Effects of Mn concentration and deposition temperature on the giant magnetoresistive properties of ion-beam-deposited PtMn spin valves

We studied the effects of Mn concentration (C/sub Mn/) in PtMn antiferromagnets (AFs) and the deposition temperature (T/sub s/) of PtMn in bottom PtMn spin valves. The exchange coupling field (H/sub ua/) and the critical thickness of PtMn were found to depend strongly on C/sub Mn/. Spin valves made with the optimum C/sub Mn/ (51%) show an H/sub ua/ value of around 410 Oe even with 125-/spl Aring/-thick PtMn, compared to the saturation value of about 500 Oe for the spin valves with much thicker PtMn. For the T/sub s/ dependence study, the NiFeCr-NiFe underlayer, PtMn AF layer, and part of the CoFe pinned layer were deposited at T/sub s/ up to 300/spl deg/C, and the rest of the layers were deposited after cooling the spin valve down to ambient temperature. The spin valves deposited at T/sub s/>250/spl deg/C and with >150-/spl Aring/-thick PtMn show H/sub ua/ of around 250 Oe, as deposited (without postannealing). The H/sub ua/ values increase upon postannealing for the spin valves deposited at all the T/sub s/ studied (25/spl deg/C-300/spl deg/C). However, the ferromagnetic coupling field (H/sub f/) also increases with repetitive postannealing, the rate of H/sub f/ increase being lower for the spin valves deposited at higher T/sub s/. The sheet resistance of PtMn spin valves was found to increase both after postannealing and with increasing T/sub s/, consistent with the higher resistivity observed for thin PtMn films deposited at higher T/sub s/. These results are attributed to the smaller grain size and the higher degree of chemical ordering for PtMn in the postannealed spin valves deposited initially at higher T/sub s/, as deduced from X-ray diffraction.