Unusual Field Dependence of the Anomalous Hall Effect in Ta/Tb-Fe-Co

Experimental studies of the anomalous Hall effect are performed for thin-film Ta/Tb-Fe-Co over a wide range of temperatures and magnetic fields up to 3 T. Far from the compensation temperature (T-M = 277 K), the field dependence has a conventional shape of a single hysteresis loop; just below the compensation point, the dependence is anomalous with the shape of a triple hysteresis. To understand this behavior, we experimentally reveal the magnetic phase diagram and theoretically analyze it in terms of spin-flop-like phase transitions. In this case, we observe the dominance of the Fe-Co sublattice, which is a subject of the strong interaction with the Ta layer. This Fe-Co anisotropy enhancement is expressed in the appearance of abnormal wing-shaped hysteresis loops near the compensation point and, in the unusual phase diagram, where the first-order phase transition line deviates towards low temperatures. This effect can be useful for the design of ultrafast ferrimagnetic devices with desired switching parameters.