‘Spin caloritronics’ is a burgeoning field of study which studies interactions between heat, electrons, and magnetism in solids (Fig. 1). The field was initiated with the discovery of the spin-Seebeck effect (SSE) in 2008 , and has evolved with diverse research topics which lead to the discovery of novel effects, such as spin-dependent Seebeck effect , spin-Peltier effect , etc.
Figure 1. Concept of spin-caloritronics
The SSE is the conversion of heat (or a temperature gradient) into electricity like the charge-based thermoelectric effect, but it utilizes electron ‘spin’ instead of charge. The additional spin degree-of-freedom not only provides a larger parameter space for optimizing the device performance, but also enables new device design which could overcome the shortcomings of the existing thermoelectric devices. While a SSE device possesses the same advantages (no moving parts, long life time, high power density, etc.) with those conventional thermoelectric devices have, the use of electron spin and the resulting device geometry make it possible to separately tune the thermal conduction and electrical conduction in the device, which has been one of the biggest challenges in conventional thermoelectric devices. Also, the fact that the temperature gradient and the electrical output are perpendicular to each other makes it possible to use only one type of material, whereas conventional thermoelectric devices require two different types of materials (e.g. n- and p-type semiconductors) (Fig. 2).
Figure 2. Structural differences between Seebeck effect and spin Seebeck effect
Our group aims to develop efficient thermoelectric devices utilizing a variety of spin-caloritronic effects. We conduct fundamental research to better understand interactions between heat, electrons, and magnetism in solids, and to find interesting novel phenomena based on it. We also try to employ novel device designs by introducing those newly discovered phenomena as well as new materials.
1. K. Uchida et al., Observation of the spin Seebeck effect, Nature, 455, 7214 (2008).
2. A. Slachter et al., Thermally driven spin injection from a ferromagnet into a non-magnetic metal, Nature Phys, 6, 879–882 (2010)
3. J. Flipse et al., Direct observation of the spin-dependent Peltier effect, Nature Nanotech, 7, 166–168 (2012).