Pulsed Spin Torque Switching of Spin-Valves with Dilute Permalloy Free Layers for Cryogenic Applications

Cryogenic spin-transfer spin-valve (CST-SV) devices are considered a potential solution for low-temperature data storage in superconducting computing, due to their low impedance and power consumption, their high speed and large packing density. These devices incorporate Nb electrodes with a synthetic antiferromagnetic reference layer and a Cu-diluted Permalloy (Py) free layer with reduced magnetic moment density, designed to reduce the switching energy. Specifically, we studied 50 nm x 110 nm elliptically shaped in-plane magnetized nanopillars. Quasistatic current-voltage measurements of these devices show a factor of two reduction of average switching currents compared to devices with an undiluted Py free layer, while exhibiting a similar resistance difference between the parallel (P) and antiparallel (AP) magnetic configurations of about 200 mΩ. Both types of devices show sharp switching with coercive fields in the range of 10-40 mT. Using a cryogenic probe station, we investigated pulsed switching with pulses from 0.1 ns to 100 ms and compare the characteristics of undiluted versus diluted Py free layers, including the effective energy barrier heights and their temperature dependence.