Enhanced exchange anisotropy of Ni-Fe/Mn-Ni bilayers fabricated under the extremely clean sputtering process

In order to clarify the influence of the impurities in the sputtering atmos phere on the exchange anisotropy of ferromagnet/antiferromagnet bilayers, N i-Fe/Mn-Ni films were prepared under different purities of the sputtering a tmosphere by changing the base pressure from 10(-11) Torr [extremely clean (XC) process] to 10(-7) Torr [lower grade (LG) process]. The correlation be tween the exchange anisotropy and the microstructure of the films is discus sed. As a result, we found that: (1) The exchange anisotropy was enhanced i n the XC processed films comparing to the LG processed ones, especially whe n the thicknesses of both the ferromagnetic and antiferromagnetic layers we re very thin. (2) The critical thicknesses of the antiferromagnetic layers were 110 and 150 Angstrom for the XC and the LG processed films, respective ly. (3) In the XC processed films, the fcc-[111] direction of the Ni-Fe gra ins were highly oriented perpendicularly to the film plane and an enlargeme nt of antiferromagnetic grains was observed. We conclude that the enhanceme nt of exchange anisotropy is caused by the enlargement of antiferromagnetic grains in the XC processed films. (C) 1999 American Institute of Physics. [S0021-8979(99)74708-0].