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In general, it is difficult to access the thermal conductivity of thin insulating films experimentally by electrical means. Here, we present a new approach utilizing the tunnel magneto-Seebeck effect (TMS) in combination with finite-element modeling (FEM). We detect the laser-induced TMS and the absolute thermovoltage of laser-heated magnetic tunnel junctions with 2.6 nm thin barriers of MgAl2O4 (MAO) and MgO, respectively. A second measurement of the absolute thermovoltage after a dielectric breakdown of the barrier grants insight into the remaining thermovoltage of the stack. Thus, the pure TMS without any parasitic Nernst contributions from the leads can be identified. In combination with FEM via COMSOL, we are able to extract values for the thermal conductivity of MAO (0.7 W (K · m)−1) and MgO (5.8 W (K · m)−1), which are in very good agreement with theoretical predictions. Our method provides a new promising way to extract the experimentally challenging parameter of the thermal conductivity of thin insulating films. [ABSTRACT FROM AUTHOR]

As a platinum group metal, iridium (Ir) is the scarcest element on the earth but it has been widely used as an antiferromagnetic layer in magnetic recording, crucibles and spark plugs due to its high melting point. In magnetic recording, antiferromagnetic layers have been used to pin its neighbouring ferromagnetic layer in a spin-valve read head in a hard disk drive for example. Recently, antiferromagnetic layers have also been found to induce a spin-polarised electrical current. In these devices, the most commonly used antiferromagnet is an Ir–Mn alloy because of its corrosion resistance and the reliable magnetic pinning of adjacent ferromagnetic layers. It is therefore crucial to explore new antiferromagnetic materials without critical raw materials. In this review, recent research on new antiferromagnetic Heusler alloys and their exchange interactions along the plane normal is discussed. These new antiferromagnets are characterised by very sensitive magnetic and electrical measurement techniques recently developed to determine their characteristic temperatures together with atomic structural analysis. Mn-based alloys and compounds are found to be most promising based on their robustness against atomic disordering and large pinning strength up to 1.4 kOe, which is comparable with that for Ir–Mn. The search for new antiferromagnetic films and their characterisation are useful for further miniaturisation and development of spintronic devices in a sustainable manner. [ABSTRACT FROM AUTHOR]

We present a study of the tunnel magneto-Seebeck (TMS)4 effect in MgO based magnetic tunnel junctions (MTJs). The electrodes consist of CoFeB with in-plane magnetic anisotropy. The temperature gradients which generate a voltage across the MTJs layer stack are created using laser heating. Using this method, the temperature can be controlled on the micrometer length scale: here, we investigate, how both, the TMS voltage and the TMS effect, depend on the size, position and intensity of the applied laser spot. For this study, a large variety of different temperature distributions was created across the junction. We recorded 2D maps of voltages generated by heating in dependence of the laser spot position and the corresponding calculated TMS values. The voltages change in value and sign, from large positive values when heating the MTJ directly in the centre to small values when heating the junction on the edges and even small negative values when heating the sample away from the junction. Those zero crossings lead to very high calculated TMS ratios. Our systematic analysis shows, that the distribution of the temperature gradient is essential, to achieve high voltage signals and reasonable resulting TMS ratios. Furthermore, artefacts on the edges produce misleading results, but also open up further possibilities of more complex heating scenarios for spincaloritronics in spintronic devices. [ABSTRACT FROM AUTHOR]