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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With the implementation of a relativistic Korringa-Kohn-Rostoker Green's function and band-structure method, we analyze the spin-expectation value of the electron states on the Fermi surface of nonmagnetic as well as magnetic metals. It is shown that for relatively light elements such as Cu the spin states are well defined. A separation of all electron states to "up" and "down" spin-polarized states can be done even in the case of quite heavy but monovalent elements such as Au. In contrast, for heavy polyvalent metals such as Pt, the expectation value of the spin operator can be close to zero in large regions of the Fermi surface. In this case the nonrelativistic language of well-defined "spin-up" and "spin-down" states is not valid anymore. For magnetic materials, the relativistic Fermi surfaces change their topology with respect to the nonrelativistic majority and minority sheets because of spin-orbit driven avoided crossings of the bands. As a result, regions with vanishing spin polarization appear.

We found a strong influence of the composition of the magnetic material on the temperature dependence of the tunneling magneto-Seebeck effect in M gO based tunnel junctions. We use ab initio alloy theory to consider different F exCo1−x alloys for the ferromagnetic layer. Even a small change of the composition leads to strong changes in the magnitude or even in the sign of the tunneling magneto-Seebeck effect. This can explain differences between recent experimental results. In addition, changing the barrier thickness from six to ten monolayers of M gO leads also to a nontrivial change of the temperature dependence. Our results emphasize that the tunneling magnetoSeebeck effect depends very crucially and is very sensitive to material parameters and show that further experimental and theoretical investigations are necessary. The recently theoretically predicted [1] and experimentally confirmed [2, 3] tunneling magneto-Seebeck (TMS) effect in M gO based tunnel junctions belongs to the new field of spin caloritronics [4,5]. In this field the spin-dependent charge transport is combined with energy or heat transport. This means that the spin degree of freedom is exploited in thermoelectrics [6]. Besides the TMS currently investigated effects in the field of spin caloritronics are the spin-Seebeck effect [7,8], the magneto-Seebeck effect in metallic multilayers [9], the thermal spin-transfer torque [10], the spin-dependent Seebeck effect [11], thermally excited spin-currents [12], and the magneto-Peltier cooling [13]. In this letter we investigate the role of the ferromagnetic lead material on the TMS. We show that not only the temperature dependence but even the sign of the TMS effect depends crucially on the material composition.The TMS effect is the change of the Seebeck coefficient with a change of the magnetic orientation of the ferromagnetic leads relative to each other in a tunnel junction. The size of the effect is given by the TMS ratio

We present an implementation of the steady state Keldysh approach in a Green's function multiple scattering scheme to calculate the non-equilibrium spin density. This density is used to obtain the spin-transfer torque in junctions showing the magnetoresistance effect. We use our implementation to study the spin-transfer torque in metallic Co/Cu/Co junctions.