Anomalous Nernst effect in Co2MnSi thin films

Separation of the anomalous Nernst and spin Seebeck voltages in bilayer devices is often problematic when both layers are metallic, and the anomalous Nernst effect (ANE) becomes non-negligible. Co2MnSi, a strong candidate for the spin generator in spin Seebeck devices, is a predicted half-metal with 100% spin polarisation at the Fermi energy, however, typically B2 or L21 order is needed to achieve this. We demonstrate the optimisation of thin film growth of Co2MnSi on glass, where choice of deposition and annealing temperature can promote various ordered states. The contribution from the ANE is then investigated to inform futuremeasurements of the spin Seebeck. A maximum ANE coefficient of 0.662 µV K−1 is found for an A2 disordered polycrystalline Co2MnSi film. This value is comparable to ordered Heuslerthin films deposited onto single crystal substrates but obtained at a far lower fabrication temperature and material cost.</div

Spin Seebeck effect in polycrystalline yttrium iron garnet pellets prepared by the solid-state method [Letter]

We study the properties of polycrystalline bulk yttrium iron garnet (YIG) pellets prepared by the solid-state method, where the choice of the sintering temperature can lead to mixed phases of yttrium iron perovskite (YIP) and YIG or single phase YIG. Magnetometry shows multiple switching regimes in the mixed-phase pellets where the saturation magnetization is dominated by the proportion of YIG present. Ferromagnetic resonance was used to corroborate the saturation magnetization from magnetometry and to extract the spin wave damping α. The lowest damping was observed for the YIG pellet, which resulted in a spin Seebeck effect (SSE) coefficient that was approximately 55% of single crystal YIG. This demonstrates that macroscale crystallization does not play a major role in the SSE and paves the way for utilising polycrystalline samples for thermomagnetic applications

Optimisation of Co2MnSi thin films and multilayers for spin Seebeck devices

© 2017 IEEE. The spin Seebeck effect is defined as the generation of a pure spin current (J s ) when a magnetised material is subjected to a temperature gradient (ΔT)

Yttrium iron garnet (YIG) spin Seebeck effect (SSE) study

Magnetic and structural characterisation of YIG pellets prepared via solid state method where the YIG/YIP ratio varied.Includes final figures for journal (origin project) as well as raw data in a zip file.</div

Low Temperature Spin Seebeck Effect (T SSE) rig

Dataset accompanying development of low T SSE (Temperature Spin Seebeck Effect) measurement.Figures.opju contains analysed data used to create figures.Low T SSE.zip contains raw data obtained during measurement.</div

Spin Seebeck FeOx thickness and inelastic neutron scattering study

Data accompanying publication 'Magnon diffusion lengths in bulk and thin film Fe3O4 for spin Seebeck applications' in Physical Review Materials

Enhancement of spin Seebeck effect in Fe3O4/Pt thin films with a-Fe nanodroplets - supporting data

Characterisation data for 80 nm Fe3O4: 5nm Pt samples deposited as a series such that plume texturing results in minor modification of film interface.Origin Project gives analysed data as presented in Figures 1-4.Zip folder includes neutron reflectivity fit outputs described in Figure 5.Raw data for Figure 5 at https://doi.org/10.5286/ISIS.E.RB2010586-1.Funding abstract:As part of the Energy Efficiency Directive, the UK has committed to a 20% increase in energy efficiency, a reduction of greenhouse gas emissions by at least 20% and an increased share of renewable energy sources (compared to 1990 levels) by 2020. To address these challenges a stable and diverse range of energy sources will need to be developed and, unsurprisingly, this has been the focus of an intense international research effort. The associated research challenges can be loosely categorised into renewable sources (solar, wind, tidal), sustainable sources (e.g. carbon capture, fusion), and micro generation (e.g. energy harvesting from thermal, light, sound, or vibrational sources). One example of such sources is the harvesting of waste heat with thermoelectric generators (TEGs), a technology that has the advantage of reliability (no moving parts), but is limited by high costs (use of critical elements such as Te) and low efficiencies (<10% for a 200K temperature difference). Given the abundant sources of waste heat in everyday life (boilers, engines, computers, district heat networks), development of low-cost TEGs that could easily be applied to various surfaces could present a significant vector for change. For example, harvesting just 5% of the energy lost as waste heat by car engines in the UK would save the equivalent of 1 hundred thousand equivalent tonnes of oil per year (or ~1% of the UK's total energy usage in 2014). Conventional TEGs are typically based on the Seebeck effect: a physical process that results in the generation of an electric current when a temperature difference exists between two ends of a material. One of the bottlenecks for improvement of the efficiency of these devices is the co-dependence of two key material properties: the thermal and electric conductivity. Whilst some progress has been made to circumvent this by nano-engineering, there is still some way to go before widespread commercialisation becomes viable. This could, however, be overcome with TEGs based on the spin Seebeck effect, where an additional degree of freedom - the spin of the electrons - results in a device architecture that scales with surface area (unlike conventional thermoelectrics), enables separation of the thermal and electric conductivities that drive the efficiency of the device and boasts active materials that could be sourced from abundant sources (such as iron or copper, rather than bismuth telluride). The aim of this Fellowship is to investigate the spin Seebeck effect with regards to its application as a TEG. There are 5 key challenges that will be addressed: (1) precise determination of the efficiency of such spin Seebeck based TEGs; (2) discovery of new materials (from abundant sources); (3) development of prototype TEGs; (4) identifying the controlling factors with regards to the efficiency of the overall device; and (5) understanding the underlying physics of this effect. For example, harnessing the maximum spin polarised current generated by the spin Seebeck effect typically requires the use of expensive platinum contacts. For such technology to become economically viable would therefore require discovery of cheaper alternatives, such as the doped metals that will be investigated. In addition, precise characterisation of the spin Seebeck effect is limited by instrumentation that typically only monitors the temperature difference (rather than heat flow), hence instrumentation will be developed to monitor both these parameters so that the power conversion can be determined. There is also, as of yet, no comprehensive coefficient that can be used to compare different material systems (such as the Seebeck coefficient for conventional thermoelectrics), nor a rigorously tested figure of merit. Once this has been established, a comprehensive comparison of different materials and engineering of the overall device can be made.</p