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0-pi Josephson tunnel junctions with ferromagnetic barrier
M Weides1, M Kemmler, H Kohlstedt
1Center of Nanoelectronic Systems for Information Technology (CNI), Research Centre Jülich, D-52425 Jülich, Germany. m.weides@fz-juelich.de
Physical Review Letters
|February 7, 2007
Summary
Researchers created superconductor-insulator-ferromagnet-superconductor Josephson junctions exhibiting a spontaneous vortex. This vortex, pinned at a unique step in the ferromagnetic layer, carries a significant fraction of a magnetic flux quantum (Φ0).
Area of Science:
- Condensed Matter Physics
- Superconductivity
- Spintronics
Background:
- Superconductor-ferromagnet-superconductor (SFS) Josephson junctions are crucial for spintronic devices.
- Understanding the behavior of Josephson vortices in engineered SFS structures is key to advancing superconducting electronics.
Purpose of the Study:
- To fabricate and characterize high-quality Nb/Al2O3/Ni(0.6)Cu(0.4)/Nb Josephson tunnel junctions.
- To investigate the properties of 0-pi Josephson junctions with a steplike ferromagnetic layer.
- To analyze the spontaneous vortex formation and its characteristics within the junction.
Main Methods:
- Fabrication of superconductor-insulator-ferromagnet-superconductor (SFS) Josephson tunnel junctions using niobium (Nb) and a Ni(0.6)Cu(0.4) ferromagnetic alloy.
- Utilizing a ferromagnetic layer with a steplike thickness to create a 0-pi junction.
- Measurement of critical current dependence on applied magnetic field.
Main Results:
- Successfully fabricated high-quality Nb/Al2O3/Ni(0.6)Cu(0.4)/Nb Josephson junctions.
- Demonstrated a 0-pi junction with equal 0 and pi sections, characterized by a spontaneous vortex of supercurrent.
- Observed the spontaneous vortex pinned at the 0-pi step, carrying approximately 6.7% of the magnetic flux quantum (Φ0).
- Noted a distinct minimum in critical current near zero applied magnetic field.
Conclusions:
- The engineered steplike ferromagnetic layer effectively creates a 0-pi Josephson junction.
- A spontaneous vortex pinned at the 0-pi step is a stable ground state in these long Josephson junctions.
- The observed magnetic field dependence provides insights into vortex dynamics and pinning in SFS Josephson junctions.
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