Domain wall pinning in Ni-gamma/alpha Fe-Ni multilayers

Zero field cooled measurements of DC magnetization, M-ZFC, at low field (7 Oe) for some (111) textured Ni-Fe-Ni multilayers with different Fe thicknes s, obtained by thermal evaporation have been carried out. The M-ZFC curves were measured in the temperature range 4.2-280 K. Here, we report results f or three samples with Fe layer thicknesses of 4, 8 and 16 Angstrom. The mul tilayers were grown on pseudohexagonal (0001)mica substrates and they were characterized by Mossbauer spectroscopy and scanning tunneling microscopy. The M-ZFC curves show a new behavior characterized by linear increases, as the temperature increases, with exceptionally high slope which depends on t he Fe layer thickness. This new behavior is discussed in terms of thermally activated depinning of domain wall, pinned by crystallographic defects and compositional variations. Both high-spin and low-spin states have been ide ntified. The FCC-BCC transition of gamma Fe has been identified between 8 a nd 16 Angstrom. (C) 2001 Published by Elsevier Science B.V.