H_c_3 for a thin-film superconductor with a ferromagnetic dot

TL;DR

This paper studies how a ferromagnetic dot influences the upper critical magnetic field in a thin-film superconductor, revealing dependencies on dot properties that can enhance superconducting resilience.

Contribution

It introduces a real-space method to analyze the impact of ferromagnetic dots on H_c_3, highlighting key factors that maximize this critical field.

Findings

H_c_3 can be significantly greater than H_c_2.

Maximal H_c_3 occurs with high dot saturation magnetization.

Optimal enhancement when dot thickness and diameter are comparable.

Abstract

We investigate the effect of a ferromagnetic dot on a thin-film superconductor. We use a real-space method to solve the linearized Ginzburg-Landau equation in order to find the upper critical field, H_c_3. We show that H_c_3 is crucially dependent on dot composition and geometry, and may be significantly greater than H_c_2. H_c_3 is maximally enhanced when (1) the dot saturation magnetization is large, (2) the ratio of dot thickness to dot diameter is of order one, and (3) the dot thickness is large.