Creating temperature gradients in magnetic nanostructures has resulted in a new research direction, that is, the combination of magneto- and thermoelectric effects. Here, we demonstrate the observation of one important effect of this class: the magneto-Seebeck effect. It is observed when a magnetic configuration changes the charge-based Seebeck coefficient. In particular, the Seebeck coefficient changes during the transition from a parallel to an antiparallel magnetic configuration in a tunnel junction. In this respect, it is the analogue to the tunnelling magnetoresistance. The Seebeck coefficients in parallel and antiparallel configurations are of the order of the voltages known from the charge-Seebeck effect. The size and sign of the effect can be controlled by the composition of the electrodes' atomic layers adjacent to the barrier and the temperature. The geometric centre of the electronic density of states relative to the Fermi level determines the size of the Seebeck effect. Experimentally, we realized 8.8% magneto-Seebeck effect, which results from a voltage change of about -8.7 μV K⁻¹ from the antiparallel to the parallel direction close to the predicted value of -12.1 μV K⁻¹. In contrast to the spin-Seebeck effect, it can be measured as a voltage change directly without conversion of a spin current.

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MgO-based magnetic tunnel junctions with up to 230% tunnel magnetoresistance ratio at room temperature and up to 345% at 13 K are prepared. The lower electrode is either exchange-biased or free, while the top electrode is free or an exchanged-biased artificial ferrimagnet, respectively. Additionally, a pseudo-spin-valve ͑hard-soft switching͒ design with two unpinned electrodes is used. Inelastic electron-tunneling spectra for each of these systems show a strong variation in the zero-bias anomaly with a reduced peak for some of the junctions. At voltages around 200 mV additional structures are found, which are not known from junctions with lower magneto resistance, such as alumina-based junctions. We discuss the spectra for the different electrode types and compare our findings with respect to barrier material and magnetoresistance ratio.

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.

Magnetic tunnel junctions for spin-transfer torque switching were prepared to investigate the dielectric breakdown. The breakdown occurs typically at voltages not much higher than the switching voltages, a bottleneck for the implementation of spin-transfer torque Magnetic Random Access Memory. Intact and broken tunnel junctions are characterized by transport measurements and then prepared for transmission electron microscopy and energy dispersive x-ray spectrometry by focussed ion beam. The comparison to our previous model of the electric breakdown for thicker MgO tunnel barriers reveals significant differences arising from the high current densities.