Exchange bias

Reversal of the ferromagnet's moment will have an added energetic cost corresponding to the energy necessary to create a Néel domain wall within the antiferromagnetic film.

This inequality means that the direction of the exchange bias can be set by cooling through TN in the presence of an applied magnetic field.

Generally, the process of field cooling from higher temperature is used to obtain ferromagnetic unidirectional anisotropy in different exchange bias systems.

Exchange anisotropy has long been poorly understood due to the difficulty of studying the dynamics of domain walls in thin antiferromagnetic films.

The amount of hysteresis shift Hb is not correlated with the density n of uncompensated spins in the plane of the antiferromagnet that appears at the interface.

In addition, the exchange bias effect tends to be smaller in epitaxial bilayers than in polycrystalline ones, suggesting an important role for defects.

Exchange bias was initially used to stabilize the magnetization of soft ferromagnetic layers in readback heads based on the anisotropic magnetoresistance (AMR) effect.

Currently, exchange bias is used to pin the harder reference layer in spin valve readback heads and MRAM memory circuits that utilize the giant magnetoresistance or magnetic tunneling effect.

Similarly, the most advanced disk media are antiferromagnetically coupled, making use of interfacial exchange to effectively increase the stability of small magnetic particles whose behavior would otherwise be superparamagnetic.

Desirable properties for an exchange bias material include a high Néel temperature, a large magnetocrystalline anisotropy and good chemical and structural compatibility with NiFe and Co, the most important ferromagnetic films.