Exchange Bias and Its Phase Reversal in Zero Magnetization Admixed Rare-Earth Intermetallics

The exchange bias effect—an important attribute in many device applications— is traditionally discussed as a form of exchange anisotropy at the interface between the ferromagnetic/antiferromagnetic layers of two distinct systems. We report here on magnetically ordered alloys possessing the feature of unidirectional anisotropy that reverses its sign at a characteristic temperature. These alloys are admixed rare-earth (RE) intermetallics, comprising two dissimilar rare-earth ions, belonging to the two different halves of the $4f$ series. All $4f$ rare-earth ions exhibit ferromagnetic coupling between the spins of their ions and the conduction electrons. Magnetic moments of dissimilar RE ions in such admixed alloys, however, get antiferromagnetically coupled, and they display a magnetic compensation feature in which the field-induced reversal in the orientation of the magnetic moments of dissimilar rare-earth ions occurs at the compensation temperature $(T_{rm comp})$ . Above a threshold field, the conduction electron polarization also reverses its sign at $T_{rm comp}$. We suggest that this effect correlates with the observed phase reversal in the exchange bias field.