Influence of stress and unidirectional field annealing on structural and magnetic performance of PtMn bottom spin-filter spin valves

Abstract The influence of unidirectional field annealing (UDA) and subsequent stress annealing (SA) on the structure and magnetic response of PtMn bottom spin-filter spin-valve sensors with a NiFeCr/NiFe seed layer was investigated. A time constant of 1.17 h for the FCC–FCT phase transition of the PtMn layer was obtained upon UDA at 265°C in an external magnet field of 13 kOe, which is consistent with 1.1 h observed for the GMR. A lower time constant of 0.7 h was determined for the exchange interaction field. The SA with similar conditions as in the manufacturing environment leads to a UDA time-dependent alteration of sensor performance. A SA up to 38 h causes a GMR value reduction, which becomes more pronounced with increasing UDA duration prior to SA. Furthermore, SA causes a progressive oxidation of the Ta cap layer; in contrast, the exchange field remains nearly unaffected, particularly for the sensors with 5 or 6 h UDA. From the point view of application, an UDA treatment of (5–6) h yields the optimal sensor performance for the finished read-write head.