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.

Antiferromagnetic semiconductors are new alternative materials for spintronic applications and spin valves. In this work, we report a detailed investigation of two antiferromagnetic semiconductors AMnAs (A = Li, LaO), which are isostructural to the well-known LiFeAs and LaOFeAs superconductors. Here we present a comparison between the structural, magnetic, and electronic properties of LiMnAs, LaOMnAs, and related materials. Interestingly, both LiMnAs and LaOMnAs show a variation in resistivity with more than five orders of magnitude, making them particularly suitable for use in future electronic devices. Neutron and x-ray diffraction measurements on LiMnAs show a magnetic phase transition corresponding to the Néel temperature of 373.8 K, and a structural transition from the tetragonal to the cubic phase at 768 K. These experimental results are supported by density functional theory calculations.

The transport properties of Co 2 MnSi/ AlO x / Co-Fe magnetic tunnel junctions showing a tunnel magnetorestistance of 95% at low temperatures are discussed with respect to temperature-dependent magnetic moments at the Co 2 MnSi/ AlO x interface and electronic band structure effects. These junctions show a considerably larger temperature and bias voltage dependence of the tunneling magnetoresistance compared to Co-Fe -B/AlO x / Co-Fe-B junctions, although the effective spin polarization of Co 2 MnSi ͑66%͒ is larger than CoFe-B ͑60%͒. Especially, the tunnel magnetoresistance of the Co 2 MnSi based junctions becomes inverse for large bias voltages. With increasing atomic disorder of the interfacial Co 2 MnSi its magnetic moments decrease and show a stronger temperature dependence. Even for the best atomic ordering achieved the corresponding spin-wave parameters of Mn and Co at the Co 2 MnSi/ AlO x interface are significantly larger than expected for Co 2 MnSi bulk and also larger than the spin-wave parameters of Co and Fe at a Co-Fe-B / AlO x interface. The influence of enhanced interfacial magnon excitation in the Co 2 MnSi/ AlO x / Co-Fe junctions on their transport properties will be discussed as well as possible origins for the negative tunnel magnetoresistance at high bias voltages.

Interest in femtosecond demagnetization dynamics was sparked by Bigot's experiment in 1996, which unveiled the elementary mechanisms that relate the electrons' temperature to their spin order. Simultaneously, the application of fast demagnetization experiments has been demonstrated to provide key insight into technologically important systems such as high-spin-polarization metals, and consequently there is broad interest in further understanding the physics of these phenomena. To gain new and relevant insights, we performed ultrafast optical pump-probe experiments to characterize the demagnetization processes of highly spin-polarized magnetic thin films on a femtosecond time scale. Full spin polarization is obtained in half-metallic ferro-or ferrimagnets, where only one spin channel is populated at the Fermi level, whereas the other one exhibits a gap. In these materials, the spin-scattering processes is controlled via the electronic structure, and thus their ultrafast demagnetization is solely related to the spin polarization via a Fermi golden-rule model. Accordingly, a long demagnetization time correlates with a high spin polarization due to the suppression of the spin-flip scattering at around the Fermi level. Here we show that isoelectronic Heusler compounds (Co 2 MnSi, Co 2 MnGe, and Co 2 FeAl) exhibit a degree of spin polarization between 59% and 86%. We explain this behavior by considering the robustness of the gap against structural disorder. Moreover, we observe that CoFe-based pseudogap materials, such as partially ordered Co-Fe-Ge and Co-Fe-B alloys, can reach similar values of the spin polarization. By using the unique features of these metals we vary the number of possible spin-flip channels, which allows us to pinpoint and control the half-metals' electronic structure and its influence on the elementary mechanisms of ultrafast demagnetization.Since the discovery of ultrafast demagnetization processes on femtosecond time scales, the underlying mechanism has been under debate [1,2]. However, the last few years have seen the development of the first quantitative models, such as the microscopic three-temperature model [3], the stochastic Landau-Lifshitz-Bloch equation describing averaged spin ensembles [4,5], and stochastic atomistic descriptions [6]. These models suggest that the spin-scattering el-sp is related to the Gilbert damping parameter that describes the energy dissipation of the magnetic system in quasiequilibrium via the same elementary spin-flip processes [7]. The Gilbert damping tends to be small in half-metals where the elementary spin-flip processes are blocked [8]. Just recently, progress in the ab initio description of Gilbert damping has been made [9], shedding additional light onto a long-standing issue. By correlating the experimentally observed values of the Gilbert damping parameter to the coupling parameter of the magnetic system (magnons) and the electron temperature, the Landau-Lifshitz-Bloch model allows the quantitative description of ultrafast demagnetization versus time wi...

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