Exchange Bias - A Tool To Observe Unusual Magnetic Properties

Igor Roshchin (Department of Physics and Astronomy, Texas A&M University)

Exchange bias, typically described as a proximity effect between a ferromagnet and antiferromagnet, is crucial for magnetic memories and spintronic devices (HDD, MRAM). While the exchange bias mechanism, including the origin and role of uncompensated magnetization in the antiferromagnets still remains a puzzle, this effect can be used as a powerful tool for studying properties of magnetic materials.

In the studies of thin films of nominally antiferromagnets, we made two striking observations: First, a new, unusual magnetic order in nanostructured materials can be formed, yielding a net magnetization which plays the key role in the exchange bias in FeF2. Second, non-magnetic materials, such as copper can modify magnetic properties of the magnetic material in close proximity (antiferromagnetic FeMn).

These conclusions are results of the systematic studies of "intrinsic exchange bias". In this effect, the hysteresis loops are shifted as in the traditional exchange bias, but here, only one magnetic layer is present, instead of two. While the synopses of the intrinsic exchange bias in these two materials are very similar, the underlying mechanisms are different. I will discuss the results of structural, magnetic, and neutron scattering studies combined with theoretical considerations. I will also highlight how exchange bias measurements can be used to obtain structural information about NiMn-based magnetic shape memory alloys.

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