High-Permeability Particles for Magnetic Composites Robert A. Sailer 1 , Pamela J. Jeppson 1 , Anthony N. Caruso 1 , Eric L. Jarabek 1 , Joseph A. Sandstrom 1 , Zoha Al-Badri 1 , Dean G. Grier 1 , Philip R. Boujouk 2 , Peter G. Eames 3 , Mark C. Tondra 3 and Douglas L. Schulz 1 * 1 Center for Nanoscale Science and Engineering, North Dakota State University, Fargo, ND 58102, USA 2 Research, Creative Activities & Technology Transfer, North Dakota State University, Fargo, ND 58102, USA 3 NVE Corporation, Eden Prairie, MN 55344, USA ABSTRACT Electromagnetic shields and flux concentrators for magnetic sensors could utilize flexible and insulating composites applied using simple thin film deposition methods such as dip- coating, spin-coating, spraying, etc. As the first step towards development of composites with superior performance, efforts focused on isolating nanoparticles with large magnetizations under low fields. In this paper, we provide the results of proof-of-concept studies for two systems: metal-functionalized silicone-based materials (metal-silicone); and, Co-ferrite (Co 2+ 1-x Fe 2+ x Fe 3+ 2 O 4 ) nanoparticles. The metal-silicone materials studied included a polysiloxane that contained a pendant ferrocene where an optimum saturization magnetization of 5.9 emu/g (coercivity = 11 Oe) was observed. Co-ferrite nanoparticle samples prepared in this study showed unprecendented saturation magnetization (i.e., M s > 150 emu/g) with low coercivity (H c ~ 10 Oe) at room temperature and offer potential application as flux concentrators. INTRODUCTION Ultra-high sensitivity magnetic sensors are typically comprised of a magnetic tunnel junction (MTJ) with ancillary components such as flux concentrators and magnetic shielding. In this example, flux concentrators focus the magnetic field on the MTJ while shielding improves device performance given enhanced signal-to-noise and reduced 1/f noise. Each of these components should be comprised of a material that exhibits a large change in magnetization at a small change in magnetic field. Such high permeability at zero field is observed in materials such as permalloy, co-netic, and other alloys. These multicomponent alloys are typically applied to device structures in foil form or are deposited using vacuum deposition (e.g., sputtering, evaporation) or by solution methods such as electrodeposition. In manufacturing settings, applications using foils may be limited by the lack of intimate contact which limits the ability to perform photolithographic definition (required for appropriate sensor function). Also, owing to the large coefficient of thermal expansion of metals, the thickness of thin films grown directly on substrate (e.g., by vacuum deposition or solution growth) limits the thickness of these layers and, ultimately, the level of flux concentration and shielding. To address these apparent limitations, the use of composites that utilize high permeability particles is presently under investigation. Nanoparticles are targeted for these applications as smaller domain sizes are known to give reduced coercivities. In addition, we have Mater. Res. Soc. Symp. Proc. Vol. 906E © 2006 Materials Research Society 0906-HH01-06.1