ROLE OF THE BUFFER LAYERS IN DETERMINING THE ANTIFERROMAGNETIC COUPLING AND MAGNETORESISTANCE OF NIFECO CU SUPERLATTICES/

The antiferromagnetic (AF) coupling and magnetoresistance in magnetron -sputtered polycrystalline NiFeCo/Cu superlattices grown on Fe, Cr, or Zr buffer layers have been studied. The results show that the buffer layers significantly affect AF coupling and magnetoresistance through modulating the growth of specifically oriented crystalline multilayere d structures. Two types of buffer layer effects on AF coupling and mag netoresistance are considered: modifying interfacial roughness and pro ducing layer-thickness fluctuations. Interfacial roughness is formulat ed in the first Born approximation using data obtained from specular a nd off-specular (diffuse) x-ray scattering measurements. For the rough ness at interfaces, correlated interfacial roughness is found to predo minate and estimated to be as large as 5-7 Angstrom with a moderately large lateral correlation length scale xi that ranges from 120 to 200 Angstrom. Upon approximately the same AF coupling, for Fe or Cr buffer layered superlattices characteristic of well-defined, comparatively f lat layer structures throughout the entire specimen, magnetoresistance turns out to increase as the correlated interfacial roughness increas es. For the superlattices grown on Zr buffer layers in which the prese nce of columnar structures is confirmed, a constant, weak AF coupling and moderate magnetoresistance concur and are both almost independent of buffer layer thickness. These features are explained in terms of th e averaging of AF coupling and magnetoresistance through parallel laye r-thickness fluctuation structures approximating the columnar structur es. (C) 1997 American Institute of Physics.