Microwave, structural, and magnetic properties of Cu/Fe/CoFe/Cu

Abstract

The structure and the static and dynamic magnetic properties of pure Fe films with a surface overlayer of Co9Fe1 were studied. These structures are potential components of spin-valve or tunneling devices in which small magnetic damping, large moment, low anisotropy and high spin polarization may be advantageous. The films are polycrystalline and have Cu under and over layers. The Fe layers studied are from 3 to 20 nm thick and the CoFe layer was usually 1 nm. With a CoFe overlayer we found a range of Fe thicknesses from below 4 to near 6 nm in which low coercivity and narrow ferromagnetic resonance (FMR) linewidth resulted. Both below and above this range the properties degraded, apparently because the 2 nm Cu top layer was inadequate to protect the Fe against oxidation. Using extended x-ray absorption fine structure, we found only bcc Fe; atomic force microscopy shows a systematic decrease in roughness with increasing thickness of Fe, which may explain the magnetic hardness for the thinnest films. Fe (5 nm)/CoFe (1 nm), with a Gilbert α∼0.004, has FMR linewidths about 2/3 those of Permalloy films of comparable thickness. For some applications investigated, distinct advantages can be obtained using the high Q of the ferromagnetic system.