Let us consider a magnetic system containing AFM and FM interface, that is able to exhibit exchange bias, and we need to check for exchange bias recording M-H loops as discussed in many literature. If the AFM phase were dominant, there is problem to saturate the M-H loops (Our system has Hmax = (+/-)1.5 T) and one could record just a minor loop. Consequently, the M-H loops will be shifted in field direction, showing as if there were exchange bias.
Let us assume that the loops are minor (that is what I have observed in my samples), which are shifted along -ve field axis. I have recorded the M-H loops for field-cooled samples (H = (+/-)2 kOe) for both +ve and -ve field, and observe a shift in the -ve side for +ve field cooling and vice-versa. My question is:
If the shifting is due to MINOR LOOP effect, can the direction of loop shifting depend on the polarity of cooling field as that I have obtained? What I believe is that if the loops were MINOR the shifting should have been in the same direction ( I may be wrong).
If by cooling you go through the Néel temperature of the antiferromagnet (i.e. you start in its paramagnetic regime) then the sign of the EB shift is always opposite to the sign of the cooling field. That is irrespective of the fact whether later you can perform a major loop.
The reason is that the interaction fixing the bias is not so mauch the field applied while cooling (this "only" tells the ferromagnet what to do) but the exchange interactions at the FM/AFM interface.
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