Spin- and Magneto-Seebeck effects in novel magnetic thin film materials

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The recent discovery of a Spin Dependent Seebeck Coefficient (SSE) in ferromagnetic metals has immediately initiated large research activities. The effect now has been also observed in magnetic semiconductors. Surprisingly, also insulating ferromagnets covered by a Pt-stripe produced corresponding signals in the Inverse Spin Hall Effect (ISHE) which is used to observe the SSE. In particular the latter observation required to introduce a thermally activated interface spin exchange between the insulator (LaY2Fe5O12 in this case) and the metal (Pt). We propose to investigate the SSE by a comparison of four types of samples: Classical ferromagnets with known spin polarization, highly spin polarized Heusler alloys which are close to a phase transition from ferromagnetic metal to paramagnetic semiconductor and REYZ Heusler compounds (RE: Rare Earth, Y=Au, Pt) which are topological insulators due to their band inversion. For selected samples, we propose to additionally introduce thin spacer layers between the ferromagnet and the detecting metal: a tunnel barrier or a 4f-metal such as Tb. The corresponding thin film devices will be prepared and the ISHE with a Pt or a Pd cover stripe will be used to characterize the sample properties. The existing apparatus will be extended to enable also measurements of the temperature dependence of the SSE. From these experiments, we expect first a contribution to the understanding of the influence of the band structure on the SSE. Second, we hope to gain experimental data about the influence of the interfaces between the ferromagnet and the detector metal. The tunneling barriers should act as decoupling spacers and a decay of the ISHE signal with increasing barrier thickness is expected. The 4f-metal should couple antiferromagnetically to the underlying ferromagnet and thus a sign reversal of the ISHE should occur, again with a certain but yet unknown attenuation length.