Easy-Plane Magnetic Strip as a Long Josephson Junction

TL;DR

This paper demonstrates that an easy-plane ferromagnetic strip can emulate a long Josephson junction, enabling superfluid-like transport phenomena in magnetic systems through a novel theoretical mapping.

Contribution

It introduces a theoretical model mapping an easy-plane ferromagnet to a long Josephson junction, revealing new ways to realize superfluid-like transport in magnetic insulators.

Findings

Mapped EPF dynamics to LJJ model

Derived phase diagram for static multidomain phases

Proposed superconducting circuit analogs at higher temperatures

Abstract

Spin-torque-biased magnetic dynamics in an easy-plane ferromagnet (EPF) is theoretically studied in the presence of a weak in-plane anisotropy. While this anisotropy spoils U(1) symmetry thereby quenching the conventional spin superfluidity, we show that the system instead realizes a close analog of a long Josephson junction (LJJ) model. The traditional magnetic-field and electric-current controls of the latter map respectively onto the symmetric and antisymmetric combinations of the out-of-plane spin torques applied at the ends of the magnetic strip. This suggests an alternative route towards realizations of superfluid-like transport phenomena in insulating magnetic systems. We study spin-torque-biased phase diagram, providing an analytical solution for static multidomain phases in the EPF. We adapt an existing self-consistency method for the LJJ to develop an approximate solution for the EPF dynamics. The LJJ-EPF mapping allows us to envision superconducting circuit functionality at elevated temperatures. The results apply equally to antiferromagnets with suitable effective free energy in terms of the N\'{e}el order instead of magnetization.