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 compos itions. It shows that loss of magnetoresistance with time at elevated tempe rature is less pronounced for synthetic structures, for thinner PtMn AFM fi lms exchange-annealed for relatively longer times, and Pt-rich compositions of PtMn, The lifetime temperature T-max is defined as the maximum operatin g temperature for the spin valve that results in less than a 10% drop in ou tput 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 H(e)x values. For H(e)x values and reverse field magnitudes for the sheet f ilm spin valve samples tested here, the tolerable UBR was in the 6-8% range , and Tmax values in the 170 degrees -205 degreesC range. Choosing the corr ect reverse field for DeltaT(b) measurements was important for synthetic st ructures because of the interaction between the applied field and the coupl ing field between the inner and outer pinned layers in the synthetic struct ure. Finished heads show T-max values that are lower by 40 degrees -55 degr ees for the five-year 50% duty cycle criterion compared to sheet films. Thi s highlights the importance of processing environments, especially in slide r fabrication, and imposes a further restriction on the acceptable sheet fi lm tolerable UBR, reducing it to 3-4%, Activation energies from lifetime te sts are in the range 2.2 to 2.6 eV for all samples including finished slide rs, which indicates that differences in lifetimes are not associated with l arge variability in the activation energy of depinning within the PtMn syst em. The time-dependence of magnetic properties such as interlayer coupling (H-ilc) and coercivity (H-c) of the free layer is very important and exhibi ts runaway behavior with time. It must be monitored for deleterious effects .