Spin-Torque-Biased Magnetic Strip: Nonequilibrium Phase Diagram and Relation to Long Josephson Junctions

Daniel Hill; Se Kwon Kim; Yaroslav Tserkovnyak

doi:10.1103/PhysRevLett.121.037202

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Spin-Torque-Biased Magnetic Strip: Nonequilibrium Phase Diagram and Relation to Long Josephson Junctions

Daniel Hill, Se Kwon Kim, Yaroslav Tserkovnyak

DOI 10.1103/PhysRevLett.121.037202 · Physical Review Letters

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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 superfluidlike transport phenomena in insulating magnetic systems. We study a 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 has the potential for producing applications with superconductor-based circuit functionality at elevated temperatures. The results apply equally to antiferromagnets with suitable effective free energy in terms of the Néel order instead of in-plane magnetization.