A series of Co/Mn/Co sandwiches was prepared on GaAs(001) surfaces at
room temperature via a molecular beam epitaxy (MBE) technique. Reflect
ion high-energy electron diffraction (RHEED) and x-ray-diffraction (XR
D) analysis indicated a polycrystalline structure. By standard magneto
resistance measurements, it was found that with a Mn spacer thickness
of 8 Angstrom, a seldom-seen positive magnetoresistance (PMR) as high
as 16% was exhibited at room temperature. The measurement under differ
ent geometries of H and I indicated that it was not an anisotropic mag
netoresistance (AMR) effect. The MR-H curve displayed no hysteresis in
contrast to the magnetometry measurement: An interface effect is prop
osed as a possible origin of this phenomenon. (C) 1997 American Instit
ute of Physics.