Critical Current Oscillations of Josephson Junctions Containing PdFe Nanomagnets

TL;DR

This study investigates how the critical current in Josephson junctions with PdFe ferromagnetic layers oscillates with barrier thickness, revealing phase transitions between 0 and π states relevant for cryogenic memory.

Contribution

It demonstrates the oscillatory behavior of critical current in Josephson junctions containing PdFe alloys, highlighting phase transitions useful for memory device applications.

Findings

Critical current oscillates with ferromagnetic layer thickness.

Transitions between 0 and π phase states observed.

Fraunhofer patterns confirm phase shifts.

Abstract

Josephson junctions with ferromagnetic layers are vital elements in a new class of cryogenic memory devices. One style of memory device contains a spin valve with one "hard" magnetic layer and one "soft" layer. To achieve low switching fields, it is advantageous for the soft layer to have low magnetization and low magnetocrystalline anisotropy. A candidate class of materials that fulfills these criteria is the Pd$_{1-x}$Fe$_{x}$ alloy system with low Fe concentrations. We present studies of micron-scale elliptically-shaped Josephson junctions containing Pd$_{97}$Fe$_{3}$ layers of varying thickness. By applying an external magnetic field, the critical current of the junctions are found to follow characteristic Fraunhofer patterns. The maximum value of the critical current, extracted from the Fraunhofer patterns, oscillates as a function of the ferromagnetic barrier thickness, indicating transitions in the phase difference across the junction between values of zero and $\pi$.