Microstructure and interface evolution of PtMn bottom spin-filter spin valves induced by stress and unidirectional field annealing

Abstract

The microstructure evolution in PtMn-based bottom spin-filter spin valves was investigated to clarify the alteration of the sensor performance caused by different annealing treatments during manufacturing. Neither unidirectional field annealing (UDA) nor stress annealing (SA) for 38 h, which simulates the final quality test of the finished read-write head, have any significant influence on the texture of the sensor stack. UDA causes the appearance of domain boundaries in the PtMn layer as a consequence of the fcc–fct transformation together with some disturbance in the functional layers of the sensor, neither of which affect the giant magneto-resistive performance. The SA treatment causes an inter-diffusion in the NiFeCr/NiFe seed layers, some grain growth in PtMn, more serious disturbance of the functional layers, and complete amorphization of the Ta cap layer. In comparison to other studies of spin valves, the intermixing of seed layers in the present study does not appear to influence the PtMn/CoFe interface. The alteration of the sensor performance seems to be mainly caused by the inter-diffusion of the functional layers.