Controlled switching between paramagnetic and diamagnetic Meissner effect in Pb/Co nanocomposites

TL;DR

This study demonstrates controllable switching between diamagnetic and paramagnetic Meissner effects in Pb/Co nanocomposites, revealing new magnetic behaviors due to vortex formation and ferromagnetic particle alignment.

Contribution

It introduces a hybrid Pb/Co system exhibiting tunable magnetic responses, combining superconductivity with ferromagnetic particles to control vortex states.

Findings

Switchable diamagnetic and paramagnetic Meissner effects observed.

Positive magnetization amplified below T_c.

Vortex formation linked to ferromagnetic particle alignment.

Abstract

A hybrid system which consists of a superconducting (SC) Pb film (100 nm thickness) containing $\sim$1 vol% single domain ferromagnetic (FM) Co particles of mean-size $\sim$4.5 nm reveal unusual magnetic properties: (i) a controlled switching between the usual diamagnetic and the unusual paramagnetic Meissner effect in field cooling as well as in zero-field cooling experiments (ii) amplification of the positive magnetization when the sample enters the SC state below T$_c$. These experimental findings can be explained by the formation of spontaneous vortices and the possible alignment of these vortices due to the foregoing alignment of the Co particle FM moments by an external magnetic field.