Abwärme als Energiequelle

Die Verstromung von Abwärme ist ein vielversprechender Ansatz zur Steigerung der Energieeffizienz vieler Prozesse. Hierfür bietet die Thermoelektrik große Vorteile in Bezug auf Systemkomplexität, Wartungsfreiheit und Langzeitstabilität. In den letzten Jahren wurden neue, effizientere thermoelektrische Materialien entwickelt. Auch die Aufbautechnik wurde verbessert. Auf dieser Basis werden nun thermoelektrische Module in Systemen verschiedener Anwendungen erprobt. Dazu zählen Fahrzeuge, Blockheizkraftwerke und die industrielle Abwärmenutzung zum Beispiel in Stahlwerken. Durch Produktion im industriellen Maßstab kann die Thermoelektrik zukünftig so wirtschaftlich werden, dass sie auf vielen Anwendungsgebieten einen spürbaren Beitrag zur Senkung der CO₂‐Emissionen leistet.     

Spin-transfer torque in tunnel junctions with ferromagnetic layer of finite thickness

Two components of the spin torque exerted on a free ferromagnetic layer of finite thickness and a half-infinite ferromagnetic electrode in single tunnel junctions have been calculated in the spin-polarized free-electron-like one-band model. It has been found that the torque oscillates with the thickness of ferromagnetic layer and can be enhanced in the junction with the special layer thickness. The bias dependence of torque components also significantly changes with layer thickness. It is non-symmetric for the normal torque, in contrast to the symmetric junctions with two identical half-infinite ferromagnetic electrodes. The asymmetry of the bias dependence of the normal component of the torque can be also observed in the junctions with different spin splitting of the electron bands in the ferromagnetic electrodes.     

The observation of inherent spin Seebeck effect in Rh/YIG hybrid structure

Rhodium (Rh) is a 4d metal possessing a large spin orbit coupling strength and spin-Hall conductivity with a very small magnetic susceptibility, implying an insignificant magnetic proximity effect (MPE). We report here the observation of longitudinal spin Seebeck effect (LSSE) using Rh as a normal metal. A Rh film was sputtered on nanometer thick YIG films of highly crystalline nature and extremely low magnetic damping to obtain Rh/YIG hybrid structure. A clear thermal voltage V_th (SSE voltage) was obtained when a temperature gradient was applied on the Rh/YIG hybrid. The Rh film showed a very weak anomalous Hall resistance and the magneto-resistive testing clearly ruled out the magnetization of the Rh films via MPE. The anisotropic magnetoresistance (AMR) revealed a clear spin hall magnetoresistance (SMR) signal in Rh film implying a purely intrinsic spin current generation, free from any parasitic magnetic effects. The work can open a new window in the study of pure and uncontaminated spin current, generated in ferromagnetic insulators, using Rh as spin current detector.