Planar Superconductor-Ferromagnet-Superconductor Josephson junctions as scanning probe sensors

TL;DR

This paper introduces a new magnetic scanning probe sensor based on a planar Josephson junction with a magnetic barrier, offering enhanced sensitivity and resolution compared to traditional SQUID sensors.

Contribution

It presents a novel planar Josephson junction design with magnetic barriers that improves flux focusing and sensor performance, including miniaturization and self-field amplification.

Findings

Sensor prototypes with CuNi and Ni barriers demonstrate high sensitivity.

Planar geometry enables easy miniaturization to nanometer scale.

Self-field phenomenon enhances sensitivity and allows simple feedback implementation.

Abstract

We propose a novel type of magnetic scanning probe sensor, based on a single planar Josephson junction with a magnetic barrier. The planar geometry together with high magnetic permeability of the barrier helps to focus flux in the junction and thus enhance the sensitivity of the sensor. As a result, it may outperform equally sized SQUID both in terms of the magnetic field sensitivity and the spatial resolution in one scanning direction. We fabricate and analyze experimentally sensor prototypes with a superparamagnetic CuNi and a ferromagnetic Ni barrier. We demonstrate that the planar geometry allows easy miniaturization to nm-scale, facilitates an effective utilization of the self-field phenomenon for amplification of sensitivity and a simple implementation of a control line for feed-back operation in a broad dynamic range.