Optimized thickness of superconducting aluminum electrodes for measurement of spin polarization with MgO tunnel barriers

Superconducting tunneling spectroscopy (STS) is one of the most useful techniques for measuring the tunneling spin polarization of magnetic materials, typically carried out using aluminum electrodes. Recent studies using MgO barriers have shown the extreme sensitivity of the spin polarization to annealing at temperatures up to $∼400°C$⁠. Here the authors show that by optimizing the thickness of aluminum superconducting electrodes, STS measurements can be carried out even for such high annealing temperatures.