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

最近已经证明，自旋极化电流流过磁性纳米器件会导致自旋系统的有效冷却。自旋极化电流的这种直接效应，如自旋塞贝克效应或珀尔蒂埃效应，将自旋电流与温度梯度联系起来。在这个项目中，我们的目的是研究自旋极化电流诱导顺磁系统的冷却。在电子自旋共振（ESR）条件下，微波辐射将使在铁磁自旋注入器上生长的顺磁体的自旋上和自旋下状态饱和。预计自旋极化电流将改变不同自旋态的平衡，从而导致ESR信号的出现所表明的有效冷却。ESR将通过系统的微波吸收和热响应来检测，为吸收发射比提供了一个测量指标。这种系统可以被认为是量子点系统和微波控制自旋电子器件的自旋电流诱导冷却的原型装置。后者具有使用极低电流密度即可运行的潜力。该方法的另一个优点是可以充分表征用作自旋极化器的铁磁电极的高频磁化率和各向异性。所有磁性活性成分的一整套静态和动态磁性参数，包括温度依赖性，通过特定转变的元素特异性和生长过程中的原位测量，将通过实验确定。

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.