Experiments on giant thermal magnetogalvanic efects in magnetic tunnel junctions

在横向器件和巨磁阻（GMR）纳米柱结中发现了自旋依赖的塞贝克效应。在自旋扩散的尺度上，热驱动的自旋积累导致了长度上的磁热能。自旋波激发也有助于在毫米量级的长度上热驱动磁热电能。我们将重点研究巨隧道磁阻（TMR）器件（Heusler/MgO/Heusler和Co-Fe-B/MgO/Co-Fe-B），其TMR值高达bb0 ~ 200%。首先，热隧穿电流的强自旋不对称性导致化学势的自旋相关位移。在与一个理论项目的合作中，预测了~60 μV的高磁热电功率（MTEPs），并表现出特殊的温度依赖性。其次，非弹性隧道过程可以在半金属结中打开隧道通道，反映隧道势垒两侧不同的磁振子温度。为了确定巨隧穿磁阻（TMR）器件中自旋相关的塞贝克系数，我们将开发通过电阻和光学加热在隧道结中产生温度梯度的技术。此外，我们将为进行静态加热奠定基础，静态加热只允许在隧道势垒处温度下降十分之一度的非常小的温度梯度，而且还将进行纳秒电脉冲和飞秒光激发的动态实验。我们的目标是与我们的理论合作者密切合作，了解高自旋相关塞贝克系数的起源，这是由巨大隧道磁电阻器件中隧穿概率的强自旋不对称引起的。

Spin-dependent Seebeck effects have been discovered in lateral devices and giant-magnetoresistance (GMR) nanopillar junctions. Thermally driven spin accumulation leads to a magnetothermopower over length on the scale of the spin diffusion. Spin-wave excitations also contribute to thermally driven magnetothermopower over length on the order of millimeters. We will focus on giant-tunneling-magnetoresistance (TMR) devices (Heusler/MgO/Heusler and Co-Fe-B/MgO/Co-Fe-B) with high TMR values of >200%. First, the strong spin asymmetry of the thermal tunneling current leads to a spin-dependent shift of the chemical potential. In joint collaboration with a theory project, high magnetothermopowers (MTEPs) of ~60 μV have been predicted to and show peculiar temperature dependence. Second, inelastic tunneling processes may open tunneling channels in half-metallic junctions, mirroring the different magnon temperatures on both side of the tunnel barrier. To determine the spin-dependent Seebeck coefficients in giant tunneling magnetoresistance (TMR) devices, we will develop techniques to generate temperature gradients in tunnel junctions by resistive and optical heating. In addition, we will lay the foundation to perform not only static heating, which allows only very small temperature gradients of a one tenth of a degree temperature drop at the tunnel barrier, but also dynamic experiments with nanosecond electrical pulses and femtosecond optical excitation. Our aim is to understand, in close collaboration with our theoretical collaborator, the origin of high spin-dependent Seebeck coefficients arising from strong spin asymmetries of the tunneling probability in giant tunneling magnetoresistance devices.