Spin-current-induced modification of the thermal Boltzmann distribution in paramagnetic and ferromagnetic nanostructures

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It has been recently demonstrated that spin-polarized currents which flow through magnetic nano-devices result in an effective cooling of the spin system. Such direct effects of spin-polarized currents, like the spin-Seebeck or Peltier effect, correlate spin currents with temperature gradients. In this project we aim at studying the cooling of paramagnetic systems induced by spin-polarized currents. Microwave irradiation under electron spin resonance (ESR) conditions will be used to saturate the spin-up and spindown states in a paramagnet grown on a ferromagnetic spin injector. The spinpolarized currents are expected to change the balance of the different spin-states resulting in an effective cooling indicated by the appearance of the ESR signal. The ESR will be detected by microwave absorption and thermal response of the system, providing a measure for the absorption to emission ratio. Such systems can be considered as prototype devices for spin current induced cooling of quantum dot systems and microwave- controlled spintronic devices. The latter bears the potential to be operational using very low current densities. Another advantage of the proposed method is the potential to fully characterize the magnetic high-frequency susceptibility and anisotropy of the ferromagnetic electrodes, which are used as spin polarisers. A full set of static and dynamic magnetic parameters of all magnetically active constituents, including the temperature dependence, element specificity via specific transitions and in-situ measurements during growth will be experimentally determined.