A quick search of the web gives a lot of references to self-biased ferrites primarily for circulators.  The idea being that, similar to most other bias concepts in the RF world, to get certain desirable properties out of the ferrite, the RF changes in magnetic field must be applied to a non-zero magnetic field (the bias).  This is normally done by applying a static magnetic field to the ferrite using a permanent magnet.  The RF magnetic field then rides on top of that causing the desired effect; usually a uni-directional/non-reciprocal behavior not seen in typical passive circuits.

The idea behind a so-called self-biasing ferrite is that the lattice structure is anisotropic and thus already has an ingrained bias in the material itself.  Techniques for doing this sort of thing are usually proprietary, but I could envision sintering the ferrite in the presence of a strong magnetic field to embed a certain bias similar to domain alignment of a permanent magnet.  And of course the term "self-biasing" may be a bit generous.  More likely it's a "low bias" such that the strength of the RF magnetic field is enough to get the desired behavior without externally applied field.  Conceptually this would be similar to a low bias diode detector.

That's interesting explanation , I would thank you very much.

I am working on ferrite substrate antenna trying to study their behavior by externally applied field and reduce the required bias to get same amount of tuning, even the behavior is complex but good features can be obtained on the cost of losses , the thing that motivated this question that researchers trying to avoid using bulk ferrite substrate by using "self-biased" films to get some features .

Thanks again

Self-bias ferrite is basically, concentrate signal density or change the polarisation. The permanent magnet is main source to have the effect.

For antenna, probably it can improve directivity or polarisation can be changed