GIANT MAGNETORESISTANCE AT LOW FIELDS IN [(NIXFE1-X)(Y)AG-1-Y]/AG MULTILAYERS PREPARED BY MOLECULAR-BEAM EPITAXY

The structural and magnetic properties of [111]-oriented multilayers comprising ferromagnetic films of Permalloy-silver alternating with Ag spacer films are described. The multilayers are grown by molecular-beam epitaxy on Pt(111) seed films on sapphire (0001) substrates at temperatures in the range 25-175 degrees C. For a series of multilayers with similar bilayer periods (similar or equal to 50 A Angstrom) the magnetoresistance (MR) is found to be strongly dependent on both growth temperature and subsequent annealing temperature. The multilayers exhibit a negative magnetoresistance in the as-grown state which more than doubles when the growth temperature is increased from 25 to 100 degrees C; however, the highest MR (peak 5.6%; maximum slope 0.4% per Oe) is obtained by annealing (at 400 degrees C) multilayers grown at 100 degrees C. The primary effects of annealing are an improvement of structural order, partial segregation of Ag from the ferromagnetic films into adjacent Ag films, a slight decrease in laminar order, and a reduction in long-wavelength roughness of the multilayer interfaces. No evidence is found for discontinuities in the magnetic layers with the highest MR.