Thermal conductance in spin caloritronics
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Abstract
Spin caloritronics is a field of research that relates the interaction of the electronic spin to a heat flow in a sample. Since the magnitude of such a heat flow is only quantifiable with precise knowledge of the thermal conductivity of the sample, this thesis studies the role of the thermal conductivity in spin caloritronics. However, the 3 omega method as developed by Cahill et al. that isrncommonly used to determine the thermal conductivity in thin films is only capable of analyzing films with a thermal conductivity much lower than that of the substrate.rnThis thesis describes and applies a suitable extension of the original 3 omega method that eliminates these shortcomings. So far, determining the thermal conductivity by this extension led to large numerical uncertainties. The novel data evaluation scheme presented here is based on Bayesian statistics in order to reduce the numerical instability.rnWhile the majority of the projects within spin caloritronics considers the impact of a temperature gradient applied to a solid on the spin structure, this project analyzes the inverse question: How does a change in magnetic texture change the thermal conductivity of a material? In particular, such an effect of a magnetic field on the thermal conductivity was studied concerning thermal transport perpendicular to the film plane in La0.67Ca0.33MnO3 and in the film plane in Permalloy. In both cases the measured change in thermal conductivity inrnthe presence of a magnetic field is discussed.rnFinally, as explained, the community of spin caloritronics relies on accurate values of the thin film thermal conductivity of a number of characteristic materials. Especially Y3Fe5O12 (YIG) is studied frequently, so that as an example of particular interest the thin film thermal conductance of YIG is presented and analyzed. The methods and results presented here provide a different approach to spin caloritronic research and allow a novel path to studying thermal conductivity.