Exchange anisotropy in Ni82Fe18O{100}/Ni80Fe20 bilayers

Ni0.82Fe0.18O{100} epitaxial films, ranging in thickness from 70 to 1200 Angstrom, were grown by solid-source metal-organic chemical vapor deposition. The exchange field for 45 Angstrom Ni80Fe20 on Ni0.82Fe0.18O films reached 250 Oe at 200 Angstrom Ni0.82Fe0.18O and then stayed almost constant with increasing thickness of Ni0.82Fe0.18O. Furthermore, the coercivity for those films is only 55 Oe. The high exchange field and the low coercivity are attributable to the high in-plane anisotropy of Ni0.82Fe0.18O{100} and the uncompensated spins in the interface of Ni0.82Fe0.18O/Ni80Fe20. The blocking temperature of these films is 180 degrees C, lower than that of NiO/Ni80Fe20 (similar to 220 degrees C). The reduction of the blocking temperature may result from local Fe-O-Fe or Fe-O-Ni bonding, which loses the superexchange interaction at a lower temperature than the blocking temperature of NiO. (C) 1998 American Institute of Physics.