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

Abstract

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

High magnetoresistance permalloy films deposited on a thin NiFeCr or NiCr underlayer

“…The in-plane particle size of 120 Å thick permalloy films estimated from their diffraction pattern ͑after approximately accounting for the nonuniform strain contribution to the peak width by subtracting off the nonuniform strain measured for the permalloy films without the NiFeCr underlayer͒ was found to increase monotonically with increasing thickness of the Ni 0.49 Fe 0.12 Cr 0.39 underlayer, reaching a plateau value of Ϸ220 Å at a thickness of Ϸ42 Å, as reported previously. 12 The ⌬R/R enhancement thus correlates well with the particle size in the permalloy film. 12 The resistivity of permalloy films should decrease with increasing particle size due to their decreasing electron scattering at the grain boundaries.…”

“…Results of B -H loop tracer measurements reveal that the presence of Ni 0.49 Fe 0.12 Cr 0.39 either as an underlayer in a bilayer or as a spacer layer in a trilayer structure 12 does not significantly change the magnetic properties of the permalloy film. No change in the magnetic moment of the permalloy films ͑Ϸ760 emu/cc͒ due to the presence of the underlayer was observed, since the ratio of the magnetic moment of the permalloy film deposited with the underlayer to that without the underlayer is 1.001Ϯ0.049 over the thickness range studied.…”

“…The in-plane diffraction patterns for these three films were reported previously. 12 The diffraction patterns for film ͑a͒ show a poorly ordered, but predominately bcc phase with a high stacking fault density, judging from its broad ͑111͒ and absence of ͑200͒ reflections, and for film ͑b͒ an unoriented fcc phase with a powder-like distribution of the intensity of the ͑111͒, ͑200͒, ͑220͒, and ͑311͒ reflections. In striking contrast, the diffraction pattern of film ͑c͒ shows only a single, sharp ͑220͒ peak, indicating a strong ͑111͒ texturing consistent with the specular data.…”

“…12 The sputtering system ͑base pressure 1ϫ10 Ϫ7 Torr͒ is equipped with a substrate holder-mask arrangement that allows depositions under different conditions on each of, e.g., eight 1 in. wafers without breaking vacuum.…”

“…It reaches a maximum value at a critical thickness of Ϸ45 Å similar to that observed for the films deposited by rf diode sputtering. 12 The ⌬R/R values of these films can be further increased by postannealing in a vacuum furnace. In general, a ⌬R/R increase of Ϸ10% was observed after annealing at up to 400°C.…”