Magnetic Reversal and Critical Current Transparency of CoFeB Superconductor-Ferromagnet-Superconductor Heterostructures

TL;DR

This study investigates the magnetic and superconducting properties of Nb/CoFeB/Nb heterostructures, revealing how ferromagnetic layer thickness influences critical current and magnetic switching behavior at low temperatures.

Contribution

It provides new insights into the magnetic reversal and critical current transparency in CoFeB-based superconductor-ferromagnet-superconductor heterostructures, including effects of multilayer buffer structures.

Findings

Critical current decays exponentially with ferromagnetic layer thickness.

A dip in critical current at 0.8 nm indicates phase change.

Reduced magnetic switching distributions with multilayer buffers.

Abstract

In this work, we show fundamental low temperature (T) magnetic and Ic responses of a magnetic Josephson Junction (MJJ) S/F/S heterostructure - Nb/ Co56Fe24B20 /Nb. The ultra-thin Co56Fe24B20 (CFB) films (0.6-1.3 nm) were deposited onto two separate buffer layers: 150 nm Nb/5 nm Cu and 150 nm Nb/ (1 nm Cu/0.5 nm Nb)6/1 nm Cu. Both film sets were capped with 5 nm Cu/50 nm Nb. Magnetic results show reduced switching distributions in patterned arrays measured at near liquid Helium temperature (~ 10 K), with the incorporation of the (1 nm Cu/0.5 nm Nb)6/1 nm multilayer. In electrical devices, the critical current (Ic) through the CFB layer decays exponentially with increasing ferromagnetic layer thickness and shows a dip in Ic at 0.8 nm, characteristic of a change in the equilibrium Josephson phase in an S/F/S structure.