STRUCTURAL COMPARISONS OF ION-BEAM AND DE MAGNETRON-SPUTTERED SPIN VALVES BY HIGH-RESOLUTION TRANSMISSION ELECTRON-MICROSCOPY

We have used high-resolution transmission electron microscopy to compa re the nanostructures of ion-beam and de magnetron sputter-deposited g iant magnetoresistive (GMR) spin valves and to correlate nanostructure with magnetic properties. Very low coercivities and strong exchange b ias (<8 Oe, 125 Oe) were achieved in ion-beam-deposited spin valves of the form SO)/Co(20)/Cu(>25)/Co(20)/NiFe(50)/FeMn(150)/Ta(30 Angstrom) ; these were compared with typical de magnetron deposited structures o f the same kind, both with and without a Ta seed layer, which exhibite d similar and poorer exchange biasing but superior GMR ratios (to 8%.) Cross-sectional and plane-view samples were prepared of all three str uctures and examined by high-resolution electron microscopy. Near-perf ect (111)-textured fcc metal and c-axis hcp Co columnar grains were re vealed in the ion beam deposited sample, while some (10 degrees) dispe rsion of this texture and random grain orientations were observed in t he Ta-seeded and unseeded de magnetron sputter-deposited samples, resp ectively. No amount of the alpha-FeMn (A12) phase was observed in any of the films. Exchange bias strengths and coercivity of the top Co/NiF e/FeMn layers thus correlate strongly with the degree of (111) texture . (C) 1996 American Institute of Physics.