Spin screening of magnetic moments in superconductors

TL;DR

This paper investigates how superconductors can screen magnetic moments of embedded ferromagnetic particles through spin polarization, potentially achieving full screening and surpassing traditional Meissner effect mechanisms.

Contribution

It introduces a new spin-based screening mechanism in superconductors that can fully counteract the magnetic moments of ferromagnetic particles.

Findings

Full magnetic moment screening in small ferromagnetic grains at low temperatures.

Spin screening can be stronger than Meissner current screening in type II superconductors.

Induced magnetic moments in the superconductor oppose the ferromagnetic particle's moment.

Abstract

We consider ferromagnetic particles embedded into a superconductor and study the screening of their magnetic moments by the spins of the Cooper pairs in the superconductor. It is shown that a magnetic moment opposite to the one of the ferromagnetic particle is induced in the superconductor. In the case of a small itinerant ferromagnet grain and low temperatures the full screening of the magnetic moment takes place, \textit{% i.e} the absolute value of the total magnetic moment induced in the superconductor is equal to the one of the ferromagnetic particle. In type II superconductors the proposed screening by spins of the conduction electrons can be much stronger than the conventional screening by Meissner currents.