This kink is very similar to the phenomenon known as wasp-waist hysteresis. In this case, this phenomenon is explained by two reasons. The first is due to the mixture of grain sizes in the sample. If your sample contains hematite, the second reason could be for a difference between the coercivity of the hard magnetic phase (hexaferrite) and the soft magnetic phase (hematite).
I recommend you this article (https://doi.org/10.1029/95JB00672) in which I have found information about this phenomenon that may help you.