recently it has been demonstrated that very simple approaches, such as the replacement of fourthorder correlations by a product of two second-order correlations, are often not appropriate. In this paper fourth-order correlations are studied analytically by solving the Fokker-Planck equation of particle transport. Special cases are considered for which an exact analytical treatment is possible. Thereafter, the general case is explored using approximations. A unified theory is derived for compound diffusion, the field line random walk limit, and Markovian diffusion of energetic particles.

The formation of magnetic bead or nanoparticle superstructures due to magnetic dipole dipole interactions can be used as configurable matter in order to realize low-cost magnetoresistive sensors with very high GMR-effect amplitudes. Experimentally, this can be realized by immersing magnetic beads or nanoparticles in conductive liquid gels and rearranging them by applying suitable external magnetic fields. After gelatinization of the gel matrix the bead or nanoparticle positions are fixed and the resulting system can be used as a magnetoresistive sensor. In order to optimize such sensor structures we have developed a simulation tool chain that allows us not only to study the structuring process in the liquid state but also to rigorously calculate the magnetoresistive characteristic curves for arbitrary nanoparticle arrangements. As an application, we discuss the role of magnetoresistive sensors in finding answers to molecular recognition.

Smart windows are an important technology in terms of energy saving potential in the building sector due to their ability to control visible light and thermal radiation. The essential component of this type of window glazing is an electrochromic thin film. In addition to the widely established tungsten oxide as the optically active material, in particular the counter electrode offers significant potential for improving the overall device performance. In this study, tantalum vanadium oxide films are prepared by reactive radio-frequency sputtering on fluorine-doped tin oxide substrates and optimized in terms of their spectro-electrochemical properties as ion storage layer. We show that an oxide-based tantalum-vanadium alloy is a promising approach to address the open challenges of pure vanadium pentoxide. The coatings exhibit color neutrality in combination with a high transmittance of up to 80% in the as-prepared state and suitable optical transmittance switching. Additionally, we find both a sufficient stability upon cycling and a suitable charge density of about 35 mC cm−2. Thus, the presented oxide-based alloy offers a beneficial performance as an ion storage layer in electrochromic devices.