Magnetoresistance study and interlayer coupling of CoFe/Os/CoFe thin films

The CoFe/Os/CoFe thin films were deposited on natural oxidized Si(1 0 0) substrates at room temperature by an ultra-high vacuum DC-magnetron sputtering system with a base pressure less than 1 x 10(-8) Torr. The thickness of the ferromagnetic layers was 100 angstrom in all cases and a series of trilayers with Os spacer ranging from 3 to 20 angstrom was made. Effects of the Os layer thickness on the magnetoresistance (MR) and magnetic properties were investigated. The results showed that the magnetism switched from ferromagnetic (Os thickness 3, 5 angstrom) to antiferromagnetic (Os thickness 7-13 angstrom) and then ferromagnetic (Os thickness 20 angstrom) again. From the MR study, we see that the AMR ratio decreased from 4.64% to the minimum value 0.69% at 9 angstrom and then increased; GMR ratio increased from 0.01% to the maximum value 0.43% at 9 angstrom and then decreased. From the hysteresis loops, the results exhibited that coercivity increased from 16 Oe to the maximum value 92 Oe at 9 angstrom and then decreased, and squareness value decreased from 0.97 to the minimum value 0.17 at 9 angstrom and then increased. Dependence of saturation field on Os spacer-layer thickness for CoFe trilayers showed a maximum value 216 Oe at 9 angstrom. This suggests that the small GMR effect may be related to the small exchange coupling strength in CoFe/Os/CoFe thin films. (C) 2006 Elsevier B. V. All rights reserved.