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

最近铁磁性金属中自旋相关塞贝克系数（SSE）的发现立即引发了大规模的研究活动。现在在磁性半导体中也观察到了这种效应。令人惊讶的是，被pt条纹覆盖的绝缘铁磁体在反自旋霍尔效应（ISHE）中也产生了相应的信号，用于观察SSE。特别是后一种观察需要在绝缘体（本例中为LaY2Fe5O12）和金属（Pt）之间引入热激活的界面自旋交换。我们建议通过比较四种类型的样品来研究SSE：具有已知自旋极化的经典铁磁体，高度自旋极化的Heusler合金（接近从铁磁性金属到顺磁性半导体的相变）和REYZ Heusler化合物（RE：稀土，Y=Au, Pt），由于其能带反转而成为拓扑绝缘体。对于选定的样品，我们建议在铁磁体和探测金属之间额外引入薄间隔层：隧道势垒或4f金属（如Tb）。将制备相应的薄膜器件，并使用带有Pt或Pd覆盖条纹的ISHE来表征样品的性质。现有的仪器将被扩展到能够测量SSE的温度依赖性。从这些实验中，我们期望首先对理解带结构对SSE的影响做出贡献。其次，我们希望获得铁磁体与探测金属之间界面影响的实验数据。隧穿势垒应起到去耦间隔的作用，并且预期随着势垒厚度的增加，ISHE信号会衰减。4f-金属应该以反铁磁耦合到底层的铁磁体，因此应该发生ISHE的信号反转，同样具有一定但未知的衰减长度。

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.