Spin polarization and barrier oxidation effects at the Co/alumina interface in magnetic tunnel junctions

Copyright © 2004 American Institute of PhysicsThe electronic structure and polarization in magnetic tunnel junctions prepared with varying degrees of barrier-layer oxidation have been studied using x-ray absorption spectroscopy across the Co L2,3 absorption edges. It was found that the Co electronic structure near the Co∕alumina interface tended to that of cobalt oxide as the barrier oxidation time was increased. However, the net Co 3d spin polarization, determined from x-ray magnetic circular dichroism, increased for moderate oxidation times compared to that obtained for an under-oxidized Co∕Al interface. It is proposed that the expected dilution of the measured polarization due to the formation of (room temperature) paramagnetic cobalt oxide, is offset by an increase in the Co 3d spin-polarization of the interface layer as the interface bonding changes from Co–Al to Co–O with increasing oxidation times

Mesoscovic magnetic/semiconductor heterostructures

We report the experimental results of Fe and Fe3O4 nanostructures on GaAs(100) surfaces and hybrid Ferromagnetic/Semiconductor/Ferromagnetic (FM/SC/FM) spintronic devices. Element specific x-ray magnetic circular dichroism (XMCD) measurements have shown directly that Fe atoms on the GaAs(100)-4 x 6 surface are ferromagnetic. Within coverages of 2.5 to 4.8 ML superparamagnetic nanoclusters are formed and exhibiting strong uniaxial anisotropy, of the order of 6.0 x 10(5) erg/cm(3). The coercivities of epitaxial Fe dot arrays films grown on GaAs(100) were observed to be dependent on the separation and size of the dots indicating that interdot dipolar coupling affects the magnetization processes in these dots. In addition Fe3O4 films grown on deformed GaAs(100) substrates have been observed to form nanostripes following the topography of the substrate and magneto-optical Kerr effect (MOKE) measurements showed that these nanostripes have uniaxial magnetic anisotropy with easy axis perpendicular to the length of the nanostripes. Meanwhile the FM/SC/FM vertical device has exhibited a biasing current dependent on MR characteristics, with a maximum change of 12% in the MR observed, indicating for the first time a large room temperature spin injection and detection

Experimental Observation of Dual Magnetic States in Topological Insulators

The recently discovered topological phase offers new possibilities for spintronics and condensed matter. Even insulating material exhibits conductivity at the edges of certain systems, giving rise to an anomalous quantum Hall effect and other coherent spin transport phenomena, in which heat dissipation is minimized, with potential uses for next-generation energy-efficient electronics. While the metallic surface states of topological insulators (TIs) have been extensively studied, direct comparison of the surface and bulk magnetic properties of TIs has been little explored. We report unambiguous evidence for distinctly enhanced surface magnetism in a prototype magnetic TI, Cr-doped Bi 2 Se 3 . Using synchrotron-based x-ray techniques, we demonstrate a “three-step transition” model, with a temperature window of ~15 K, where the TI surface is magnetically ordered while the bulk is not. Understanding the dual magnetization process has strong implications for defining a physical model of magnetic TIs and lays the foundation for applications to information technology

Magnetic structure near the Co/NiO(001) interface

We investigate the magnetic coupling at the Co/NiO interface using soft x-ray magnetic linear dichroism (XMLD) and circular dichroism taking explicitly into account the recently observed angular dependence of the XMLD with respect to the crystallographic axes. We find that the Co moments are aligned perpendicular to the NiO moments. We discuss the impact of the anisotropic XMLD on the intensity ratio of the two peaks at the Ni L{sub 2} edge, which is commonly employed to determine the spin orientation in antiferromagnets using XMLD