Exchange bias training effect in coupled all ferromagnetic bilayer structures.

Area of Science:

• Condensed Matter Physics
• Materials Science
• Magnetism

Background:

• Exchange coupled bilayers of soft and hard ferromagnetic thin films offer analogies to conventional antiferromagnetic/ferromagnetic exchange bias heterostructures.
• These ferromagnetic bilayers demonstrate a tunable exchange bias effect and distinct training behavior upon repeated hysteresis loop cycling of the soft layer.

Purpose of the Study:

• To investigate the training induced changes in the bias-setting hard magnetic layer of all-ferromagnetic bilayers.
• To determine the driving mechanism behind the exchange bias training effect in these systems.
• To compare experimental observations with theoretical predictions.

Main Methods:

• Fabrication of exchange coupled bilayers of soft and hard ferromagnetic thin films.
• Magnetometry measurements to observe hysteresis loops and training effects.
• Comparison of experimental data with a theory based on triggered relaxation phenomena.

Main Results:

• All-ferromagnetic bilayers exhibit tunable exchange bias and training behavior analogous to conventional systems.
• Training induced changes in the hard magnetic layer are observable via simple magnetometry.
• Experimental data strongly supports that the exchange bias training effect is driven by deviations from equilibrium in the pinning layer.

Conclusions:

• Exchange coupled ferromagnetic bilayers provide a model system for studying exchange bias and training effects.
• The study confirms that non-equilibrium conditions in the pinning layer are the primary drivers of the training effect.
• Excellent agreement between experimental results and triggered relaxation theory validates the proposed mechanism.