Determining Magnetic Structures of Metallic Multilayers Using Polarized Neutron Reflectivity Analysis. J.A. Borchers^*, J.A. Dura^*, P.M. Gehring^*, R.W. Erwin^*, C.F. Majkrzak^*, J.F. Ankner⁺, S.Y. Hsu^SS, J. Bass^SS, W.P. Pratt, Jr.^SS, J.K. Howard^[daggerdbl], M.A. Parker^[daggerdbl], T.L. Hylton^[daggerdbl], and K.R. Coffey^[daggerdbl], ^*Reactor Division, NIST, Gaithersburg, Maryland, ⁺Missouri University Research Reactor, Columbia, Missouri, ^SSMichigan St. University, East Lansing, Michigan, ^[daggerdbl]IBM Storage Systems Division, San Jose, California

Within the past decade, giant magnetoresistance (GMR) has been observed in a variety of transition-metal multilayer systems. Specular (Q_z) neutron reflectivity measurements have confirmed that the largest GMR is associated with an antiferromagnetic coupling of ferromagnetic layers across non-magnetic interlayers. In general, specular polarized neutron reflectivity provides a depth profile of the magnitude and direction of the magnetic moment if the in-plane domains are sufficiently large (>100 um). Conversely, off-specular (Q_x) diffraction is sensitive to smaller domains. We have measured the specular and off-specular reflectivity of Co(6 nm)/Cu(6 nm) and annealed Ni_.8Fe_.2(2 nm)/Ag(4 nm) multilayers, both of which exhibit a 4-5% GMR effect. We do not observe any magnetic scattering in polarized specular reflectivity scans taken in remanence. Instead, magnetic diffuse scattering appears in off-specular scans. For the annealed Ni_.8Fe_.2/Ag multilayers, this diffuse scattering is weak and broad in both the Q_z and Q_x scan directions. Thus, some portion of the Ni_.8Fe_.2 moments order in small (1 to 10 um) in-plane domains that are primarily uncorrelated along the growth axis. For as-prepared Co/Cu samples, this diffuse scattering is strongly peaked in Q_z. In this case, the small in-plane domains are antiferromagnetically correlated along the growth axis. Our neutron data show that the interlayer interaction is altered by field cycling, and the GMR is consequently reduced. We will discuss the status of our efforts to extract quantitative information from these off-specular data.