Enhancement of critical current density in superconducting/magnetic multilayers with slow magnetic relaxation dynamics and large magnetic susceptibility

Abstract

We propose to use a superconductor-magnet multilayer structure to achieve high critical current density by invoking the polaronic mechanism of pinning. The magnetic layers should have large magnetic susceptibility to enhance the coupling between the vortices and magnetization in those layers. The relaxation of the magnetization should be slow. When the velocity of vortices is low, they are dressed by nonuniform magnetization and move as polarons. In this case, the viscosity of vortices, which is proportional to the magnetic relaxation time, is enhanced significantly. As the velocity increases, the polarons dissociate and the viscosity drops to the usual Bardeen-Stephen value, resulting in a jump in the I-V curve. Experimentally the jump shows up as a depinning transition and the corresponding current at the jump is the depinning current. For Nb and an appropriate magnet multilayer structure, we estimate the critical current density Jc∼109A/m2 at magnetic field B≈1 T.

Source-reported materials — not catalogue approval

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