H Harm Wieldraaijer

Band Structure and Density of States Effects in Co-Based Magnetic Tunnel Junctions

Utilizing Co/Al(2)O(3)/Co magnetic tunnel junctions with Co electrodes of different crystalline phases, a clear relationship between electrode crystal structure and junction transport properties is presented. For junctions with one fcc(111) textured and one polycrystalline (polyphase and polydirectional) Co electrode, a strong asymmetry is observed in the magnetotransport properties, while when both electrodes are polycrystalline the magnetotransport is essentially symmetric. These observations are successfully explained within a model based on ballistic tunneling between the calculated band structures (density of states) of fcc-Co and hcp-Co.

Crystalline and Interfacial Structure of Ultrathin Co Layers Grown on Pd(111): A 59Co NMR Study

59Co nuclear magnetic resonance (NMR) was employed to study the growth of ultrathin Co/Fe and Co/Cu layers on a Pd(111) single crystal on an atomic scale. Co starts to grow in a dense-packed fcc(111) structure on Pd(111), but for thicker layers a mixture of fcc(111) and hcp(0001) evolves. The top Co interface is found to be almost perfect. On the other hand, the Pd/Co interface is far from ideal. Co intermixes with the Pd and forms a CoPd interface alloy, which has consequences for the interpretation of the strong perpendicular magnetic anisotropy (PMA) observed in Pd(111)/Co/Pd.

Influence of electrode structure on magneto transport in magnetic tunnel junctions

Summary form only given. Introduction The properties of magnetic tunnel junctions are heavily influenced by the electronic structure of the magnetic electrodes. Theoretically this has been well established for some time. Experimentally there have been few conclusive observations of this influence, which is mainly due to the need for tunneling electrodes with a well-known physical and electronic structure which can be modulated. In this study Co/Al/sub 2/O/sub 3//Co junctions have been prepared with differently textured Co layers, by dc/rf magnetron sputtering on either FeMn- or Ta-buffer layers. The local physical structure of the electrodes is investigated directly by /sup 59/Co Nuclear Magnetic Resonance (NMR) in combination with X-Ray Diffraction (XRD).

Exchange anisotropy as a probe of antiferromagnetism in expanded face-centered-tetragonal Mn"001… layers

Manganese (Mn) grows coherent and with an expanded metastable face-centered-tetragonal (e-fct) structure on ultrathin fct Co(001)∕Cu(001) template layers. From the temperature dependence of the observed unidirectional Mn∕Co interface exchange anisotropy, an antiferromagnetic state with a blocking temperature around 410K is found for a 21 monolayer thick e-fct Mn(001) film. The temperature dependent coercivity enhancement of the Co films, which is induced by the proximity of the antiferromagnetic Mn layer, suggests a Neel temperature above 410K for this Mn phase.

Epitaxial growth and magnetic anisotropy of electrodeposited Ni and Co thin films grown on n-type GaAs

Summary form only given. Ferromagnetic films on semiconductors can be used in the fabrication of magnetic sensors, memories, and novel devices based on spin-dependent transport phenomena. Electrochemical deposition offers some advantages with respect to UHV techniques for the growth of these structures, such as the low temperature processing, which can limit the interdiffusion between the film and substrate, thus creating well defined interfaces. We have studied the electrochemical growth and magnetic anisotropy of Ni and Co on [001]- and [011]-oriented n-GaAs.