Reliability of PtMn-based spin valves

This paper addresses the lifetime characteristics of standard and synthetic spin valves of different PtMn antiferromagnet (AFM) thicknesses and compositions. It shows that loss of magnetoresistance with time at elevated temperature is less pronounced for synthetic structures, for thinner PtMn AFM films exchange-annealed for relatively longer times, and Pt-rich compositions of PtMn. The lifetime temperature T_max is defined as the maximum operating temperature for the spin valve that results in less than a 10% drop in output for a five-year 50% duty cycle. The generalized prediction of lifetime temperature T_max from the more usable unblocked ratio (UBR) point on the UBR-versus-temperature curve is complicated by test conditions and initial Hex values. For Hex values and reverse field magnitudes for the sheet film spin valve samples tested here, the tolerable UBR was in the 6-8% range, and T_max values in the 170°-205°C range. Choosing the correct reverse field for ΔT_b measurements was important for synthetic structures because of the interaction between the applied field and the coupling field between the inner and outer pinned layers in the synthetic structure. Finished heads show T_max values that are lower by 40°-55° for the five-year 50% duty cycle criterion compared to sheet films. This highlights the importance of processing environments, especially in slider fabrication, and imposes a further restriction on the acceptable sheet film tolerable UBR, reducing it to 3-4%. Activation energies from lifetime tests are in the range 2.2 to 2.6 eV for all samples including finished sliders, which indicates that differences in lifetimes are not associated with large variability in the activation energy of depinning within the PtMn system. The time-dependence of magnetic properties such as interlayer coupling (H_ilc) and coercivity (H_c) of the free layer is very important and exhibits runaway behavior with time. It must be monitored for deleterious effects