Spin Seebeck effects (SSEs) have been investigated in highly crystalline magnetic multilayer [Fe 3 O 4 /Pt] n films. Voltage as well as power generated by the SSE were found to be significantly enhanced with increasing the number of layers n. This voltage enhancement defies the simple understanding of the SSE and suggests that spin current flowing between the magnetic layers in the thickness direction plays an important role in multilayer SSE systems and the observed voltage enhancement.

We report a complete characterization of the anomalous Nernst effect (ANE) and its relationship with the anomalous Hall effect (AHE) in Fe 3 O 4 . By combining full thermoelectric and electric transport measurements as a function of temperature, we have verified that the universal scaling relation between the anomalous Hall and diagonal conductivities (σ zy ∝ σ 1.6 zz ), observed in materials with bad-metal-hopping type of conduction, is also applicable to the thermoelectric transport. We further show that the ANE and AHE are commonly related through the Mott relation, therefore demonstrating its validity for anomalous transport phenomena in materials with conduction in the the dirty regime.

Terahertz emission spectroscopy (TES) of ultrathin multilayers of magnetic and heavy metals has recently attracted much interest. This method not only provides fundamental insights into photoinduced spin transport and spin-orbit interaction at highest frequencies, but has also paved the way for applications such as e±cient and ultrabroadband emitters of terahertz (THz) electromagnetic radiation. So far, predominantly standard ferromagnetic materials have been exploited. Here, by introducing a suitable¯gure of merit, we systematically compare the strength of THz emission from X/Pt bilayers with X being a complex ferro-, ferri-and antiferromagnetic metal, that is, dysprosium cobalt (DyCo 5 ), gadolinium iron (Gd 24 Fe 76 ), magnetite (Fe 3 O 4 ) and iron rhodium (FeRh). We¯nd that the performance in terms of spin-current generation not only depends on the spin polarization of the magnet's conduction electrons, but also on the speci¯c interface conditions, thereby suggesting TES to be a highly interface-sensitive technique. In general, our results are relevant for all applications that rely on the optical generation of ultrafast spin currents in spintronic metallic multilayers.

We report a systematic study on the thermoelectric performance of spin Seebeck devices based on Fe 3 O 4 /Pt junction systems. We explore two types of device geometries: a spin Hall thermopile and spin Seebeck multilayer structures. The spin Hall thermopile increases the sensitivity of the spin Seebeck effect, while the increase in the sample internal resistance has a detrimental effect on the output power. We found that the spin Seebeck multilayers can overcome this limitation since the multilayers exhibit the enhancement of the thermoelectric voltage and the reduction of the internal resistance simultaneously, therefore resulting in significant power enhancement. This result demonstrates that the multilayer structures are useful for improving the thermoelectric performance of the spin Seebeck effect.

arXiv:1911.07549 [cond-mat.mtrl-sci] arXiv:1911.07549 [cond-mat.mtrl-sci]