Journal of Magnetism and Magnetic Materials 185 (1998) 283—292 Spin-dependent tunneling in discontinuous metal/insulator multilayers B. Dieny!,",*, S. Sankar!,#, M.R. McCartney$, D.J. Smith$,%, P. Bayle-Guillemaud", A.E. Berkowitz!,# ! Center for Magnetic Recording Research, University of California, San Diego, La Jolla CA 92093-0401, USA " CEA/De & partement de Recherche Fondamentale sur la Matie % re Condense & e, 38054 Grenoble, France # Department of Physics, University of California, San Diego, La Jolla, CA 92093-0401, USA $ Center for Solid State Science, Arizona State University, Tempe, AZ 85287-1704, USA % Department of Physics and Astronomy, Arizona State University, Tempe, AZ 85287-1504, USA Received 12 December 1997 Abstract We have studied the structural, magnetic and transport properties of (Co/SiO 2 ) discontinuous multilayers. These multilayers consist of layers of Co particles embedded in an insulating SiO 2 matrix. The current-in-plane (CIP) and current-perpendicular-to-the-plane (CPP) resistivities of the discontinuous multilayers can be tuned independently over orders of magnitude by varying the nominal thicknesses of the metallic and insulating layers. Negative magnetoresistance (MR) due to spin-dependent tunneling has been observed in both CIP and CPP geometries. At room temperature the two magnetoresistive responses are similar, differing only in magnitude. At lower temperatures, the two responses are remarkably different. The CIP-MR saturates readily following the magnetization curve whereas the CPP-MR exhibits hysteresis up to magnetic fields higher than 20 kOe. These differences suggest the nature of the magnetic domain structure in each metallic plane. These systems should permit a combination of ease in preparation with high magnetoresistance sensitivity at low fields. ( 1998 Elsevier Science B.V. All rights reserved. PACS: 75.70.Cn; 75.70.Pa; 73.40.Gk; 73.40.Rw Keywords: Spin-polarized tunneling; Spin electronics; Discontinuous multilayers; Metal/insulator multilayers; Coulomb blockade 1. Introduction Magnetoresistance (MR) resulting from spin- dependent tunneling was first experimentally de- * Corresponding author. monstrated by Gittleman et al. in granular metal/ insulator (cermet) films [1]. Below the metallic percolation threshold, these cermet films consist of randomly distributed nanosized ferromagnetic metallic particles dispersed in an insulating matrix. The conductivity in these films has been extensively studied and explained by a combination of tunneling 0304-8853/98/$19.00 ( 1998 Elsevier Science B.V. All rights reserved. PII S0304-8853(98)00028-6